The ShakeAlert Earthquake Early Warning System and the Federal Role

The ShakeAlert Earthquake Early Warning System and the Federal Role

The ShakeAlert Earthquake Early Warning
June 1, 2022
System and the Federal Role
Linda R. Rowan
Portions of all 50 states, as well as U.S. territories and the District of Columbia, are
Analyst in Natural
vulnerable to earthquake hazards and associated risks to varying degrees. Among the
Resources Policy
costliest U.S. earthquake disasters was the 1994 magnitude 6.7 Northridge earthquake in

California, which caused 60 fatalities and more than 7,000 injuries; left about 20,000
homeless; damaged more than 40,000 buildings; and caused an estimated $13-$20

billion in economic losses. Earthquake early warning (EEW) is one way to reduce earthquake risks (i.e., fatalities
and injuries, as well as damage to structures and operations). EEW refers to sending a warning to areas that may
experience the highest intensity shaking; the EEW is sent after an earthquake is detected, but before damaging
ground-shaking reaches the areas. An EEW received in tens of seconds to minutes before shaking allows
institutions and individuals to take protective actions (e.g., an institution can automatically stop a train to prevent
derailment or an individual can avoid getting into an elevator to avoid harm).
EEW is among the most challenging of emergency communications. Earthquakes cannot be predicted and occur
suddenly, and mass notification to high-risk areas must occur within seconds of earthquake detection to be
effective. Congress directed the U.S. Geological Survey (USGS) to establish EEW capabilities in 2018 (42 U.S.C.
§7704(a)(2)(D)), as part of the reauthorization of the National Earthquake Hazards Reduction Program (NEHRP).
Under the Stafford Act (42 U.S.C. §5132), the USGS has authority through the President to provide alerts about
earthquakes using federal and other communication services to states and civilian populations in endangered
areas.
Development of Earthquake Early Warning in the United States
An EEW system consists of the following components:
 An understanding of earthquakes and faults to know where to locate an earthquake-sensing
network
 An earthquake-sensing network that can detect the start of an earthquake in real time
 Robust and rapid telemetry (i.e., continuous transmission of instrument readings to data centers)
 Data analysis and alert decisionmaking
 A targeted and clear alert message
 Rapid mass notification through communication services to areas at risk
The USGS, with various federal, state, academic, and private partners, began public EEW on the West Coast via
the ShakeAlert Earthquake Early Warning System (ShakeAlert) in California in 2019 and in Oregon and
Washington in 2021. ShakeAlert started as a prototype EEW system in 2012. From FY2006 through FY2021, the
USGS spent an estimated $132 million for EEW activities, including ShakeAlert; other nonfederal partners
contributed $84 million for ShakeAlert between 2012 and 2021. In 2018, the USGS estimated annual operation
and maintenance costs for ShakeAlert starting at about $40 million. The USGS aims to expand ShakeAlert into
Alaska, Hawaii, and Nevada. In FY2022, Congress appropriated $28.6 million to the USGS for ShakeAlert and
$1 million for ShakeAlert implementation planning in Alaska.
ShakeAlert sent 51 public alerts for earthquakes that caused light shaking and little damage between October
2019 and December 2021. EEWs sent via the Federal Emergency Management Agency (FEMA) communication
pathways often did not arrive before intense shaking; these warnings frequently were delayed more than five
seconds or were not delivered due to technical glitches. EEWs sent via cell phone applications over Wi-Fi or
cellular networks were fast (i.e., with delivery delays of less than five seconds), giving cell phone owners enough
time in most cases to take protective actions before ground shaking arrived.
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The ShakeAlert Earthquake Early Warning System and the Federal Role

Oversight and Policy Considerations
Congress may consider providing direction on policy priorities related to the authorities and mandates of the
NEHRP Reauthorization Act of 2018 (P.L. 115-307) and the Stafford Act to expand, contract, or change EEW
capabilities in the United States. Congress may seek additional information to assess ShakeAlert’s performance
and effectiveness. In addition, Congress may seek more information about the ability of FEMA communication
pathways to provide rapid and targeted mass notification for earthquakes. Relatedly, Congress may explore policy
options for improving FEMA communication pathways.
If Congress chooses to continue providing funding for EEW generally and ShakeAlert specifically, it may
consider a range of options to do so, such as through annual appropriations or shared costs that are a mix of
federal- and state-funded initiatives. Other funding options for consideration may include funding aspects of
ShakeAlert through established or new National Science Foundation or FEMA federal grants, contracts, or
cooperative agreements. In addition, Congress may consider policy options that would enable the National
Oceanic and Atmospheric Administration or the National Aeronautics and Space Administration to contribute
funds for EEW capabilities. Congress also may consider providing appropriations for NEHRP and allowing the
program to establish priorities for ShakeAlert vis-à-vis other NEHRP priorities.

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Contents
Introduction ..................................................................................................................................... 1
Federal Role in Identifying Earthquake Risks ................................................................................. 3
Background and Authority to Issue Earthquake Early Warnings .................................................. 10
The ShakeAlert System ................................................................................................................. 12
Earthquake-Sensing Network .................................................................................................. 18
Data Processing, Analysis, and Alert Message Generation ..................................................... 22
Communication of Earthquake Early Warnings ...................................................................... 22
FEMA Communication Pathways ..................................................................................... 25
Other Communication Pathways ...................................................................................... 26
Performance: Speed and Accuracy of Earthquake Detection and Alert Messaging ................ 29
Communication Pathways Performance: Delivery of Earthquake Early Warnings ................ 29
Public Reaction to Earthquake Early Warnings ...................................................................... 30
ShakeAlert Administration ............................................................................................................ 31
Responsibility and Governance ............................................................................................... 31
Funding Trends and Estimated Future Costs for ShakeAlert .................................................. 33
USGS ShakeAlert Funding ............................................................................................... 33
Other ShakeAlert Funding ................................................................................................ 34
2018 Estimate of Costs to Complete ShakeAlert .............................................................. 35
Comparison of ShakeAlert with Other Earthquake Early Warning Systems ................................ 36
Issues for Congress ........................................................................................................................ 38

Figures
Figure 1. Plate Tectonics ................................................................................................................. 5
Figure 2. Major Faults on the West Coast of North America .......................................................... 7
Figure 3. USGS Seismic Hazard Map ............................................................................................. 8
Figure 4. FEMA Annualized Earthquake Losses........................................................................... 10
Figure 5. Schematic of the ShakeAlert System ............................................................................. 14
Figure 6. ShakeAlert System from Detection to Protection .......................................................... 15
Figure 7. Seismic Stations Contributing to ShakeAlert as of February 2022 ................................ 20
Figure 8. Geodetic Stations Contributing to ShakeAlert as of February 2022 .............................. 21
Figure 9. Alert Communication Pathways and Minimum Thresholds .......................................... 24
Figure 10. FEMA Communication Pathways ................................................................................ 26
Figure 11. Timeline of Public EEW by Country or Region and Population Size Alerted ............. 38

Figure A-1. Earthquake Magnitude and Energy Released............................................................. 42
Figure A-2. Earthquake Hazards ................................................................................................... 45

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Tables
Table 1. Examples of Protective Actions That May Be Taken After Receiving an
Earthquake Early Warning ......................................................................................................... 15
Table 2. ShakeAlert Nonfederal Partners ...................................................................................... 17
Table 3. Regional Networks That Contribute to ShakeAlert ......................................................... 19
Table 4. ShakeAlert License to Operate Partners, as of 2021 ....................................................... 27
Table 5. USGS Enacted Appropriations for EEW Activities and ShakeAlert ............................... 33
Table 6. Nonfederal Funding for the ShakeAlert System .............................................................. 35
Table 7. USGS 2018 Estimate of ShakeAlert Costs ...................................................................... 36

Table A-1. Modified Mercalli Intensity Scale ............................................................................... 43

Appendixes
Appendix. Earthquake Magnitude, Shaking Intensity Scale, and Hazards ................................... 41

Contacts
Author Information ........................................................................................................................ 45

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Introduction
An earthquake starts by the sudden movement of rocky material under the Earth’s surface along a
plane of weakness (i.e., a fault). Seismic waves radiate outward from the starting point of the
earthquake, much like radial waves moving outward from a drop of water.1 Intense ground
shaking from the seismic waves and motion from the fault slip that reaches the surface may
damage people and property and may cause commercial, government, educational, social,
cultural, and economic losses. An earthquake also may trigger other hazards, such as tsunamis or
landslides.2 Damaging earthquakes may impact local, regional, national, or international societies,
and many governments establish and direct programs to understand earthquake hazards and
reduce earthquake risks to protect their communities.3 Congress provides direction, oversight, and
funding for earthquake research to understand earthquake hazards, reduce earthquake risks,
understand geologic structure below the surface, detect underground nuclear explosions, and for
other purposes.
An important tool to monitor earthquake activity and mitigate the risk is an earthquake early
warning (EEW) system.4 An EEW requires detecting the start of an earthquake (i.e., near the
earthquake’s origin time) and warning high-risk areas that damaging ground shaking may arrive
within seconds to minutes of receiving the warning.5 An EEW system consists of a real-time
earthquake-sensing network, data communications, data analysis, alert formulation, and an alert
message distribution system. The earthquake-sensing network consists of an array of earthquake-
sensing stations that continuously and autonomously monitor for earthquakes near faults. A
station consists of seismic and/or geodetic instruments, power supplies, telemetry, and structures
to protect the instruments and electronics.6
Seismic instruments, which include seismometers and accelerometers (sometimes called strong
ground motion accelerometers or strong ground motion instruments), detect and measure the
properties of earthquakes, especially the arrival of the first seismic waves and the earliest
estimated location and magnitude (M) of the event.7 A seismometer near an earthquake may not
be capable of providing real-time data for large magnitude (M7.0+) earthquakes, causing a delay
in detection, because the instrument cannot record large ground motion that originates close to the
seismometer. As a result, some seismometers may not be used for EEW; other instruments, such

1 For more details, see the U.S. Geological Survery (USGS), “What Are the Effects of Earthquakes?,” at
https://www.usgs.gov/natural-hazards/earthquake-hazards/science/what-are-effects-earthquakes?qt-
science_center_objects=0#qt-science_center_objects.
2 See the Appendix for more information about earthquake hazards.
3 Richard M. Allen et al., “The Status of Earthquake Early Warning Around the World: An Introductory Overview,”
Seismological Research Letters, vol. 80, no. 5 (September/October 2009), at https://doi.org/ 10.1785/gssrl.80.5.682.
4 Jessica A. Strauss and Richard M. Allen, “Benefits and Costs of Earthquake Early Warning,” Seismological Research
Letters, vol. 87, no. 3 (May/June 2016), pp. 765-772, at https://doi.org/10.1785/0220150149 (hereinafter Strauss,
“Benefits,” 2016).
5 USGS, “Earthquake Early Warning – Overview,” at https://www.usgs.gov/programs/earthquake-hazards/science/
earthquake-early-warning-overview.
6 Telemetry is the automated recording and transmission of data from stations to processing centers.
7 For earthquake early warning (EEW), location and magnitude (amount of energy and size of the earthquake) are
estimated rapidly to determine if and where damaging ground shaking might occur. Ground shaking intensity is
described using the Modified Mercalli Intensity Scale (MMI), where MMI I is the lowest intensity and MMI X is the
highest intensity. See Appendix for more information about magnitude, shaking intensity, and hazards.
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as geodetic instruments, help provide data for EEW in these circumstances.8 Geodetic instruments
on the ground measure ground displacement and peak ground acceleration caused by an
earthquake using a Global Navigation Satellite Systems (GNSS) receiver.9 The geodetic data
recorded by geodetic instruments do not go off scale, regardless of the earthquake’s magnitude or
location. Geodetic data provide critical real-time information about ground motions to estimate
large magnitude (M7.0+) events for EEW, especially for those events where the seismic data may
be unavailable for the reasons described above.
Generally, an EEW should be communicated within 20 seconds of the earthquake’s origin time,
so institutions and individuals have enough time to take protective action before intense ground
shaking arrives at their locations. EEW does not work for individuals and institutions very close
to an earthquake because there is not enough time to detect the event and communicate a warning
before intense ground shaking reaches nearby locations.10
An understanding of earthquakes and their hazards is essential to establish an effective EEW
system.11 Observing and measuring the characteristics of earthquakes helps to determine why
they happen, where they occur, how frequently they may occur, and how much of a risk they may
pose to society. Some earthquakes produce earthquake hazards, such as ground shaking and
ground displacement; these hazards can cause damage and, in rare but significant cases, can cause
catastrophic damage. Earthquakes cannot be predicted, so to prepare and respond to the sudden
onset of a potentially catastrophic event, an EEW system needs to rapidly and accurately detect
the starting time and initial location of a damaging earthquake and estimate where the most
intense ground shaking may occur.
Congress established the National Earthquake Hazards Reduction Program (NEHRP) in 1977
(Earthquake Hazards Reduction Act; P.L. 95-124, 42 U.S.C. §7704) as a coordinated federal
program focused on understanding earthquake hazards and reducing earthquake risks, including
by warning the public about earthquakes. Four agencies—the U.S. Geological Survey (USGS),
National Science Foundation (NSF), Federal Emergency Management Agency (FEMA), and
National Institute of Standards and Technology (NIST)—constitute the program. Congress
appropriated $160 million for NEHRP in fiscal year (FY) 2021.12 NEHRP is mandated to reduce
earthquake risks via three strategies:

8 Geodesy is the science of accurately measuring and understanding the Earth’s geometric shape, orientation in space,
and gravity field, and geodetic is anything related to geodesy.
9 Geodetic instruments provide positions that are accurate to a few millimeters to centimeters in optimal conditions, and
this accuracy is important for earthquake measurements. The Global Navigation Satellite Systems (GNSS) receivers are
similar to “GPS receivers” found in mobile devices in the basic way that they work. The receivers gather satellite
signals from the GNSS, which includes the U.S.-operated Global Positioning System (GPS) constellation of satellites,
and determine their position in space and time. GPS receivers in mobile devices are miniaturized and not fixed (or
stably mounted in one position) and are therefore less accurate in defining their position than geodetic instruments in
earthquake-sensing networks.
10 Jeffrey J. McGuire et al., Expected Warning Times from the ShakeAlert® Earthquake Early Warning System for
Earthquakes in the Pacific Northwest, USGS, USGS Open File Report No 2021-1026, 2021 (hereinafter USGS,
Expected Warning Times, 2021).
11 Richard M. Allen and Diego Melgar, “Earthquake Early Warning: Advances, Scientific Challenges, and Societal
Needs,” Annual Review of Earth and Planetary Sciences, vol. 47 (2019), pp. 361-388, at https://doi.org/10.1146/
annurev-earth-053018-060457 (hereinafter Allen and Melgar, “EEW Advances,” 2019).
12 See CRS Report R43141, The National Earthquake Hazards Reduction Program (NEHRP): Issues in Brief, by Linda
R. Rowan, for more on NEHRP.
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1. Understanding the hazards and assessing the risks
2. Mitigating the hazards by facilitating hazard-resistant structures
3. Warning about the hazards so actions may be taken to reduce risks13
In 2018, Congress directed the USGS, with international, federal, state, and local partners, to
develop an EEW capability (P.L. 115-307, 42 U.S.C. §7704(a)(2)(D)). The first operational EEW
system in the United States, ShakeAlert on the West Coast, provides warnings to individuals and
institutions about intense ground shaking reaching their location in a matter of seconds to minutes
from an earthquake detection. ShakeAlert consists of an earthquake-sensing network of seismic
and geodetic stations that detect an earthquake and data processing centers with algorithms and
decisionmaking software that prepare alert messages. The alert messages contain the estimated
earthquake location, earthquake magnitude, and the areas that may receive intense ground
shaking in an estimated time period. ShakeAlert has been developed and tested and is now
operated, maintained, and improved based on past and current earthquake research and
earthquake-sensing technology development. ShakeAlert began operations in California in 2019
and expanded operations into Oregon and Washington in 2021.14 ShakeAlert had issued 51 public
alerts by the end of 2021.15 The USGS leads the ShakeAlert project and coordinates the work of
other federal and nonfederal partners. ShakeAlert is funded by federal and nonfederal partners.
The system does not eliminate all risks but is one component of NEHRP’s objective to reduce
earthquake risks. This report focuses on ShakeAlert and concludes with a discussion of potential
issues for Congress regarding funding, policy, and priorities for EEW in the United States.
Federal Role in Identifying Earthquake Risks
The USGS and FEMA assess earthquake hazards and identify earthquake risks in the United
States, as directed and funded by NEHRP. An effective EEW system to reduce risks may be
established where the earthquake risks are the highest. The USGS Earthquake Hazards Program
(EHP) conducts earthquake research; studies and catalogs earthquake activity; maps faults;
assesses earthquake hazards; and prepares earthquake notifications that include estimates of
earthquake hazards and damage, as well as information about an earthquake and its fault.16
FEMA’s Risk Management Program provides resources to identify and assess risks from natural
hazards and consider ways to minimize these risks.17

13 Hazard is not the same as risk; hazard is a source of danger, whereas risk is the possibility of loss or injury.
Earthquake hazards are related to an earthquake causing intense ground shaking and other damaging effects. The
degree of earthquake hazards is related to the probability of certain damaging effects caused by an earthquake
occurring within a certain period. The degree of earthquake risks is the combination of the degree of earthquake
hazards and the extent of the affected population (which includes the infrastructure supporting that population).
Therefore, in general, large population centers may be at higher risk than small population centers for the same degree
of earthquake hazards. See Appendix for more information about earthquake hazards.
14 ShakeAlert, “ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States,” at
https://www.shakealert.org/; USGS, “ShakeAlert,” at https://earthquake.usgs.gov/data/shakealert/; and Douglas D.
Given et al., Revised Implementation Plan for the ShakeAlert System: An Earthquake Early Warning System for the
West Coast of the United States, USGS, Open-File Report 2018–1155, 2018 (hereinafter USGS, ShakeAlert Plan,
2018).
15 ShakeAlert, “Post ShakeAlert Message Summaries,” at https://www.shakealert.org/education-outreach/event-review-
files/.
16 See USGS, “Earthquake Hazards Program,” at https://earthquake.usgs.gov/.
17 See Federal Emergency Management Agency (FEMA), “Risk Management,” at https://www.fema.gov/emergency-
managers/risk-management.
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The USGS National Earthquake Information Center maintains the Comprehensive Earthquake
Catalog (ComCat), an archive of earthquakes in the United States and significant earthquakes
globally.18 ComCat earthquake summaries, which provide information to assess the hazards and
risks from each event, are a public resource. These summaries are posted as soon as possible after
an event and may be updated over time to provide the most accurate information about the
earthquake and its impact. The ComCat data are used to test EEW systems using past earthquake
scenarios, and ComCat posts summaries of ShakeAlert performance for alerts for earthquakes in
California, Oregon, and Washington.19
The USGS Earthquake Notification System (ENS) provides earthquake information to individuals
and institutions that sign up to receive notifications.20 ENS points to the ComCat summary page
for an event as soon as information is available. Earthquake notification information is useful to
emergency responders and post-earthquake recovery, as it identifies regions that may be
damaged.
ComCat technical data are a resource for researchers trying to understand earthquakes and
earthquake hazards. Catalogs of past earthquakes identify active faults, how the faults are
changing with time, and where earthquakes may be likely to occur in the future. Past earthquake
assessment, current earthquake monitoring, and research helps the USGS identify and map active
faults and their associated earthquake hazards.
Many earthquakes occur at the boundaries between large sections (plates) of the Earth’s crust.
These areas are referred to as plate tectonic boundaries (Figure 1). Most of the largest magnitude
and most damaging earthquakes in the geologic record occur at collisional boundaries between
major tectonic plates. Two major types of collisional boundaries, subduction zones and strike-slip
zones, are of most concern to society because of the potential for damaging earthquakes.21 Many
subduction zones occur offshore, below the water surface. In some cases, when an earthquake
occurs on a submarine subduction zone, the earthquake may trigger a tsunami (Figure 1).

18 See USGS, “National Earthquake Information Center (NEIC),” at https://www.usgs.gov/programs/earthquake-
hazards/national-earthquake-information-center-neic.
19 ShakeAlert performance metrics for earthquake detections are posted with the event summary on ComCat for
earthquakes of magnitude 4.0 or larger. Performance metrics for all earthquake detections (i.e., magnitude greater than
3.5) that lead to the preparation and distribution of alert messages are posted on the ShakeAlert website: ShakeAlert,
“Post ShakeAlert Message Summaries,” at https://www.shakealert.org/education-outreach/event-review-files/.
20 See USGS, “Earthquake Notification System,” at https://earthquake.usgs.gov/ens/.
21 Subduction zones are where tectonic plates converge, such that one plate is forced to bend and dive underneath
another plate in a process called subduction by geoscientists (see USGS, “Introduction to Subduction Zones: Amazing
Events in Subduction Zones,” at https://www.usgs.gov/special-topics/subduction-zone-science/science/introduction-
subduction-zones-amazing-events. Strike-slip zones are where tectonic plates laterally slide past each other and create a
zone of faults where the two plates converge (see Britannica, “Strike-Slip Fault,” at https://www.britannica.com/
science/strike-slip-fault).
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Figure 1. Plate Tectonics

Source: USGS, “Plate Tectonics Mapping,” at https://pubs.usgs.gov/gip/99/pdf/gip99_ppt.pdf.
Notes: Divergent boundaries (red lines) denote rift zones or primarily normal fault type of motion (plates are
pul ing apart). Convergent boundaries (green saw tooth lines) denote subduction zones or primarily thrust fault
types of motion (plates are pushing together). Transform boundaries (blue lines) denote primarily laterally sliding
plate boundaries or primarily strike-slip fault type of motion (plates are sliding past each other). The lines
generalize and approximate the surface trace of more complicated geologic structures that consist of many fault
branches, and most plate boundaries reach the surface under water (i.e., submarine surface trace; shown by the
colored lines in the blue ocean water on this figure). Major plate col isions expressed on the surface of major
continents (shown by the lines on the tan continents on this figure) include the San Andreas Fault System
(primarily strike-slip faulting) in California, the Great African Rift System (primarily normal faulting) and the
continent-continent col ision of the Indo-Australian Plate with the Eurasian Plate (primarily thrust and strike-slip
faulting), creating the highest mountain range, the Himalayas.
The collisional boundaries that present the greatest earthquake hazards for the United States and
its territories are three different subduction zones, offshore of Alaska, the Pacific Northwest, and
Puerto Rico, and one strike-slip zone in California (Figure 1). The most active (i.e., have the
most frequent earthquakes) and damaging subduction zones (i.e., have the potential to have large
magnitude [M7.0+] events and may trigger tsunamis) that directly impact coastal populations and
infrastructure in the United States are
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 the Aleutian Arc Subduction Zone bordering southern Alaska,22
 the Cascadia Subduction Zone bordering the western coastlines of northern
California, Oregon, and Washington,23 and
 the Puerto Rico Trench Subduction Zone near Puerto Rico and the U.S. Virgin
Islands.24
The San Andreas Fault System (SAF), which stretches about 800 miles from the Gulf of
California through the state of California and then offshore just north of San Francisco (Figure
2), is a strike-slip fault system created by two tectonic plates that are sliding against each other.
The Pacific Plate is sliding against the North America Plate, producing a wide area of multiple
faults, including the San Andreas Fault. The collision of the plates produces many earthquakes,
primarily in the shallow crust and because these earthquakes are shallow, they may produce
intense ground shaking and/or ground displacement at the surface. Because the faults are
extensive, an earthquake may slip over a large area and may produce large magnitude earthquakes
(M7.0+). California is a high earthquake risk state because of the many shallow earthquakes on
active and extensive faults near populated areas or areas with critical infrastructure (e.g.,
pipelines, roads, bridges, dams, and aqueducts).

22 The Pacific Plate subducts beneath the North America Plate along the Aleutian Arc Subduction Zone offshore of
southern Alaska and the Aleutian Islands. The Aleutian Arc Subduction Zone has generated multiple M8.0+ earthquake
and tsunami sequences and these sequences may recur in the future. Six great earthquakes have occurred along the
Aleutian Arc Subduction Zone since 1900: 1906 M8.4 Rat Islands, 1938 M8.6 Shumagin Islands, 1946 M8.6 Unimak
Island, 1957 M8.6 Andreanof Islands, 1964 M9.2 Prince William Sound, and 1965 M8.7 Rat Islands, Harley M. Benz
et al., Seismicity of the Earth 1900-2010 Aleutian Arc and Vicinity, USGS, Open-File Report 2010-1083-B, at
https://pubs.er.usgs.gov/publication/ofr20101083B. The small population and sparse built environment limit the
damage from these events and account for the lower earthquake risk in Alaska compared with some other states. Large
Alaskan earthquakes may cause greater damage further away because of the tsunamis they trigger. Hawaii in particular
has suffered significant losses from tsunamis triggered by Alaskan earthquakes. The 1946 M8.6 Aleutian Islands
earthquake generated a tsunami, and the tsunami caused 5 fatalities in Alaska and 129 fatalities plus $26 million in
1946 dollars in damage in Hawaii.
23 The Juan de Fuca Plate subducts beneath the North America Plate along the Cascadia Subduction Zone (CSZ)
offshore of Northern California, the Pacific Northwest, and parts of British Columbia, Canada. M8.0+ earthquakes,
many with tsunamis occur on the CSZ every 570-590 years, on average. There is evidence of at least 12 M8.0+
earthquakes on the Cascadia Subduction Zone over the past 6,700 years. Robert C. Witter, Harvey M. Kelsey, and
Eileen Hemphill-Haley, “Great Cascadia Earthquakes and Tsunamis of the Past 6700 Years, Coquille River Estuary,
Southern Coastal Oregon,” Geological Society of America Bulletin, vol. 115, no. 10 (October 1, 2003), pp. 1289-1306.
The last large magnitude earthquake (between M8.7 and M9.2) that triggered a large tsunami was in January 1700,
more than 500 years ago, Brian F. Atwater, The Orphan Tsunami of 1700 (Reston, VA: University of Washington
Press/USGS, 2005). Earthquake probability forecasts estimate a 14% chance of a M8.0+ earthquake on the CSZ over
the next 50 years, Alan Boyle, “Earthquake Experts Lay Out Latest Outlook for the ‘Really Big One’ That’ll Hit
Seattle,” GeekWire, February 15, 2020.
24 For more details about earthquake hazards and risks to Puerto Rico and the U.S. Virgin Islands, see National Oceanic
and Atmospheric Administration (NOAA) Ocean Explorer, “The Puerto Rico Trench: Implications for Plate Tectonics
and Earthquakes and Tsunamis,” at https://oceanexplorer.noaa.gov/explorations/03trench/trench/trench.html.
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Figure 2. Major Faults on the West Coast of North America

Source: U.S. Geological Survey, “San Andreas Fault,” at https://www.usgs.gov/media/images/san-andreas-fault-3.
Notes: The West Coast of the United States is vulnerable to earthquakes because of the major col isions
between tectonic plates. California is most vulnerable to earthquakes on the San Andreas Fault and many parallel
and branching faults (these other faults are not shown on the figure). The San Andreas Fault is caused by the
col ision of the Pacific Plate with the North America Plate (see the relative directions of motions of these plates
noted by the red arrows on the figure). The San Andreas Fault continues into Mexico, causing earthquake risks
for Mexico. Northern California, Oregon, Washington, and British Columbia, Canada, are susceptible to
earthquakes on the Cascadia Subduction Zone (labeled Subduction Zone on the figure). The Cascadia
Subduction Zone is caused by the Juan de Fuca Plate (not labeled on the figure but located between the labeled
subduction zone and the Juan De Fuca ridge) col iding and bending beneath the North America Plate.
The USGS maintains an interactive map of active faults in the United States and the USGS
Subduction Slab Model maps subduction zones around the world.25 The USGS generates and
regularly updates its Seismic Hazard Maps for the United States and its territories using these
maps and ComCat data.26 The hazard maps forecast the probability of an earthquake occurring in
a given area over a certain period of time (Figure 3). Alaska, California, Hawaii, Oregon, and
Washington face the highest probability of a damaging earthquake (i.e., reaching a shaking
intensity of VI, felt by all with slight damage to structures, on the Modified Mercalli Intensity
Scale [MMI]) over the next 100 years.27 These states face significant earthquake hazards and high

25 See the USGS “Faults,” at https://www.usgs.gov/programs/earthquake-hazards/faults. See the USGS “Slab2 - A
Comprehensive Subduction Zone Geometry Model,” at https://www.sciencebase.gov/catalog/item/
.5aa1b00ee4b0b1c392e86467 and Gavin P. Hayes et al., “Slab2, a comprehensive subduction zone geometry model,”
Science, vol. 362, no. 6410 (October 5, 2018), pp. 58-61, https://doi.org/10.1126/science.aat4723.
26 See the USGS “Seismic Hazard Maps and Specific Data,” at https://www.usgs.gov/natural-hazards/earthquake-
hazards/seismic-hazard-maps-and-site-specific-data.
27 USGS, “The Modified Mercalli Intensity Scale,” at https://www.usgs.gov/programs/earthquake-hazards/modified-
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earthquake risks because of past earthquakes, active faults, active volcanoes, and major tectonic
plate boundaries in or near these states.28
Figure 3. USGS Seismic Hazard Map
(probability of a Modified Mercalli Intensity VI earthquake in 100 years, expressed as a percentage)

Source: U.S. Government Accountability Office (GAO), Earthquakes: Progress Made to Implement Early Warning
System, But Actions Needed to Improve Program Management, GAO-21-129, March 2019.
Notes: Alaska, California, Oregon, and Washington have high earthquake probabilities (>60%) because they are
near major plate tectonic col isional boundaries. Hawaii has high earthquake probabilities because of its active
volcanoes. The Commonwealth of Puerto Rico has high earthquake probabilities because it is near a col isional
plate boundary. Idaho, Montana, Utah, and Wyoming have medium to high earthquake probabilities (20%-95%)
because of the Yellowstone volcano and the Intermountain Seismic Belt (including the Wasatch Fault) between
the Basin and Range Province and the Rocky Mountains. The New Madrid seismic zone, at the intersection of
Arkansas, Il inois, Kentucky, Missouri, and Tennessee, and parts of South Carolina surrounding Charleston have
medium earthquake probabilities (20%-60%) because of past large-magnitude (M7.0+) earthquakes that occurred
in the early to late 1800s. Little is known about the faults that caused these large earthquakes, because there is
not enough information to decipher the structure below the surface. Other states with low earthquake
probabilities (2%-20%) are vulnerable to earthquakes. Earthquakes cannot be predicted nor can the potential for
an earthquake to occur in areas with some seismic history be ruled out. For more details about New Madrid and
South Carolina, see USGS, “The New Madrid Seismic Zone,” at https://www.usgs.gov/programs/earthquake-

mercalli-intensity-scale. See the Appendix for more information about the Modified Mercalli Intensity Scale.
28 Hawaii is not near a collisional plate boundary but has very high earthquake probabilities according to the USGS
Seismic Hazard Map. Hawaii experiences earthquakes generated by the growth and activity of several volcanoes that
make up the big island of Hawaii. In addition, Hawaii is the most tsunami-prone state. Tsunamis that impact the state
can be triggered by earthquakes, landslides, or volcanic activity that occur in Hawaii or by earthquakes or volcanic
activity originating from any of the major subduction zones that form a coastal ring around the Pacific Ocean Basin.
Hawaii has experienced 135 confirmed tsunamis since 1812. Since 1923, nine tsunamis caused 294 fatalities and an
estimated $703 million in damage. International Tsunami Information Center, “Hawaii Tsunamis,” at http://itic.ioc-
unesco.org/index.php?option=com_content&view=category&id=1436&Itemid=1436.
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hazards/new-madrid-seismic-zone; and Martin C. Chapman et al., “Modern Seismicity and the Fault Responsible
for the 1886 Charleston, South Carolina, Earthquake,” Bulletin of the Seismological Society of America, vol. 106, no.
2 (February 16, 2016), at https://doi.org/10.1785/0120150221. See Appendix for more information about the
Modified Mercalli Intensity Scale.
FEMA uses the USGS earthquake probability forecasts to estimate earthquake risks in the United
States. FEMA estimates annualized building loss due to potential earthquake hazards using a
hazard model called Hazus (Figure 4).29 Building loss is a proxy for relative earthquake risk;
California, Oregon, and Washington face the greatest risks for the largest annualized building
losses based on the Hazus model. Other potential losses that are harder to estimate include
damage to roads, bridges, utilities, dams and reservoirs, power plants, mines and quarries, and
other structures, in addition to the disruption of commercial, education, government, and
nongovernment operations. In 2017, FEMA estimated the annualized earthquake loss (AEL) to
building stock was $6.1 billion and that California, Oregon, and Washington account for 73% of
AEL due to the earthquake frequency, built environment density, and population size in these
states.30 FEMA has an online tool—the National Risk Index for Natural Hazards—that estimates
the risks for different hazards, including earthquakes, in each county in every state.31 The risk
index includes expected annualized losses, social impacts, and community resilience.32 According
to this index, California, Oregon, and Washington have the highest risk index for earthquakes
across a larger area and a larger population than other states.

29 For more information about Hazus models and FEMA’s Hazus Program, see FEMA, “Hazus,” at
https://www.fema.gov/flood-maps/products-tools/hazus.
30 These estimates were prepared in 2017. See Federal Emergency Management Agency (FEMA), Hazus Estimated
Annualized Earthquake Losses for the United States, 2017, at https://www.fema.gov/sites/default/files/2020-07/
fema_earthquakes_hazus-estimated-annualized-earthquake-losses-for-the-united-states_20170401.pdf. The calculated
annual losses may be different in 2022.
31 See FEMA, “National Risk Index,” at https://hazards.fema.gov/nri/.
32 FEMA’s expected annualized loss is based on exposure of buildings, agriculture, and population to the specific
hazard times the expected annual frequency of the hazard (in this case, annual expected frequency of an earthquake,
which is based on the USGS’s probability forecasts) times the historic loss ratio (i.e., the expected loss of buildings,
agriculture, and population per earthquake). For more information, see FEMA, “Expected Annualized Losses,” at
https://hazards.fema.gov/nri/expected-annual-loss. FEMA’s national risk index for earthquakes estimates the relative
risk of a community compared with the rest of the United States for building and population losses due to an
earthquake. FEMA compiles data regarding past earthquake locations, previous occurrences, and future probabilities
from the USGS National Seismic Hazard Assessment; the Global Significant Earthquake Database produced by the
National Oceanic and Atmospheric Administration (NOAA; see NOAA, “NCEI/WDS Global Significant Earthquake
Database, 2150 BC to Present,” at https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=
gov.noaa.ngdc.mgg.hazards:G012153); and Carl W. Stover and Jerry L. Coffman, Seismicity of the United States,
1568-1989 (revised), USGS Professional Paper 1527, 1993, pp. 1-418, at https://doi.org/10.3133/pp1527.
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Figure 4. FEMA Annualized Earthquake Losses
(estimates in 2017 dollars)

Sources: ShakeAlert, “ShakeAlert: An Earthquake Early Warning System for the West Coast of the United
States,” at https://www.shakealert.org/. (ShakeAlert added details about the total loss, West Coast losses, and
population.) Original figure and calculations from the Federal Emergency Management Agency (FEMA), Hazus
Estimated Annualized Earthquake Losses for the United States, 2017, at https://www.fema.gov/sites/default/files/2020-
07/fema_earthquakes_hazus-estimated-annualized-earthquake-losses-for-the-united-states_20170401.pdf
(hereinafter FEMA, Hazus, 2017).
Notes: In the United States, FEMA estimates the total building and building content economic exposure to
earthquake hazards is $59 tril ion (all estimates presented here are based on calculations completed and
published in 2017). These earthquake losses are estimates for buildings only and do not consider the loss of life,
other property, other infrastructure, business, government, and other losses. See FEMA, Hazus, 2017. Also see
FEMA, “What Is Hazus?,” at https://www.fema.gov/flood-maps/tools-resources/flood-map-products/hazus/about.
Background and Authority to Issue Earthquake
Early Warnings
Since 1930, Congress has authorized programs and appropriated funds for earthquake research
(or seismology) to reduce earthquake risks.33 This earthquake research led to advances in the
understanding of Earth processes, improved earthquake instrumentation, and earthquake risk
reduction that has led to the development of EEW. Congress expanded earthquake research in the
1960s; the expansion focused on detecting underground nuclear explosions using seismic
instruments and finding ways to reduce earthquake risks. Congress increased appropriations to
almost $30 million (in 1959-1961 dollars) annually between 1959 and 1961 for the Department of
Defense’s Project VELA Uniform (VELA) for seismic investigations to support the detection of
underground nuclear explosions and to support cooperation among nations to detect nuclear

33 U.S. Government Accountability Office (GAO), Need for a National Earthquake Research Program, B-176621,
September 11, 1972, pp. 1-81, at https://www.gao.gov/assets/b-176621.pdf (hereinafter, GAO, National Earthquake
Research, 1972).
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weapons testing. VELA led to improved seismic instruments and seismic networks and
accelerated the sharing and standardization of seismic technology and data throughout the
world.34 These advances in research and instrumentation benefitted EEW development.
In the 1960s and the 1970s, there were damaging earthquakes in the United States and the
potential for earthquake prediction based on one “predicted” event. The 1964 M9.2 Anchorage
earthquake on the Aleutian Arc Subduction Zone, the largest event ever recorded in the United
States, caused 9 fatalities, many injuries, and extensive damage in Alaska and generated a
tsunami that caused 122 fatalities, many injuries, and damage in Alaska, Hawaii, Washington,
Oregon, and California.35 The 1971 M6.6 San Fernando earthquake caused 64 fatalities, many
injuries, and extensive damage (including damage to the lower Van Norman Dam) in Los Angeles
County.36 China evacuated people from the city of Haicheng before the damaging 1975 M7.3
Haicheng earthquake struck on February 4, 1975, saving lives. This was considered a successful
earthquake “prediction” at the time. Subsequent evaluation and additional research showed that
such an earthquake prediction could not be repeated. There are no precursor physical changes that
could be used to predict earthquakes, although research continues to try to understand what may
cause an earthquake and whether any physical changes may precede an earthquake.37
During the same time frame, Congress conducted hearings that, together with reports and
workshops from other groups, called for a coordinated federal program to research (1) earthquake
hazards and risk assessments, (2) earthquake prediction and warning of an imminent earthquake,
and/or (3) earthquake-resistant engineering.38 Congress passed the Earthquake Hazards Reduction
Act of 1977 (P.L. 95-124), which codified a coordinated program to reduce risks by considering
these three research directions. It also authorized appropriations for the program, the USGS, and
NSF.39 Congress defined earthquake prediction and earthquake warning in the House report
accompanying the 1977 act as follows: “As defined in the act, an earthquake prediction is a
prediction, in definite or probabilistic terms, of the time, place, and magnitude of an earthquake,
whereas an earthquake warning means a recommendation that normal life routines should be
changed for a time because an earthquake is believed imminent.”40

34 GAO, National Earthquake Research, 1972.
35 For more details about the earthquake and tsunami, see the USGS, “M9.2 Alaska Earthquake and Tsunami of March
27, 1964,” at https://earthquake.usgs.gov/earthquakes/events/alaska1964/.
36 For more details about the earthquake, see the USGS, “50 Years Later an Earthquake’s Legacy Continues,” at
https://www.usgs.gov/news/featured-story/disaster-helped-nation-prepare-future-earthquakes-remembering-san-
fernando.
37 For an overview of the 1975 M7.3 Haicheng earthquake prediction, see USGS, Earthquake Hazards Program,
“Repeating Earthquakes,” at https://earthquake.usgs.gov/learn/parkfield/eq_predict.php.
38 GAO, National Earthquake Research, 1972; Robert E. Wallace, Goals, Strategies, and Tasks of the Earthquake
Hazards Reduction Program, USGS, USGS Circular 701, 1974; and U.S. Congress, Senate Committee on Commerce,
Subcommittee on Oceans and Atmosphere, Earthquake Disaster Mitigation Act of 1975, 94th Cong., 2nd sess., February
19, 1976, No. 94-64, S261-3. Congressional deliberations on earthquake research for risk reduction are recorded in
many other hearings after the 1964 M9.2 Anchorage earthquake and before passage of the Earthquake Hazards
Reduction Act of 1977 (P.L. 95-124). The particular hearing referenced above covered most aspects of the
deliberations, featured witnesses and witness testimony from federal agencies, and included copies of relevant reports.
39 For more on NEHRP, see CRS Report R43141, The National Earthquake Hazards Reduction Program (NEHRP):
Issues in Brief, by Linda R. Rowan.
40 The House report that accompanied P.L. 95-124 is U.S. Congress, House Committee on Science and Technology,
Earthquake Hazards Reduction Act of 1977, Report to Accompany H.R. 6683, 95th Cong., 1st sess., H. Rept. 95-286, pt.
1, May 11, 1977.
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Earthquake prediction and warning about an imminent earthquake are not possible based on the
current understanding of Earth processes. Therefore, NEHRP’s efforts shifted to EEW beginning
in the 1980s. Congress directed the USGS to develop an automated, real-time EEW system
prototype in the 1997 reauthorization of NEHRP (P.L. 105-47). An automatic seismic hazard
warning system warns high-risk operations, such as public transit, that an earthquake has been
detected and that damaging shaking is coming to the operations’ location. This warning allows
the operations to take automated actions, such as stopping a train, to reduce risks.
In the NEHRP Reauthorization Act of 2018 (P.L. 115-307), Congress removed statutory language
requiring the USGS to develop procedures for making earthquake predictions and replaced it with
language requiring NEHRP to develop procedures to issue EEWs. The language states that the
USGS should “continue the development of the Advanced National Seismic System, including
earthquake early warning capabilities.” P.L. 115-307 requires the USGS, in the event of an
earthquake, to issue an alert and a warning, when necessary and feasible, to FEMA, NIST, and
state and local officials.
Congress authorized the President to direct federal authorities to warn the public about a disaster
in the Disaster Relief Act of 1974 (P.L. 93-288, 42 U.S.C. §5132), which was reauthorized and
renamed the Robert T. Stafford Disaster Relief and Emergency Assistance Act in 1987 (Stafford
Act; P.L. 100-707). Congress directed the President (1) to ensure agencies are able to issue
disaster warnings to state and local governments and to use federal agencies to assist states and
local officials with disaster warnings,41 (2) to make available a civilian defense warning system to
provide disaster warnings to states and the civilian population in endangered areas, and (3) to
cooperate with private or commercial communication systems to provide disaster warnings to
states and the civilian population in endangered areas. Congress authorized the President to direct
the USGS to provide warnings about earthquakes using civilian defense warning systems and to
enter into agreements to use private or commercial communication systems to provide disaster
warnings to states and civilian populations in endangered areas.42 Congress did not specify
earthquake early warnings in the Stafford Act. The USGS calls its warnings EEWs, to clarify that
they are not earthquake predictions or forecasts but are based on detecting the start of an
earthquake and then providing a warning within tens of seconds. In contrast, most severe weather
warnings provide hours to days for preparation and protective actions.43
The ShakeAlert System
ShakeAlert is the first public EEW system operating in the United States.44 A public EEW system
uses FEMA or other communication pathways to provide alerts to individuals and institutions.
ShakeAlert began sending earthquake alerts to communication providers for EEW broadcasts to
the public in California in October 2019, in Oregon in March 2021, and in Washington in May
2021. ShakeAlert is available only in these three states. ShakeAlert consists of the following
components:

41 Disaster refers to natural hazards, such as earthquake, flood, hurricane, tornado, landslide, and fire (P.L. 93-288).
42 Robert E. Wallace, Goals, Strategies and Tasks of the Earthquake Hazards Reduction Program, USGS, USGS
Circular 701, 1974.
43 See National Weather Service (NWS), “Hurricane and Tropical Storm Watches, Warnings, Advisories, and
Outlook,” at https://www.weather.gov/safety/hurricane-ww; NWS, “Understand Tornado Alerts,” at
https://www.weather.gov/safety/tornado-ww; and NWS, “Storm Prediction Center,” at https://www.spc.noaa.gov/.
44 ShakeAlert, “ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States,” at
https://www.shakealert.org/; and USGS, “ShakeAlert’” at https://earthquake.usgs.gov/data/shakealert/.
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 An earthquake-sensing network of seismic and geodetic stations
 Robust and rapid telemetry (i.e., continuous recording and transmitting of
instrument readings to data processing centers)
 Data processing centers to estimate earthquake characteristics and hazards
 Decisionmaking tools to determine if the earthquake may cause damage (i.e.,
meets shaking intensity thresholds) and to prepare alert messages
 Coordination and cooperative agreements with many communication providers
for rapid mass notification of EEWs
Previous EEW system prototypes and earlier versions of the ShakeAlert system in the United
States were experimental and sent alerts to specific testers.45 EEW system development in the
United States started in California, because of the state’s high earthquake risks, the knowledge of
California earthquake hazards, and the established seismic and geodetic networks that could
function as part of an earthquake-sensing network. Experimental EEW systems operated in
Oakland and Southern California in 1989 and 1997, respectively, as short-term tests of EEW. A
prototype EEW system called ShakeAlert began testing in California in 2012 and in the Pacific
Northwest in 2015. Congress appropriated funds for these activities primarily through the USGS
EHP and NSF research grants and cooperative agreements.46
The earthquake-sensing network detects seismic waves that radiate outward from the starting
point of an earthquake and sends earthquake-sensing instrument data to the data processing
centers (Figure 5).47 The network’s intent is to use the faster P-waves to detect the start of an
earthquake and prepare an alert before the slower, more damaging S-waves arrive at locations
further from the earthquake’s epicenter. It is not possible to provide EEW to some locations close
to the epicenter, because there is not enough time to complete the EEW process before the
shaking arrives. Data processing centers analyze the data and estimate the earthquake’s location
and magnitude, as well as the area that may receive high-intensity ground shaking. The
processing centers send the alert messages containing this information to communication
providers.

45 For a timeline of the development of EEW and ShakeAlert in particular, see Richard Allen, “Earthquake Early
Warning Milestones,” UC Berkeley, at https://rallen.berkeley.edu/research/EEWmilestones.html; and Sara K. McBride
et al., “Evidence-Based Guidelines for Protective Actions and Earthquake Early Warning Systems,” Geophysics, vol.
87, no. 1 (January-February 2022), pp. WA77-WA102, at https://doi.org/10.1190/geo2021-0222.1, Figure 2
(hereinafter McBride, “Protective Actions,” 2022).
46 USGS, ShakeAlert Plan, 2018, p. 6.
47 Body waves are seismic waves that travel through the Earth’s interior. The waves used for earthquake detection for
EEW are the primary or compression (P) waves and the secondary or shear (S) waves. P-waves, which travel faster
than S-waves, are the first seismic waves to be sensed by instruments deployed at the surface and are the first waves to
arrive at a given location. S-waves arrive later than P-waves but carry more energy and cause more intense shaking for
a longer time than P-waves. S-waves cause the most damaging ground shaking in most earthquakes that impact
communities. An effective EEW system detects the P-waves and determines the earthquake characteristics. This allows
an EEW system to provide a warning of high-intensity shaking before the S-waves arrive at locations further away
from the earthquake sensing instruments. Surface waves are seismic waves that travel along the surface of the crust;
these waves arrive later than the body waves and can contribute to damaging ground shaking, especially for structures
that may have been damaged to some extent by the earlier S-waves.
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Figure 5. Schematic of the ShakeAlert System

Source: ShakeAlert, “ShakeAlert: An Earthquake Early Warning System for the West Coast of the United
States,” at https://www.shakealert.org/.
Notes: Once an earthquake starts (star labeled epicenter and fault on the figure), the ShakeAlert earthquake-
sensing network (sensors on figure) detects the P-waves (yellow curve shows the P-wave radiating away from the
epicenter and arrow indicates the general direction of the waves) at sensors closest to the epicenter. The
sensors transmit these data to data processing centers (only one is shown on the figure, labeled Earthquake alert
center). The centers process the data and, if the earthquake may be damaging, prepare alert messages with
information about the earthquake’s magnitude and location and what areas may receive intense shaking from the
later-arriving, more damaging S-waves (red curve and arrow). Public and private communication pathways
convert the alert messages into EEWs and send them to individuals and institutions in endangered areas. On the
figure, the nearby city is in the path of the seismic waves; the goal is for everyone in the city to receive an EEW
before the S-waves reach the city and cause intense shaking.
Institutions and communication providers use the ShakeAlert-generated messages to prompt
protective actions, which reduce earthquake risks and costs (e.g., for repairs or loss of operations)
by preventing damage to people and property (Figure 6).48 Some institutions take automated
actions based on ShakeAlert messages. These automated actions are performed without any
human intervention; the ShakeAlert messages are hardwired into critical operations (i.e., through
machine-to-machine communications) and prompt automatic protective actions based on the
message details. Automated actions may include stopping or slowing trains, opening fire station
doors, stopping elevators at a floor and opening elevator doors, preventing vehicles from entering
bridges or tunnels, and other actions.49
In addition, communication providers use ShakeAlert-generated messages to reduce earthquake
risks by transmitting EEWs (Figure 6). Emergency communication providers, such as FEMA
communication pathways or cell phone EEW applications (apps), receive the ShakeAlert
messages and send EEWs to individuals in high-risk areas. These EEWs include the
recommended protective action: Drop, Cover, and Hold On (DCHO).50 Table 1 lists some other

48 Strauss, “Benefits,” 2016.
49 For example, automatically slowing or stopping a train is one of the most common protective actions to take for an
EEW, because the potential to avoid a derailment outweighs the minimal delays caused by stopping a train. EEW
systems continue to develop automated or semiautomated alerting for critical structural systems where the application
is relatively simple and the cost-benefit calculations and risk-reduction potential are significant.
50 Drop, Cover, and Hold On (DCHO) is the recommended protective action for an individual on the West Coast
because (1) most injuries and fatalities are caused by falling on structures (e.g., stairs), tripping on damaged structures
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examples of automated or individual protective actions that may be taken after receiving an EEW
to reduce risks.
Figure 6. ShakeAlert System from Detection to Protection

Source: ShakeAlert, “Graphics Library,” at https://www.shakealert.org/messaging_toolkit/graphics-library/.
Table 1. Examples of Protective Actions That May Be Taken After Receiving an
Earthquake Early Warning
Sector
Sample Protective Action(s)
Construction
Placing cranes and lifts in safe positions and moving people away from hazardous
construction sites.
Emergency
Alerting first-responders in the field to temporarily retreat to safe spaces, opening doors for
Management
emergency vehicles, and starting generators.
General
Alerting the public to prepare physically and psychologically for the impending shaking.
Industrial
Closing valves, slowing or stopping production lines and sensitive processes, and moving
people away from hazardous industrial processes.
Medical
Halting dental operations, surgeries, laser procedures, and other medical procedures.
Office
Stopping elevators at the nearest floor and opening their doors, allowing people to move
away from windows to interior/safer spaces.
Restaurants
Turning off heat sources and securing or avoiding areas with potentially dangerous
equipment, such as deep fryers.

or fallen objects, and/or being hit by falling objects during intense shaking, and DCHO reduces these risks; (2) many
structures are built to earthquake-resistant standards in high-risk regions on the West Coast, so the structures should not
collapse, making DCHO more effective than evacuation; and (3) individuals are most likely to be inside a structure
when an earthquake occurs (i.e., Americans spend most of their time indoors), so DCHO is the most likely situational
reaction. Most injuries and fatalities from earthquake hazards occur when people are harmed by damaged structures
and infrastructure lifelines. See McBride, “Protective Actions,” 2022. For a list of actions to take before, during, and
after an earthquake, including a description of DCHO, see FEMA, “Ready, Earthquakes,” at https://www.ready.gov/
earthquakes; and Occupational Safety and Health Administration, “Earthquakes Guide,” at https://www.osha.gov/
emergency-preparedness/guides/earthquakes.
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Sector
Sample Protective Action(s)
Schools
Warning students and staff to take a protective action such as Drop, Cover, and Hold On.
Transportation
Slowing or stopping trains, stopping aircraft takeoffs and landings, closing vulnerable bridges,
and slowing or stopping traffic by turning all traffic signals to red.
Utilities
Opening or closing critical valves in pipelines, shutting down systems, rerouting power
supplies, and moving field personnel into safer positions (i.e., places not exposed to power
lines or other hazardous conditions).
Vehicles
Instructing alerted drivers to turn on emergency flashers (to warn others) and to slow
down.
Source: ShakeAlert, “FAQ,” at https://www.shakealert.org/faq/. Modified by CRS.
The ShakeAlert system is a cooperative project led by the USGS, with many partners that are
responsible for the system’s research and development, operations and maintenance, and/or
education and outreach (Table 2). These partners include state agencies, universities, and
nonprofit organizations that operate NSF facilities. The USGS considers ShakeAlert to be part of
the Advanced National Seismic System (ANSS) within the EHP.51 The USGS prepared a revised
implementation plan for ShakeAlert in 2018, which summarized the science, technology, and
implementation of ShakeAlert and how the USGS aims to improve the EEW system.52
FEMA and NSF indirectly support aspects of ShakeAlert (i.e., Congress does not appropriate
funds to these federal agencies specifically for ShakeAlert activities). FEMA provides
communication pathways to deliver EEWs to the public and conducts earthquake risk
assessments. In addition, Congress authorized FEMA to award hazard mitigation grants to
improve ShakeAlert’s earthquake-sensing network. Section 1233 of the Disaster Recovery
Reform Act of 2018 (Division D of the Federal Aviation Administration Reauthorization Act of
2018, P.L. 115-254) authorized FEMA to provide hazard mitigation assistance through the Hazard
Mitigation Grant Program and the Building Resilient Infrastructure and Communities Program
for activities that reduce earthquake risk and build EEW capability.53 FEMA may support
improvements to seismic and geodetic networks that are part of ShakeAlert and the purchase and
installation of seismometers, GNSS receivers, and associated infrastructure (e.g., telemetry and
signal processing) that are part of the ShakeAlert system.54
NSF supports earthquake research and earthquake-sensing network operations and maintenance.
It does so through research grants to universities and cooperative agreements with seismic or

51 The Advanced National Seismic System (ANSS) supports basic and applied research to understand and define the
structure of the Earth beneath the surface, including mapping faults and understanding earthquakes. ANSS activities
contribute to the research and development of EEW. ANSS consists of a backbone network of almost 100 seismic
stations distributed throughout the United States, the USGS National Earthquake Information Center, the National
Strong Ground Motion network, and 15 regional seismic networks. See the USGS, “ANSS – Advanced National
Seismic System,” at https://www.usgs.gov/programs/earthquake-hazards/anss-advanced-national-seismic-system.
52 USGS, ShakeAlert Plan, 2018.
53 FEMA, “Hazard Mitigation Assistance Grants,” at https://www.fema.gov/grants/mitigation; and FEMA, “Building
Resilient Infrastructure and Communities,” at https://www.fema.gov/grants/mitigation/building-resilient-infrastructure-
communities.
54 FEMA mitigation grants may not support any operations and maintenance activities for ShakeAlert. FEMA may
support only improvements to ShakeAlert, because the authorization requires FEMA to support EEW capabilities that
enable end-user notification. FEMA consulted with the USGS and determined that ShakeAlert is the only system that
enables end-user notification. FEMA, “Disaster Recovery Reform Act and Earthquake Early Warning Systems,” fact
sheet, September 30, 2020, at https://www.fema.gov/sites/default/files/2020-09/fema_drra-earthquake-early-warning-
systems_fact-sheet_September-2020.pdf.
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geodetic facilities (e.g., the Seismological Facilities for the Advancement of Geoscience, operated
by the Incorporated Research Institutions for Seismology; the Geodetic Facilities for the
Advancement of Geoscience, operated by UNAVCO Inc.; and the Southern California
Earthquake Center, operated by the University of Southern California).55 The National
Aeronautics and Space Administration (NASA) supports the use of geodetic tools for earthquake
and tsunami research and for hazards warning and mitigation.56
Table 2. ShakeAlert Nonfederal Partners
Institutional Partners Involved in ShakeAlert Research and Development, Operations and
Maintenance, and/or Education and Outreach
California Geological Survey (CGS)
California Governor’s Office of Emergency Services (Cal OES)
California Institute of Technology (Caltech)
Central Washington University (CWU)
Incorporated Research Institutions for Seismology (IRIS)
Oregon Department of Geology and Mineral Industries (DOGAMI)
Oregon Military Department, Office of Emergency Management (OEM)
Southern California Earthquake Center (SCEC)
Swiss Seismological Service of ETH Zurich
UNAVCO Inc.
University of California, Berkeley (UCB)
University of California, San Diego
University of Nevada, Reno
University of Oregon (UO)
University of Washington (UW)
Washington Military Department, Emergency Management Division (WMD)
Washington State Department of Natural Resources
Sources: USGS, ShakeAlert Plan, 2018; USGS, “Earthquake Early Warning – Overview,” at https://www.usgs.gov/
programs/earthquake-hazards/science/earthquake-early-warning-overview#partners; and ShakeAlert,
“ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States,” at
https://www.shakealert.org/.
Notes: ETH Zurich stands for Eidgenössische Technische Hochschule Zürich in German (Swiss Federal Institute of
Technology in Zürich, in English).

55 IRIS, “Seismological Facility for the Advancement of Geoscience (SAGE),” at https://www.iris.edu/hq/sage;
UNAVCO, “GAGE Facility,” at https://www.unavco.org/what-we-do/gage-facility/; and Southern California
Earthquake Center (SCEC), “About the Center,” at https://www.scec.org/about.
56 National Research Council, Precise Geodetic Infrastructure: National Requirements for a Shared Resource
(Washington, DC: National Academies Press, 2010), at https://doi.org/10.17226/12954 (hereinafter NRC, Precise
Geodetic Infrastructure, 2010); and NASA, Earth Science, Applied Sciences, “Supporting Earthquake Response and
Recovery,” at https://appliedsciences.nasa.gov/what-we-do/disasters/earthquakes.
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Earthquake-Sensing Network
The ShakeAlert earthquake-sensing network consists of 1,309 seismic stations and about 1,100
geodetic stations in California, Oregon, and Washington (Figure 7 and Figure 8) as of February
2022.57 Most of these seismic and geodetic stations existed prior to ShakeAlert operations as part
of regional networks for research, hazard assessment, natural resource management, and other
purposes (Table 3). Some stations in these networks now serve an additional purpose: detecting
the start of an earthquake to provide EEW. The USGS and ShakeAlert partners aim to add more
seismic stations and upgrade more geodetic stations to improve earthquake detection on the West
Coast.58
ShakeAlert uses diverse telemetry technology, including cellular modem, microwave, and radio,
to transmit data from seismic or geodetic stations to data processing centers.59 The telemetry
technology depends on the station location and technology and on the available telemetry
systems. In California and Oregon, some stations use their respective state microwave telemetry
systems to transmit data. In California, the USGS connected the USGS microwave telemetry
systems between Northern and Southern California. The California Governor’s Office of
Emergency Services (Cal OES) Public Safety Communications system and the University of
California, Berkeley, ShakeAlert data processing center are connected with a dedicated telemetry
system. The USGS and ShakeAlert partners aim to improve and optimize telemetry for the
earthquake-sensing network to support robust and rapid data delivery from the seismic and
geodetic stations to the data processing centers under all circumstances.60 These stakeholders are
investigating other telemetry options, including whether new technologies such as the First
Responder Network Authority (FirstNet) or a satellite-based data transfer system operated by
Starlink may improve telemetry. 61

57 Correspondence between CRS and USGS, April 18, 2022.
58 The USGS aims to add 366 more seismic stations and upgrade 176 geodetic stations to provide adequate coverage
and station density to detect earthquakes rapidly and accurately in California, Oregon, and Washington. ShakeAlert
Plan, 2018; and correspondence between CRS and the USGS, April 18, 2022.
59 USGS, ShakeAlert Plan, 2018.
60 USGS, ShakeAlert Plan, 2018; and correspondence between CRS and the USGS, January 12, 2022.
61 USGS, ShakeAlert Plan, 2018. FirstNet is an independent authority within the U.S. Department of Commerce,
National Telecommunications and Information Administration, that provides a dedicated communications network for
emergency responders and the public safety community. Chartered in 2012, FirstNet’s mission is to ensure the
building, deployment, and operation of the nationwide broadband network that equips first responders to save lives and
protect U.S. communities. See FirstNet, “FirstNet Authority,” at https://www.firstnet.gov/. See also CRS Report
R45179, The First Responder Network (FirstNet) and Next-Generation Communications for Public Safety: Issues for
Congress, by Jill C. Gallagher. Starlink is a commercial company that supports high data rate activities using low Earth
orbit satellites. See Starlink, “Starlink,” at https://www.starlink.com/.
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Table 3. Regional Networks That Contribute to ShakeAlert
Number of Stations
Network Name:
Contributing to
Location
Partners
Funding Sources
ShakeAlert
California Integrated
California Institute of
USGS and Cal OES
>832
Seismic Network: CAa
Technology; University of
California, Berkeley;
California Geological
Survey; Cal OES; and
USGS
Pacific Northwest Seismic
University of Oregon,
USGS, Department of
>283
Network: OR and WAb
University of Washington, Energy, State of
IRIS, UNAVCO Inc., and
Washington, and State of
USGS
Oregon
Network of the Americas
UNAVCO Inc.
NSF, NASA, and USGS
>500
(Geodetic): CA, OR, and
WAc
Pacific Northwest
Central Washington
NSF, NASA, and USGS
>100
Geodetic Array: OR and
University
WAd
Bay Area Regional
University of California,
USGS
33
Deformation Network
Berkeley; California
(Geodetic): Northern
Institute of Technology;
CAe
University of Washington;
Central Washington
University; Lawrence
Berkeley National
Laboratory; and USGS
USGS Pasadena Office
USGS
USGS
140
(Geodetic): Southern CAf
USGS Menlo Park Office
USGS
USGS
8
(Geodetic): Northern CAf
Source: USGS, ShakeAlert Plan, 2018.
Notes: Cal OES = California Governor’s Office of Emergency Services; IRIS = Incorporated Research
Institutions for Seismology; NASA = National Aeronautics and Space Administration; NSF = National Science
Foundation; USGS = U.S. Geological Survey.
a. California Integrated Seismic Network, “CISN,” at https://www.cisn.org/,
b. Pacific Northwest Seismic Network, “PNSN,” at https://pnsn.org/,
c. UNAVCO, “Network of the Americas,” at https://www.unavco.org/projects/major-projects/nota/nota.html,
d. Central Washington University, “Pacific Northwest Geodetic Array,” at https://www.geodesy.cwu.edu/
e. Berkeley Seismology Lab, “Bay Area Regional Deformation Network,” at https://seismo.berkeley.edu/bard/
f.
USGS, “USGS Real-Time Deformation Monitoring,” at https://www.socalgeodetic.org/.
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Figure 7. Seismic Stations Contributing to ShakeAlert as of February 2022
(established and planned seismic stations)

Source: USGS, April 18, 2022.
Notes: ShakeAlert’s earthquake-sensing network consists of 1,309 seismic stations (blue dots). The USGS and
ShakeAlert partners aim to add 366 seismic stations to the ShakeAlert network (yellow squares). These added
stations wil be either new stations or upgrades to existing stations in regional networks. The map is from the
USGS. Correspondence between CRS and USGS on April 18, 2022.
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Figure 8. Geodetic Stations Contributing to ShakeAlert as of February 2022

Source: USGS, April 18, 2022.
Notes: ShakeAlert’s earthquake-sensing network includes about 1,100 geodetic stations. The red dots indicate
geodetic stations that were not transmitting data when the figure was prepared in February 2022. The USGS and
ShakeAlert partners aim to upgrade 176 geodetic stations (not shown on the figure) and add them to the
earthquake-sensing network. Mapped faults are delineated by black lines, excluding the state boundaries. The
map is from the USGS. Correspondence between CRS and USGS on April 18, 2022.
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Data Processing, Analysis, and Alert Message Generation
The seismic and geodetic stations in the ShakeAlert network operate continuously and
autonomously. Every second, the stations send real-time data to the data processing centers for
analysis. The more stations that detect an earthquake starting at about the same time, the more
accurate and rapid the earthquake estimate. ShakeAlert uses the seismic data to detect an
earthquake, estimate its characteristics, and determine whether to develop and send alert
messages. The USGS and ShakeAlert partners aim to integrate geodetic data into the data
analysis system to provide a more effective EEW.62 As of April 2022, the geodetic data was being
transmitted to the testing and development platform at the data processing centers and was used
for earthquake analysis on this testing platform.63 ShakeAlert uses four processing centers to help
provide redundancy and reliability. These centers are in Pasadena, CA (operated by the USGS and
the California Institute of Technology); Menlo Park, CA (operated by the USGS); Berkeley, CA
(operated by the USGS and the University of California, Berkeley); and Seattle, WA (operated by
the USGS and the University of Washington). The Berkeley processing center does not deliver
ShakeAlert messages to communication providers.64
ShakeAlert can generate three types of alert messages with earthquake information for
communication providers: (1) location and magnitude; (2) location, magnitude, and a contour
map of the area that may receive intense shaking; and (3) location, magnitude, and a gridded map
of the area that may receive intense shaking. Providers may subscribe to the message type or
types they want to use.65
Communication of Earthquake Early Warnings
Once communication providers receive the ShakeAlert-powered alert messages, the providers use
various communication pathways (e.g., cell phones, public address systems, or machine-to-
machine communications) to deliver EEWs to individuals and institutions. Generally, distributing
ShakeAlert messages over different communication pathways increases the chance that people
may receive and act on the alerts.66 The Stafford Act required the USGS to ensure ShakeAlert-
powered alert messages are encoded in such a way that they can be sent as EEWs through the

62 USGS, ShakeAlert Plan, 2018, p. 7. The geodetic stations add more spatial coverage by adding more earthquake-
sensing stations to the system. The geodetic data may help detect the largest magnitude (M7+) earthquakes on
subduction zones more accurately and more rapidly than the seismic data alone. For example, Japan’s EEW system
underestimated the 2011 M9.1 Tohoku earthquake as an M8.0 partly because of a lack of seismic data near the event
and because the system did not use the geodetic data (i.e., the underestimate was significant because an M8.0 is a far
less energetic event then an M9.1; see Appendix for more information about magnitude and earthquake energy). A
post-event analysis indicated that using the real-time geodetic data would have produced a more accurate and higher-
magnitude event estimate, leading to a larger tsunami estimate and a larger area to warn. Allen and Melgar, “EEW
Advances,” 2019; and NRC, Precise Geodetic Infrastructure, 2010, p. 48.
63 Based on research, development, and testing, the data analysis may be improved by adding the raw geodetic data and
the Geodetic First Approximation of Size and Timing—Peak Ground Displacement algorithm into the operational data
analysis system. See Jessica R. Murray et al., “Development of a Geodetic Component for the U.S. West Coast
Earthquake Early Warning System,” Seismological Research Letters, vol. 89, no. 6 (October 3, 2018), pp. 2322-2336,
at https://doi.org/10.1785/0220180162.
64 USGS, ShakeAlert Plan, 2018.
65 USGS, ShakeAlert Plan, 2018, pp. 18-20.
66 See National Academies of Sciences, Engineering, and Medicine, Emergency Alert and Warning Systems: Current
Knowledge and Future Research, 2018, at https://doi.org/10.17226/24935.
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FEMA Integrated Public Alert Warning System (IPAWS) and to make available ShakeAlert-
powered messages to non-FEMA communication providers for distribution as EEWs.67
Rapid EEW is intended to provide individuals and institutions tens of seconds to minutes to
prepare before intense shaking reaches their location, depending on their distance from the
earthquake’s epicenter (see Table 1).68 ShakeAlert aims to deliver alert messages in about 4-20
seconds of the earthquake’s origin time, depending on the earthquake’s characteristics and the
station density near the event.69 The USGS requests that communication providers deliver EEWs
to specific areas within seconds and aims for any delays in delivery to be less than five seconds.70
Geotargeting (i.e., sending EEWs to specific areas) is intended to help reach only those affected
by the event; increase confidence in EEWs; limit the strain on commercial communication
systems, which may become overwhelmed or limited in the event of an emergency; reduce
alerting fatigue; and improve response.71 In addition, ShakeAlert sets minimum thresholds of
magnitude and shaking intensity levels for sending an EEW to allow various communication
pathways to limit the EEWs to potentially damaging earthquakes only (Figure 9).72

67 For more details about the Integrated Public Alert Warning System, see FEMA, “Integrated Public Alert and
Warning System,” at https://www.fema.gov/emergency-managers/practitioners/integrated-public-alert-warning-system.
68 Some individuals or institutions that are close to the earthquake’s epicenter may receive no warning or preparation
times of less than 10 seconds, which is not enough time to take action. Other individuals or institutions that are far from
the earthquake’s epicenter may receive one to two minutes of preparation time. For example, many of the most
damaging earthquakes in Mexico start on the offshore subduction zone near the western coastline and are hundreds of
miles away from large cities. When a subduction zone earthquake is detected on the west coast, Mexico City receives
an EEW before the seismic waves travel hundreds of miles to the city, so that people in the city have one to two
minutes to prepare for intense shaking to arrive. USGS, Expected Warning Times, 2021; Sarah E. Minson et al., “The
Limits of Earthquake Early Warning: Timeliness of Ground Motion Estimates,” Science Advances, vol. 4, no. 3 (2018),
at https://doi.org/10.1126/sciadv.aaq0504 (hereinafter Minson, “Limits of EEW,” 2018); and Gerardo Suarez et al., “A
Dedicated Seismic Early Warning Network: The Mexican Seismic Alert System (SASMEX),” Seismological Research
Letters, vol. 89, no. 2A (March/April 2018), pp. 382-391, at https://doi.org/10.1785/0220170184 (hereinafter
SASMEX, 2018).
69 USGS, Expected Warning Times, 2021, p. 3.
70 ShakeAlert, “Become a ShakeAlert System Partner,” at https://www.shakealert.org/implementation/partners/.
71 USGS, ShakeAlert Plan, 2018.
72 USGS, ShakeAlert Plan, 2018, pp. 20-21; and Minson, “Limits of EEW,” 2018.
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Figure 9. Alert Communication Pathways and Minimum Thresholds

Source: USGS, “Earthquake Early Warning Overview,” at https://www.usgs.gov/programs/earthquake-hazards/
science/earthquake-early-warning-overview.
Notes: ShakeAlert sets minimum magnitude and Modified Mercal i Intensity Scale (MMI; shaking intensity) levels
for sending alerts from communication providers as EEWs to people or machines (magnitude threshold and
shaking intensity threshold listed above in the right columns). If the earthquake is significant enough to meet
these minimum thresholds and thus may cause damage, alerts can be sent as EEWs via five main communication
pathways (listed in the left column). The wireless emergency alert (WEA) is a FEMA technology and the USGS
sends EEW using this technology. See Appendix for more information about magnitude and the MMI shaking
intensity levels.
ShakeAlert uses five different communication pathways to send alerts: four to alert people and
one to alert systems and machines. The system sets minimum magnitude and shaking intensity
(i.e., MMI) levels for sending alerts as EEWs, and the magnitude and MMI minimum thresholds
differ for the five different communication pathways (Figure 9). ShakeAlert communicates
EEWs to individuals via four pathways:
 FEMA Wireless Emergency Alert (WEA) technology to WEA-capable wireless
devices
 Cell phone apps to cell phones
 Android operating system software to Android-based cell phones
 Institutional communication pathways (e.g., public address systems in a school or
large office building) to individuals working or gathering in these places
ShakeAlert messages are communicated directly to systems and machines through a fifth
pathway: established machine-to-machine communication systems. This automated
communication allows institutions, such as public transit systems, to take automated protective
actions (Figure 9).
The amount of time to communicate EEWs via the different communication pathways varies. The
fastest machine-to-machine systems and cell phone apps via Wi-Fi or cellular networks
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communicate EEWs in as little as one second, whereas WEA technology communicates the alerts
within several tens of seconds, if at all.73 The amount of time to communicate EEWs through
institutional communication pathways (e.g., public address announcements or institutional
systems, such as email and cell phones in buildings) also varies. The fastest alerts are via
institutional services connected to Wi-Fi networks (e.g., cell phones or public address systems on
Wi-Fi), which can deliver EEWs in a few seconds in some cases.74
FEMA Communication Pathways
FEMA delivers public alerts about many hazards or other dangerous situations (e.g., Imminent
Threat Alerts) to individuals in targeted locations through IPAWS (Figure 10); these alerts
provide secure, authenticated emergency and lifesaving information sent by an authorized alerting
authority (e.g., state police, local sheriff, National Weather Service, or the USGS).75 Authorized
alerting authorities, once approved by FEMA, purchase FEMA-approved software, which they
use to send alerts that comply with FEMA standards (e.g., FEMA’s Common Alerting Protocol
and Federal Communications Commission [FCC] rules). FEMA must authenticate alerts, such as
EEWs, before they are distributed, which could lengthen the delivery time. FEMA distributes the
alerts through many communication pathways simultaneously to the area specified by the alerting
authority.
Using WEA technology, cellular carriers send alerts over their cellular networks to cell phone
users within the targeted area. Cellular carriers AT&T, T-Mobile, and Verizon voluntarily
participate in FEMA’s WEA program. One benefit of WEA technology is that people need not
subscribe to the service; carriers send EEWs to all cell phones operating in the affected area. A
challenge with the technology is that it is built into the device’s hardware and is not accessible to
cell phone app developers, which makes it difficult to upgrade or use with another app.
ShakeAlert is currently using only WEA technology to communicate EEWs among the many
IPAWS communication pathways (Figure 10). The USGS prepares a FEMA-encoded and FCC-
approved EEW that states “Earthquake Detected! Drop, Cover, Hold On. Protect Yourself. –
USGS ShakeAlert.” FEMA sends these USGS-prepared EEWs to specified locations via cellular
networks to wireless devices, such as cell phones.
The USGS proposed some changes to cell phone communications that the FCC approved,
including extending alert messages from 90 characters to 360 characters, allowing uniform
resource locators (URLs) in messages, sending Spanish language messages, and geotargeting.76
These new capabilities often require upgrades to all elements of the alerting system. In 2021, the
FCC reported that most cell phones in use can receive WEA messages but some cannot (mainly
older phones). Some of these WEA-capable phones can receive the longer 360-character

73 EEWs distributed via WiFi or cellular networks commonly arrive in 1-10 seconds, but various apps are still testing
the scaling to large numbers of users. WiFi technology uses radiofrequency waves to transmit information wirelessly.
WiFi networks work only within a limited distance and require a modem connected to a wireless router or wireless
gateway. Cellular networks use cellular signals to transmit information. Cellular networks work over larger distances
where there are enough cellular towers to transmit the cellular signals from towers to devices. The WEA system can
deliver EEWs as fast as 4 seconds based on recent tests, but many individuals receive the EEWs after more than 10
seconds or not at all. USGS, ShakeAlert Plan, 2018; and USGS, Expected Warning Times, 2021, p.3.
74USGS, Expected Warning Times, 2021, p. 3.
75 See FEMA, “Wireless Emergency Alerts,” at https://www.fema.gov/emergency-managers/practitioners/integrated-
public-alert-warning-system/public/wireless-emergency-alerts. See FEMA’s IPAWS website at https://www.fema.gov/
emergency-managers/practitioners/integrated-public-alert-warning-system.
76 USGS, ShakeAlert Plan, 2018.
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messages and Spanish language messages; a subset of those cell phones can receive the enhanced
geotargeted alerts.77 Further, the FCC found that older WEA-capable alerts had a lower reception
rate when FEMA issued a nationwide test alert.78 Thus, more people may benefit from WEA
alerts and EEWs when they upgrade to new, more advanced technologies. In addition, more
precise geotargeting may conserve communication bandwidth in an emergency, when
communication systems may be overwhelmed or damaged.79
Figure 10. FEMA Communication Pathways

Source: USGS, ShakeAlert Plan, 2018; and FEMA, “Integrated Public Alert and Warning System,” at
https://www.fema.gov/emergency-managers/practitioners/integrated-public-alert-warning-system.
Notes: The FEMA Integrated Public Alert and Warning System (IPAWS) OPEN gateway delivers alerts in two
main directions. To the left, IPAWS delivers Common Alerting Protocol (CAP)-compliant messages to the
authorities listed. To the right, IPAWS delivers alerts to the public via the communication pathways listed under
alert disseminators. People receive these alerts on the devices listed in the far right column. Canada’s Multi-
Agency Situational Awareness System (MASAS) is interoperable with IPAWS and other communication pathways
(see Canada’s “Welcome to the MASAS Exchange,” at https://www.canops.org/masas). Canada and the United
States aim to cooperate on EEWs that impact both countries.
Other Communication Pathways
The USGS has agreements with institutions to deliver EEWs using the ShakeAlert messages. The
USGS has License to Operate (LtO) partners that are licensed to use the ShakeAlert-powered

77 The more advanced geotargeted alerts require providers that participate in the WEA program to send alerts to the
targeted area with no more than a 0.1 mile overshoot. Federal Communications Commission, Report: August 11, 2021,
Nationwide WEA Test—Wireless Emergency Alerts, December 2021, at https://www.fcc.gov/document/fcc-releases-
report-nationwide-wea-test, p.5 (hereinafter FCC, WEA Test, 2021).
78 FCC, WEA Test, 2021.
79 USGS, ShakeAlert Plan, 2018, pp. 23-24.
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alert messages, following rules and guidelines set by the USGS.80 The partners can send EEWs
only for earthquakes that meet or exceed the minimum magnitude and shaking intensity
thresholds set by ShakeAlert (see Figure 9).81 In addition, the partners must communicate the
EEWs rapidly, preferably with delays of less than five seconds.82 LtO partners use the ShakeAlert
messages to create and distribute EEWs via cell phones, internet, radio, television, public address
systems, machine-to-machine communication for critical operations, and other means (Table 4).83
As of December 2021, ShakeAlert had 11 LtOs that provided products and services at more than
50 locations.84 Approximately 20 other organizations are pursuing pilot projects that may result in
LtOs.85
Table 4. ShakeAlert License to Operate Partners, as of 2021
License to Operate
ShakeAlert-Powered Alerts
Sector(s) of Operation
Partner
Communication Services
Early Warning Labs LLC
EEWs delivered to individual cell phones
Education, Emergency Management,
via the QuakeAlertUSA application (app) Health Care, Mass Notification,
in California and Oregon. EEWs
Municipal and Residential Buildings,
delivered with machine-to-machine
and Transportation
automated systems via public address
systems, automated opening of parking
garages and firehouse doors, and other
services.
Everbridge
Situational awareness notification that an Public Safety and Response
earthquake has occurred on the West
Coast (not an EEW) sent to staff in
Public Safety Answering Point facilities in
California and Oregon.
Global Security
EEWs encoded in commercial FM radio
Mass Notification
Systems/ALERT FM
to purpose-built devices.
Google
EEWs delivered to individual Android
Mass Notification
cell phones via the Android Earthquake
Alerts app in California, Oregon, and
Washington.
MetroLink/Rail Pros – Los
EEWs delivered with machine-to-
Transportation
Angeles Metropolitan Area
machine automated systems via
Transit
integration with positive train control
systems.
RH2 Engineering
EEWs delivered with machine-to-
Utilities (water)
machine automated systems integrated
with water and sewage system controls.

80 ShakeAlert, “ShakeAlert License to Operate Partners,” at https://www.shakealert.org/implementation/lto/.
81 See Appendix for a description of the magnitude and shaking intensity scales used for EEW.
82 ShakeAlert, “Become a ShakeAlert System Partner,” at https://www.shakealert.org/implementation/partners/.
83 ShakeAlert, “ShakeAlert License to Operate Partners,” at https://www.shakealert.org/implementation/lto/.
84 The major transportation companies that are License to Operate (LtO) partners using ShakeAlert are San Francisco
Bay Area Rapid Transit (BART), with 411,000 average weekday passengers (pre-COVID); Los Angeles Metropolitan
Transit Authority (LA Metro), with an average weekday ridership of 344,176; and the Southern California Regional
Rail Authority (Metrolink), which averages about 40,000 boardings on a typical weekday. Correspondence between
CRS and the USGS, January 12, 2022.
85 Correspondence between CRS and the USGS, January 12, 2022.
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San Francisco Bay Area
EEWs delivered with machine-to-
Transportation
Rapid Transit District
machine automated systems integrated
(BART)
with positive train control systems.
SkyAlert
EEWs delivered with machine-to-
Emergency Management
machine automated systems via public
address systems and SkyAlert wireless
devices for audio and visual EEWs.
University of California,
EEWs delivered to individual cell phones
Mass Notification
Berkeley/MyShake
via the MyShake app in California,
Oregon, and Washington.
Valcom
EEWs delivered with machine-to-
Education
machine automated systems integrated
with public address systems.
Varius, Inc.
EEWs delivered with machine-to-
Utilities (water), Education
machine automatic response integrated
with water and sewage system controls.
Sources: USGS, January 12, 2022; ShakeAlert.org; and USGS, ShakeAlert Plan, 2018. Modified by CRS.
At this point, cell phone apps connected to Wi-Fi or cellular networks are the most common and
effective nonfederal communication pathways to warn individuals of the approach of intense
ground shaking with enough time to take protective action. Three LtO partner organizations and
one state agency have approved cell phone apps to send ShakeAlert-powered EEWs through four
apps:
1. Google’s Android Earthquake Alerts (based on the Android operating system),
which sends ShakeAlert-powered EEWs to Android-based cell phones in
California, Oregon, and Washington (about 15.6 million devices)86
2. MyShake, available in California, Oregon, and Washington and developed by the
University of California, Berkeley (about 1.6 million downloads to devices)87
3. QuakeAlertUSA, available in California and Oregon, developed by Early
Warning Labs (about 118,000 downloads to devices)88
4. ShakeReadySD, developed by San Diego County, which integrates the
ShakeAlert-powered alert messages into the county’s SD Emergency
preparedness app (about 30,000 downloads to devices)89

86 Google developed the Android Earthquake Alerts app, which works in two ways. In California, Oregon, and
Washington, the app uses ShakeAlert messages to prepare and send EEWs to Android-based cell phones. Google is a
ShakeAlert LtO partner and follows the guidelines set by the license agreement in those states. Beyond the ShakeAlert
system, Google’s app uses Android-based cell phone data to send EEWs in other countries. See Google’s overview of
Android Earthquake Alerts at Google, “Earthquake Detection and Early Alerts, Now on Your Android Phone,” blog
post, April 11, 2020, at https://blog.google/products/android/earthquake-detection-and-alerts/. For more information
about how the app works, see Business World, “Google Launches Android Earthquake Alerts System,” June 17, 2021,
at https://www.bworldonline.com/technology/2021/06/17/376367/google-launches-android-earthquake-alerts-system/.
87 See University of California, Berkeley, “MyShake,” at https://myshake.berkeley.edu/.
88 See Early Warning Labs, “Now Live in California and Oregon,” at https://earlywarninglabs.com/mobile-app/.
89 See ReadySanDiego, “SD Emergency App,” at https://www.readysandiego.org/SDEmergencyApp/. The number of
downloads for the different apps and the estimate of Android-based devices are from correspondence between CRS and
the USGS, January 12, 2022.
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Performance: Speed and Accuracy of Earthquake Detection and
Alert Messaging
Between October 2019 and December 2021, ShakeAlert provided alert messages for 51
earthquakes.90 Most of the earthquakes were in California, and all of them were below an M6.2
and caused only mild shaking. Accurate alerts were prepared within 5 seconds of the earthquake’s
origin time in the best-case scenarios and within 6-20 seconds in other scenarios.91 ShakeAlert
met its performance metrics of accurate and timely alert messages where the seismic station
density of the network was sufficient (i.e., there was enough seismic data to rapidly and
accurately estimate the earthquake characteristics and shaking intensity and to prepare alert
messages).
The ShakeAlert system experienced some issues during the October 2019-December 2021 period.
Of the 51 public alerts issued, 2 were false alerts with inaccurate magnitude and/or location. In
addition, the system mislocated and underestimated a July 8, 2021, M6.2 earthquake about 39
miles southeast of South Lake Tahoe, resulting in confusion and under-alerting of the shaking
intensity in the area impacted by the event (i.e., alerts were not sent to people who experienced
ground shaking within the threshold of the EEW system).92 The earthquake detection was
inaccurate because the earthquake was near the edge of the network, where the seismic station
density was sparse and inadequate. Further, during this period, ShakeAlert missed five
earthquakes (located either in Mexico or offshore, where the earthquake-sensing network was not
adequate to detect the event) and sent one false alert for a non-earthquake event.93
Communication Pathways Performance: Delivery of Earthquake
Early Warnings
ShakeAlert messages for the 51 earthquakes detected between October 2019 and December 2021
were delivered as EEWs to individuals and institutions via multiple communication pathways
(Figure 9). Machine-to-machine communication pathways, many of which are hardwired to
ShakeAlert, and other pathways that use Wi-Fi or cellular networks (including many cell phone
apps) generally delivered the alert messages within a few seconds. In general, these
communication pathways met the USGS’s objective of getting EEWs to individuals and
institutions so they had enough time to take protective actions before the intense shaking arrived
at their locations.
The USGS issued 11 EEWs via FEMA WEA technology for M5.0+ events between October 2019
and December 2021 (i.e., 11 of the 51 ShakeAlert-detected earthquakes were of M5.0 or larger).
Eight of these WEA warnings were sent without delay, and three warnings were not sent due to

90 ShakeAlert, “Post ShakeAlert Message Summaries,” at https://www.shakealert.org/education-outreach/event-review-
files/.
91 The best-case scenarios occur when there are enough seismic stations that detect the P-waves from an earthquake and
can rapidly and accurately estimate the earthquake characteristics. In other scenarios, where fewer seismic stations
detect an event, there may be delays in estimating the earthquake characteristics until the P-waves reach other seismic
stations that are further away. USGS, ShakeAlert Plan, 2018, p. 22; and USGS, Expected Warning Times, 2021, p. 3.
92 Correspondence between CRS and the USGS, January 12, 2022; and ShakeAlert, “Post ShakeAlert Message
Summaries,” at https://www.shakealert.org/education-outreach/event-review-files/.
93 Correspondence between CRS and the USGS, January 12, 2022.
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problems with the software or interaction with the IPAWS gateway.94 The USGS and ShakeAlert
partners are working with FEMA and the FCC to improve the delivery speed of EEWs.95
Experts have generally found that each alerting system (e.g., alerts via television, radio, cell
phones, or machine-to-machine communication) has benefits and challenges.96 EEW apps, for
example, deliver EEW alerts faster than other communication pathways; these apps typically
deliver EEWs to cell phones within a few seconds of receiving a ShakeAlert message.97 A
downside of these EEW apps is that three of the four require users to download the app to their
cell phones (the Google app is built in and does not require owners of Android-based devices to
download an app). If users do not download the app, they cannot receive the EEW. Conversely,
WEA alerts sent from IPAWS to cell phones reach all operational cell phones in the targeted area;
people do not need to opt in or download an app to receive the alert. Further, Wi-Fi or cellular
networks must be operational for people to receive EEWs on their cell phones. If an earthquake
damages or destroys Wi-Fi or cellular networks, people may not be able to get EEWs on their cell
phones. Experts generally assert that multiple communication pathways should be used in case
one pathway is damaged or destroyed.98
LtOs that provide EEWs through institutional communication pathways have found EEW cell
phone apps are the fastest way to warn personnel using electronic devices.99 Mass notification
systems at institutions that use emails, text messages, or reverse 911 for EEWs may not deliver
the warning in time for people to take protective action. Communication pathways such as public
address systems or sirens in buildings are generally fast enough (i.e., the EEW is delivered within
a few seconds) if the systems are connected to Wi-Fi or cellular networks. So far, testing and
development by the USGS, ShakeAlert partners, and some LtOs show that EEW communication
via television, radio, computer, or social media is too slow to be effective. Work is ongoing to
speed up delivery via these other communication pathways.100
Public Reaction to Earthquake Early Warnings
EEWs may reduce risks only if the public receives the warnings, believes the warnings, and takes
immediate protective actions. Past and ongoing surveys study how much of the public knows
about ShakeAlert and how much of the public favors having an EEW system. One 2016 poll in
California found that 88% of the sampled population supported building a statewide EEW system
in California and 75% were willing to pay an additional tax to fund it.101 A survey conducted in
February 2021 indicated that about 25% of the population of California and less than 12% of the
population in Washington and Oregon knew about ShakeAlert.102 The number of cell phone app

94 Ibid.
95 USGS, ShakeAlert Plan, 2018; USGS, Expected Warning Times, 2021, p.3 and FEMA National Advisory Council,
Modernizing the Nation’s Public Alert and Warning System, February 15, 2019, at https://www.hsdl.org/?view&did=
826793.
96 FEMA National Advisory Council, Modernizing the Nation’s Public Alert and Warning System, February 15, 2019,
at https://www.hsdl.org/?view&did=826793, p. 7.
97 USGS, ShakeAlert Plan, 2018; and USGS, Expected Warning Times, 2021, p. 3.
98 FEMA National Advisory Council, Modernizing the Nation’s Public Alert and Warning System, February 15, 2019,
at https://www.hsdl.org/?view&did=826793, p. 7.
99 USGS, ShakeAlert Plan, 2018.
100 USGS, ShakeAlert Plan, 2018; and correspondence between CRS and the USGS, January 12, 2022.
101 Allen and Melgar, “EEW Advances,” 2019, p. 364.
102 Correspondence between CRS and the USGS, January 12, 2022.
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downloads, excluding the Android-based app that does not require a download, is less than 2
million. This total may be lower than expected given that the Android-based app is working on
about 15.6 million Android-based devices on the West Coast, and Android-based devices make up
only about half of the cell phones used on the West Coast.103 Given that most surveyed
Californians in 2016 favored an EEW system, the percentage of people who know about
ShakeAlert and have downloaded a ShakeAlert app may be lower than expected.
In addition to studying public knowledge and interest in receiving EEWs from ShakeAlert, the
USGS and ShakeAlert partners seek to study how people react to EEWs and whether they find
the EEWs valuable. According to previous work in other countries and ongoing ShakeAlert
surveys, individuals do not always immediately DCHO. This may occur because individuals
pause, wait for confirmation of the event or for other people to react, try to help others first, and
for other reasons.104 The 2021 ShakeAlert survey preliminary results regarding the public’s
reaction are consistent with the public reaction to EEW systems in other countries, such as Japan
and New Zealand.105 Most respondents (about 70%) to the ShakeAlert survey who have received
a warning from ShakeAlert were tolerant of potential flaws in the system, were optimistic about
reducing their risk if they received a timely EEW, and saw value in ShakeAlert.106 Past surveys
and current work suggest the public supports an EEW system and the public wants to receive an
EEW if they are in harm’s way.
ShakeAlert Administration
Responsibility and Governance
The USGS leads the ShakeAlert cooperative project. State, academic, and nonprofit organization
partners (Table 2) cooperate and coordinate with the USGS on ShakeAlert activities. The USGS
considers ShakeAlert activities to be part of ANSS, which is overseen by the USGS EHP.107 The
USGS and ShakeAlert partners coordinate with FEMA and NSF on components of the system
and to fulfill related NEHRP responsibilities.108 The USGS and ShakeAlert partners also
coordinate with the National Oceanic and Atmospheric Administration (NOAA) and NASA,
because these agencies support research and development that contributes to advancing EEW
capabilities.109

103 Correspondence between CRS and the USGS, January 12, 2022 and Statista, “Subscriber share held by smartphone
operating systems in the United States from 2012 to 2022,” at https://www.statista.com/statistics/266572/market-share-
held-by-smartphone-platforms-in-the-united-states/. According to the website, Apple iOS-based cell phones account for
about half of the cell phones used in the United States.
104 McBride, “Protective Actions,” 2022.
105 Julia S. Becker et al., “Earthquake Early Warning in Aotearoa New Zealand: A Survey of Public Perspectives to
Guide Warning System Development,” Humanities and Social Sciences Communications, vol. 7, no. 138 (2020), at
https://doi.org/10.1057/s41599-020-00613-9; and Kazuya Nakayachi et al., “Residents’ Reaction to Earthquake Early
Warnings in Japan,” Risk Analysis, vol. 39, no. 8 (2019), pp. 1723-1740, at https://doi.org/10.1111/risa.13306.
106 Correspondence between CRS and the USGS, January 12, 2022.
107 USGS, ShakeAlert Plan, 2018; and correspondence between CRS and the USGS, January 12, 2022. For more
information about ANSS, see footnote 51.
108 See CRS Report R43141, The National Earthquake Hazards Reduction Program (NEHRP): Issues in Brief, by
Linda R. Rowan.
109 NOAA issues tsunami warnings, conducts tsunami research, and conducts geodetic surveys, and these programs
help advance EEW capabilities. NOAA’s National Weather Service Tsunami Warning Centers (see NOAA/NWS,
“U.S. Tsunami Warning System,” at https://www.tsunami.gov/) coordinate with ShakeAlert and other EEW
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The State of California considers ShakeAlert to be its statewide EEW system, led by the Cal OES
in collaboration with the USGS and other ShakeAlert partners. The State of California authorized
Cal OES in collaboration with the USGS, California Institute of Technology, University of
California, California Geological Survey, Alfred E. Alquist Seismic Safety Commission, and
other stakeholders to develop a comprehensive statewide EEW system through a public-private
partnership in 2013. The partnership was not authorized to receive appropriations from the
California General Fund but sought funding for the development of the statewide system from
other sources.110 The state enacted legislation in 2016 that established the California Safety Fund
in the state treasury and allowed appropriations from the General Fund for seismic safety and
earthquake-related programs, including the statewide EEW system. In addition, the 2016
legislation established the California Earthquake Early Warning Program within Cal OES and the
California Earthquake Early Warning Advisory Board to advise the director of Cal OES.111
The Oregon Military Department, Office of Emergency Management, coordinates a statewide
public awareness and participation campaign of ShakeAlert in Oregon with the USGS,
ShakeAlert partners, and ShakeAlert LtOs.112 In Washington, the Washington Military
Department, Emergency Management Division, coordinates a statewide public awareness and
participation campaign of ShakeAlert with the USGS, ShakeAlert partners, and ShakeAlert
LtOs.113
The USGS is coordinating with Canada’s Natural Resources Canada to extend components of
ShakeAlert into western Canada and to coordinate cross-border alerts. In addition, the USGS

development to advance their earthquake detection and tsunami warning decisionmaking when an earthquake triggers a
potentially damaging tsunami. (See Tsunami Science and Technology Advisory Panel, Report and Recommendations
Concerning Tsunami Science and Technology Issues for the United States, NOAA, December 8, 2021, at
https://sab.noaa.gov/wp-content/uploads/2022/01/TSTAP-Report_Oct2021_Final_withCoverandLetter.pdf.) NOAA’s
National Center for Tsunami Research (see NOAA, “National Center for Tsunami Research,” at
https://nctr.pmel.noaa.gov/index.html) focuses on understanding tsunamis. Because many tsunamis are initiated by
earthquakes, some of NOAA’s research focuses on understanding earthquakes, earthquake hazards, and earthquake
risks. NOAA conducts earthquake research in marine environments (see NOAA, Pacific Marine Environmental
Library, “Marine Ecosystem Research,” at https://www.pmel.noaa.gov/pmel-theme/marine-ecosystem-research), and
NOAA coordinates with the USGS, other federal agencies, and states and local entities for some marine research
activities. NOAA’s National Geodetic Survey (see NOAA, “National Geodetic Survey,” at https://geodesy.noaa.gov/)
provides geodetic data, technology, and development that may improve EEW capabilities.
The National Aeronautics and Space Administration’s (NASA’s) Earth Sciences Division supports earthquake research
and development that contribute to EEW capabilities, primarily based on Earth-observing satellite systems (see NASA,
“Supporting Earthquake Response and Recovery,” at https://appliedsciences.nasa.gov/what-we-do/disasters/
earthquakes). NASA’s Space Geodesy Program (see NASA, “SGP: Space Geodesy Program,” at https://space-
geodesy.nasa.gov/about/projOverview.html) operates, maintains, and enhances the Space Geodesy Network and the
Global GNSS Network for the definition of the International Terrestrial Reference Frame, measurement of the Earth
orientation parameters, and satellite precision orbit determination. The program contributes to the research and
development of the geodetic component of ShakeAlert. See also NRC, Precise Geodetic Infrastructure, 2010, pp. 48-
50.
110 Earthquake Early Warning System, Senate Bill No. 135 (SB-135, Chapter 342, Statutes of 2013), California
Government Code Section 8587.8, at https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=
201320140SB135
111 Earthquake Safety: Statewide Earthquake Early Warning Program and System, Senate Bill No. 438 (Chapter 803,
Statutes of 2016), California Government Code Section 8587.8, 8587.11, and 8587.12, at
https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=201520160SB438
112 Oregon Military Department, Office of Emergency Management, “ShakeAlert in Oregon,” at
https://www.oregon.gov/oem/hazardsprep/pages/orshakealert.aspx.
113 Washington Military Department, Emergency Management, “Alert and Warning Notifications, ShakeAlert
Earthquake Early Warning”, at https://mil.wa.gov/alerts.
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aims to collaborate with Mexico’s National Center for Prevention of Disasters and the Ensenada
Center for Scientific Research and Higher Education in Baja California to coordinate on alerts
that may impact Southern California and Baja California, Mexico.
Funding Trends and Estimated Future Costs for ShakeAlert
Congress appropriated funds totaling $162 million between FY2006 and FY2022 to the USGS for
EEW capabilities. In addition, the USGS has cooperative agreements and distributes some of its
appropriated funds to ShakeAlert partners (see Table 2) for research and development, operations
and maintenance, and education and outreach components of ShakeAlert. Nonfederal sources of
funding, mostly from California state and local agencies, contributed another $84 million for
ShakeAlert between 2012 and 2021.
USGS ShakeAlert Funding
Table 5 shows enacted appropriations for EEW within the USGS EHP from FY2006 to
FY2022.114 Congress provided total appropriations of $7.5 million for EEW research,
development, testing, and demonstration from FY2006 to FY2014. In addition, Congress
provided the USGS with appropriations for operations, maintenance, construction, and repair of
critical USGS facilities in the American Recovery and Reinvestment Act (ARRA; P.L. 111-5),
and EHP spent $4.4 million of ARRA funds to build EEW-related systems from 2009 to 2011. In
FY2015, Congress appropriated $5 million for capital costs to begin to transition the EEW
demonstration prototype into an EEW operational capability. In report language accompanying
the FY2022 Consolidated Appropriations Act (P.L. 117-103), Congress recommended $28.6
million for ShakeAlert and an additional $1.0 million in congressionally directed spending for the
USGS and the State of Alaska to develop a plan to implement ShakeAlert in Alaska.115
Table 5. USGS Enacted Appropriations for EEW Activities and ShakeAlert
(amounts in millions of dollars, not adjusted for inflation)
Fiscal Year(s)
Base Funding
Capital Funding
2006-2014
7.5
4.4a
2015
1.5
5.0
2016
8.2
—
2017
10.2
—
2018
12.9
10.0
2019
16.1
5.0
2020
19.0
6.7
2021
25.7
—
2022
29.6b

Total
130.7
31.1
Sources: CRS, with data from USGS, ShakeAlert Plan, 2018 and the USGS, January 12, 2022.

114 USGS, ShakeAlert Plan, 2018.
115 “Joint Explanatory Statement, Division G – Department of the Interior, Environment, and Related Agencies
Appropriations Act, 2022,” p. H2483 - H2484, accompanying P.L. 117-103, at https://www.congress.gov/117/crec/
2022/03/09/168/42/CREC-2022-03-09-bk4.pdf.
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Notes: Congress appropriated funds to the USGS Earthquake Hazards Program for EEW capabilities and/or
ShakeAlert through regular appropriations, except where noted. Base funding covers research and development
and operations and maintenance for EEW activities and ShakeAlert. Capital funding covers the costs of new
equipment and new infrastructure and the costs for installing new stations or upgrading existing stations.
a. Congress appropriated $140 mil ion to the USGS for operations, maintenance, construction, and repair of
facilities and systems in the American Recovery and Reinvestment Act (P.L. 111-5), and the USGS spent
$4.4 mil ion of that total on new equipment and infrastructure for seismic networks that contribute to EEW
capabilities between 2009 and 2011.
b. This base funding includes $1.0 mil ion in congressionally directed spending for the USGS and the State of
Alaska to develop a plan to implement ShakeAlert in Alaska.
Other ShakeAlert Funding
No available estimates show the amount of enacted appropriations that federal agencies other
than the USGS spent on earthquake-related activities that directly or indirectly support EEW.
NSF, through research grants and cooperative agreements, supports research facilitating the
development of EEW capabilities and ShakeAlert components; however, these grants and
agreements also serve other purposes, and it is difficult to estimate what fraction of these funds
supported research that advanced EEW capabilities and ShakeAlert.116 In addition, FEMA and the
FCC are working with the USGS and ShakeAlert partners to improve communication pathways
for EEWs.
From 2012 to 2021, ShakeAlert also received other funds (i.e., funds not directly from the federal
government) totaling $84 million from states, cities, and a foundation (Table 6). These funds
supported the development of ShakeAlert system components, education and outreach, and other
activities. The largest contributor is Cal OES, which has provided $58.6 million for ShakeAlert.
Cal OES funds (1) the installation and upgrading of seismic and geodetic stations in California,
(2) improvements in and integration of telemetry for ShakeAlert raw data in the state, (3) a
comprehensive public awareness and participation campaign, (4) research and development of
various communication pathways (e.g., radio and television) for rapid EEW, and (5)
administration and management of the Earthquake Early Warning Program in California. Cal
OES estimates supporting these aspects of ShakeAlert in California may cost $17.3 million per
year.117 In addition to Cal OES, the Los Angeles/Long Beach Urban Area Security Initiative
provided $5.6 million, mostly for new seismic stations, from funds granted to the initiative by
FEMA.118
Oregon spent $8.5 million from 2015 to 2020 for ShakeAlert components. The State of Oregon
appropriated funds for 15 new seismic stations, the Oregon Department of Geology and Mineral
Industries funded 27 new stations, and the Eugene Water and Electric Board purchased equipment
for two stations.119

116 Although NSF is not officially a ShakeAlert partner, it contributes funding that supports research and infrastructure
that advances aspects of ShakeAlert. It does so through research grants and cooperative agreements to universities,
IRIS, SCEC, and UNAVCO. The USGS expects NSF to continue supporting operations and maintenance for some
networks. USGS, ShakeAlert Plan, 2018.
117 Cal OES, California Earthquake Early Warning Business Plan Update, 2021, p. 12, at https://www.caloes.ca.gov/
EarthquakeTsunamiVolcanoProgramsSite/Documents/CEEWS%20Business%20Plan%20Update%20Final.pdf.
118 USGS, ShakeAlert Plan, 2018, p. 41.
119 USGS, ShakeAlert Plan, 2018.
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Table 6. Nonfederal Funding for the ShakeAlert System
(amounts in millions of dollars, not adjusted for inflation)
Time Frame
Source
Amount
2012-2015
Gordon and Betty Moore
6.5
Foundation
2014-2016
LA/LB UASI
5.6
2016-2018
Gordon and Betty Moore
3.6
Foundation
2016-2021
Cal OES
58.6
2015-2020
Oregon
8.5
2019
Washington
1.2
2012-2021
All Sources
84.0
Sources: CRS, with data from USGS, ShakeAlert Plan, 2018; the USGS, January 12, 2022; and Cal OES, California
Earthquake Early Warning Business Plan Update, 2021, at https://www.caloes.ca.gov/
EarthquakeTsunamiVolcanoProgramsSite/Documents/CEEWS%20Business%20Plan%20Update%20Final.pdf.
Notes: Cal OES = California Governor’s Office of Emergency Services; LA/LB UASI = Los Angeles/Long Beach
Urban Area Security Initiative, which provided funds from the Federal Emergency Management Agency.
2018 Estimate of Costs to Complete ShakeAlert
In 2018, the USGS estimated capital costs to complete ShakeAlert (excluding telemetry) in
California, Oregon, and Washington would be $39.3 million (Table 7). This estimate included
building or upgrading 560 seismic stations for a total seismic network of 1,675 stations;
upgrading 475 geodetic stations; and building or upgrading other network infrastructure.120 The
typical cost to install a new seismic station is $52,600-$64,600, and the typical cost to upgrade a
geodetic station is $27,300-$54,700.121 The USGS-estimated annual operations and maintenance
budget for ShakeAlert was $28.6 million, without the cost for operations and maintenance of
telemetry.122 In 2018, the USGS estimated the additional cost to build out a telemetry system for
ShakeAlert would be $20.5 million and the annual cost for operations and maintenance of the
newly built-out telemetry system would be $9.8 million.123 ShakeAlert partners may cover some
of the costs for telemetry, and costs may have changed since 2018. The USGS and ShakeAlert
partners have not yet received the capital funding needed to complete ShakeAlert.

120 Since 2018, 194 new/upgraded seismic stations have been installed and 299 geodetic stations have been upgraded
(the costs of these upgrades are shared with other ShakeAlert partners), so the current capital costs are less than $39.4
million. Correspondence between CRS and the USGS, January 12, 2022.
121 USGS, ShakeAlert Plan, 2018, pp. 30-31.
122 Ibid.
123 An update to the estimated costs for telemetry was not available as of January 2022. The estimated costs for
operations and maintenance may cover any additional upgrades or repairs for the completed ShakeAlert telemetry
system going forward.
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Table 7. USGS 2018 Estimate of ShakeAlert Costs
(amounts in millions of 2018 dollars)
Annual Operations and
Component
One-Time Capital Costs
Maintenance Costs
Seismic Stations
31.2a
17.1
Geodetic Stations
6.2b
3.5
USGS ShakeAlert Office
1.9
3.0
Research and Development
—
3.2
Communication, Education, and
Outreach
—
1.8
Telemetry
20.5c
9.8d
Total
59.8
38.4
Source: CRS, with data from USGS, ShakeAlert Plan, 2018.
Notes: Figures do not reflect investments made since 2018. Some of the estimated costs listed in this table may
be covered by ShakeAlert partners and other federal agencies, such as NSF and FEMA. For example, the USGS
assumes NSF wil continue to fund the operations and maintenance of the Network of the Americas under a
cooperative agreement with UNAVCO and that FEMA hazard mitigation grants may cover the costs of new or
upgraded seismic or geodetic stations. See USGS, ShakeAlert Plan, 2018, pp. 30-32.
a. CRS calculated that the 194 new seismic stations installed since 2018 at an estimated $52,600 per station
may reduce this estimated cost by $10.2 mil ion. Furthermore, this estimated cost may change, because only
366 new stations are needed as of April 2022 and because ShakeAlert partners or FEMA may cover the
costs of some new stations.
b. The remaining one-time capital cost for upgrades may be different than the 2018 estimate shown because
299 geodetic stations have been upgraded (some of the costs of these upgrades were covered by other
ShakeAlert partners). Only 176 geodetic stations needed upgrades as of April 2022.
c. The one-time capital costs to complete the telemetry needed for the ShakeAlert system on the West Coast
is an estimate of the USGS costs. The cost may change if ShakeAlert partners, FEMA, and/or NSF cover
some of the costs of telemetry upgrades. See USGS ShakeAlert Plan, 2018, p. 42, for ful details of this cost
estimate.
d. The annual operations and maintenance cost is for the new telemetry only (i.e., the $20.5 mil ion of new
telemetry costs estimated in the previous column).
Comparison of ShakeAlert with Other Earthquake
Early Warning Systems
Comparing ShakeAlert with other EEW systems may help stakeholders improve the ShakeAlert
system, consider alternative components or technology, and coordinate and cooperate on
advancing EEW throughout the world (Figure 11). Two types of EEW system are used today.
One type uses an earthquake-sensing network consisting of seismic and/or geodetic stations
spatially distributed around active faults for optimal earthquake detection. These networks can
generally rapidly and accurately detect P-waves and provide effective EEWs. The second type
uses a fixed or crowd-sourced cell phone network to detect accelerations caused by
earthquakes.124 Cell phones have miniature accelerometers and Global Navigation Satellite

124 Most cell phone-based networks cannot detect the first arriving P-waves, but rely on detecting the stronger and later
arriving S-waves. This means that the EEW is delayed and that the cell phones used to detect the S-waves provide no
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System (GNSS) receivers that are not as accurate or sensitive as seismic or geodetic instruments,
respectively, but cell phones can function as approximate earthquake detectors. In addition, cell
phones provide a communication pathway and may send EEWs to other cell phones using apps
via Wi-Fi or cellular networks.
The USGS and ShakeAlert partners may consider how EEW systems in other countries are
working and how countries might share earthquake understanding, risk reduction, and any
techniques to better detect and mitigate earthquake hazards. China, India, Italy, Japan, Mexico,
Romania, South Korea, Taiwan, and Turkey have regional to nationwide public-alerting EEW
systems that use standard earthquake-sensing networks. Austria, Chile, Costa Rica, El Salvador,
Greece, Iceland, Italy, Israel, New Zealand, Nicaragua, Slovenia, Spain, and Switzerland are
testing similar EEW systems.125 Canada aims to begin testing ShakeAlert as soon as components
are established and operating.126
A comparison of ShakeAlert with standard earthquake-sensing networks used in other countries
may help reveal the optimal location, deployment, station technology, telemetry technology, and
data analysis techniques for earthquake detection and the most effective communication pathways
for EEWs. Mexico City established the first public EEW system in 1991.127 Today, Mexico’s
earthquake-sensing network uses fewer than 100 seismic stations to cover an area comparable to
the area of California, Oregon, and Washington combined. Mexico’s system provides EEWs to
Mexico City and a few other cities primarily via tens of thousands of radios and thousands of
sirens installed throughout urban areas. In contrast, Japan’s EEW system, established in 2006,
uses more than 4,000 seismic stations and more than 1,000 geodetic stations on land and on the
seafloor, covering an area comparable to the area of California. Japan provides EEWs nationwide
through multiple communication pathways including television, radio, and cell phones. In
general, ShakeAlert is larger and more sophisticated than Mexico’s system and smaller and less
sophisticated than Japan’s system.

warning to their owners in advance of intense ground shaking. Benjamin A. Brooks et al., “Robust earthquake early
warning at a fraction of the cost: ASTUTI Costa Rica,” AGU Advances, vol. 2 (May 2021), e2021AV000407, pp. 1-17,
https://doi. org/10.1029/2021AV000407.
125 Gemma Cremen and Carmine Galasso, “Earthquake Early Warning: Recent Advances and Perspectives,” Earth
Science Reviews, vol. 205 (June 2020), pp. 1-15, at https://doi.org/10.1016/j.earscirev.2020.103184.
126 Canada is developing an EEW system at the federal level through Natural Resources Canada. Canada faces
earthquake risks on the west coast because of the Cascadia Subduction Zone (CSZ), which also affects the United
States. Canada is working with ShakeAlert to extend the ShakeAlert system into Canada and to cooperate on
earthquake detection and warning across the CSZ. For the latest information about Canada’s EEW system, see
Meghomita Das, Engaging Communities with Canada’s Earthquake Early Warning System, Temblor, December 16,
2021, at https://doi.org/10.32858/temblor.224.
127 SASMEX, 2018.
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Figure 11. Timeline of Public EEW by Country or Region and
Population Size Alerted

Source: Sara K. McBride et al., “Evidence-Based Guidelines for Protective Actions and Earthquake Early
Warning Systems,” Geophysics, vol. 87, no. 1 (January-February 2022), WA77-WA102, at https://doi.org/10.1190/
GEO2021-0222.1.
Notes: Limited alerts have been sent in Costa Rica and El Salvador but are not shown on this graphic.
Issues for Congress
ShakeAlert has been operating in California since October 2019 and in Oregon and Washington
since 2021. Given that the system is relatively new, additional information to assess ShakeAlert’s
performance and effectiveness may be useful to Congress. An assessment could examine
information on improvements in the earthquake-sensing network and data analysis, the
communication of EEWs, and funding. Seismic and geodetic networks that are now components
of ShakeAlert’s earthquake-sensing network were established for other purposes; they have been
used for ShakeAlert while continuing to serve these other purposes. An evaluation of whether
these components are effective for EEW and how these components might be used effectively for
multiple purposes, perhaps with further coordination among the component operators, also may
be useful for Congress. For example, the Network of the Americas, operated by UNAVCO Inc.,
supports basic research; the network’s operations and maintenance are funded through a
cooperative agreement with NSF.128 In addition, NOAA’s National Geodetic Survey uses
hundreds of the geodetic stations in the Network of the Americas to help define the National

128 UNAVCO, “Network of the Americas,” at https://www.unavco.org/projects/major-projects/nota/nota.html.
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Spatial Reference System.129 Thus, the Network of the Americas supports research, EEW, and
surveying with funding from different federal agencies.
As part of an evaluation, Congress could direct the USGS to analyze ShakeAlert’s performance
and provide recommendations for improving, expanding, or contracting the current system. Any
evaluation may consider the USGS and ShakeAlert partners’ aim to increase the size of the
earthquake-sensing network on the West Coast, as discussed in the 2018 USGS ShakeAlert
Plan.130 According to the USGS, the planned size would ensure rapid and accurate earthquake
detection for effective EEW on the West Coast. The USGS analysis of the performance of
ShakeAlert from October 2019 to December 2021 shows that some earthquakes were missed or
miscalculated because of inadequate station coverage. The USGS indicates that more seismic
stations plus the integration of the geodetic data into the data processing may improve the
performance of ShakeAlert on the West Coast. Further, the USGS and ShakeAlert partners aim to
improve the data algorithms and data processing in order to prepare more timely and accurate
alert messages.
Congress may consider expanding ShakeAlert into other states or specific regions (i.e., some
parts of some states). For example, the 2018 USGS ShakeAlert Plan aims to expand ShakeAlert
into Alaska, Hawaii, and Nevada. Congress directed the USGS and the State of Alaska to develop
an implementation plan for ShakeAlert in Alaska in FY2022 appropriations.131
Currently, most of FEMA’s communication pathways are not fast enough for effective EEWs.
Congress may consider requesting FEMA to evaluate its communication pathways and make
suggestions about how FEMA may improve its technology and techniques to meet the challenge
of rapid, targeted mass notification for earthquakes.132 In addition, FEMA may be able to evaluate
whether these improvements may be applied for rapid warning about other hazards, such as
further developing communication protocols for rapid and targeted mass notification for
tornadoes.133 Another potential area for oversight is related to how federal communication
pathways operate in coordination or in parallel with nonfederal communication pathways to
provide the most effective disaster warnings to states and civilian populations in endangered
areas. In particular, the continued growth of cell phone EEW apps for public warnings may create
issues regarding security, privacy, accuracy, reliability, accessibility, and authority. Congress may
consider how agreements between federal agencies, such as the USGS’s LtOs, and nonfederal
communication providers address these issues. These oversight and policy considerations may
lead to changes in NEHRP or the Stafford Act, which in turn may impact funding and funding
priorities.

129 NOAA, “National Geodetic Survey,” at https://geodesy.noaa.gov/INFO/WhatWeDo.shtml.
130 USGS, ShakeAlert Plan, 2018.
131 Explanatory Statement, Division G – Department of the Interior, Environment, and Related Agencies
Appropriations Act, FY2022 to accompany H.Rept. 117-83 for P.L. 117-103.
132 For example, see FEMA National Advisory Council, Modernizing the Nation’s Public Alert and Warning System,
February 15, 2019, at https://www.hsdl.org/?view&did=826793 and the recent contract awarded to AT&T to
modernize FEMA’s IPAWS, AT&T Communications, “FEMA Awards AT&T 4 EIS Contracts Valued at $167M/5-
Years to Modernize Its Communications Capabilities,” press release, February 15, 2022, at
https://www.prnewswire.com/news-releases/fema-awards-att-4-eis-contracts-valued-at-167m5-years-to-modernize-its-
communications-capabilities-301482531.html.
133 See Cliff Mass, “A Critical Gap in Tornado Warning Technology: Lessons of the Recent Tornado Outbreak,” Cliff
Mass Weather Blog, December 12, 2021, at https://cliffmass.blogspot.com/2021/12/a-critical-gap-in-tornado-
warning.html.
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The USGS notes that ShakeAlert has not yet received all of the funding estimated to complete the
system or to support annual operations and maintenance in the future.134 If Congress chooses to
continue to provide funding for ShakeAlert, there are a range of options to consider, such as
annual appropriations or through shared costs similar to those that support other observing
networks in the United States that are a mix of federal- and state-funded initiatives (e.g., NOAA
Continuously Operating Reference Stations and USGS Streamgaging Network).135 Other funding
options for consideration may include funding aspects of ShakeAlert through established NSF or
FEMA federal grants, contracts, or cooperative agreements or through new NSF or FEMA federal
grants, contracts, or cooperative agreements. In addition, Congress may consider policy options
that would enable NOAA or NASA to contribute funds for ShakeAlert as well as research and
development for EEW capabilities.
Congress may consider policy options that would improve insight into how federal funds are used
to support ShakeAlert and that support other related activities. The USGS, NSF, NIST, and FEMA
receive appropriations for earthquake hazards risk reduction through NEHRP or for research and
development related to hazard mitigation objectives; however, except for those identified by the
USGS for EEW, how other agencies used appropriated funds for ShakeAlert is difficult to track,
because those funds were not specifically appropriated for ShakeAlert.

134 USGS, ShakeAlert Plan, 2018, p. 30 – 32.
135 NOAA, “National Geodetic Survey, The NOAA CORS Network (NCN),” at https://geodesy.noaa.gov/CORS/ and
USGS, “USGS Streamgaging Network,” at https://www.usgs.gov/mission-areas/water-resources/science/usgs-
streamgaging-network.
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Appendix. Earthquake Magnitude, Shaking
Intensity Scale, and Hazards
Earthquake magnitude is determined for every observed earthquake and often estimated for older
events that happened before earthquake-sensing instruments existed in order to compare these
events to current events and to estimate the possible recurrence rate of earthquakes on a fault.136
Magnitude is rapidly estimated for earthquake early warning (EEW), and the estimated
magnitude may change as more data are collected or because the earthquake may continue to
“grow” with time (i.e., the movement along a fault may continue over seconds to minutes leading
to a larger area of movement and a larger magnitude event). A changing magnitude estimate can
complicate EEW and can make EEW less effective in reducing risks because the warning must be
rapid, leaving little to no time to reassess an estimated magnitude.
For the public, specifying the magnitude provides a way to understand the “size” of the event
using a familiar parameter and to compare the event to previous newsworthy events. For
earthquake scientists, magnitude provides a measurement of the length and area of the fault that
slipped and the strength of the rock involved in the rupture. These parameters improve an
understanding of what causes an earthquake and whether the fault is more or less likely to have
an earthquake over a specified future period. Magnitude can be calculated in different ways, and
this report cites moment magnitude (M). Moment magnitude is based on the strength of the rock,
the fault surface area that ruptures, and the amount of slip along the fault. This magnitude
calculation may be the closest to the public’s perspective that the earthquake magnitude
represents the “size” of the earthquake, given that a longer and more extensive fault may produce
a larger magnitude event because there is more length and area that can slip, producing a larger
moment magnitude event.
Magnitude can be converted into the energy released by the earthquake. The energy released
increases by about 32 times for each single step in magnitude (Figure A-1), so an M9.0 event is
much more energetic than an M8.0 event. An M9.0 event may cause surface shaking that is much
more intense, covers a larger area, and is of a longer duration than surface shaking from an M8.0
event. The public may not fully understand that each magnitude step means a much more
energetic earthquake that may cause much more intense ground shaking. However, for EEW and
other earthquake notifications for the public, it is important to quickly estimate the magnitude and
determine where and how much intense shaking the earthquake may cause. In the case of the
2011 M9.1 Tohoku earthquake, Japan’s EEW system underestimated the magnitude as an M8.0,
leading to no warning or less warning (i.e., less intense shaking over a smaller area was expected
and the larger area that was impacted by the tsunami were not anticipated) for a much more
energetic event.137

136 U.S. Geological Survey (USGS), “Magnitude Types,” at https://www.usgs.gov/programs/earthquake-hazards/
magnitude-types.
137 For more information about the 2011 M9.1 Tohoku earthquake and the magnitude underestimate, see Richard M.
Allen and Diego Melgar, “Earthquake Early Warning: Advances, Scientific Challenges and Societal Needs,” Annual
Review of Earth and Planetary Sciences, vol. 47 (2019), pp 361-388 (see p. 374), at https://doi.org/10.1146/annurev-
earth-053018-060457 (hereinafter, Allen and Melgar, “EEW Advances,” 2019) and National Research Council, Precise
Geodetic Infrastructure: National Requirements for a Shared Resource (Washington, DC: National Academies Press,
2010), at https://doi.org/10.17226/12954.
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Figure A-1. Earthquake Magnitude and Energy Released

Source: The figure is from ShakeAlert, “ShakeAlert Graphics Library,” at https://www.shakealert.org/
messaging_toolkit/graphics-library/.
Note: For more details about magnitude and the amount of energy released for a given magnitude, see USGS
“Earthquake Magnitude, Energy Release and Shaking Intensity,” at https://www.usgs.gov/programs/earthquake-
hazards/earthquake-magnitude-energy-release-and-shaking-intensity.
An earthquake shaking intensity scale, called the Modified Mercalli Intensity (MMI) scale, is
used for EEW and in post-earthquake assessments to compare and describe earthquake intensity
on the surface with one consistent, comparable parameter.138 The MMI scale depicts the intensity
of the shaking based on how intensely people feel the shaking and the amount of damage the
shaking causes to structures (Table A-1). The scale is empirical and is based on previous
observations. For example, light shaking of MMI intensity IV refers to people indoors feeling the
shaking. For intensities greater than V, the expected experiences refer to the potential impact of
the shaking on structures. For example, violent shaking of MMI IX refers to structures that have
substantial damage.

138 For more details, see USGS, “The Modified Mercalli Intensity Scale,” at https://www.usgs.gov/programs/
earthquake-hazards/modified-mercalli-intensity-scale.
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Table A-1. Modified Mercalli Intensity Scale
Intensity
Shaking
Description

Not felt except by a very few under especial y favorable conditions.
Not felt

Felt only by a few persons at rest, especial y on upper floors of buildings.
Weak

Felt quite noticeably by persons in doors, especial y on upper floors of buildings.
Many people do not recognize it as an earthquake. Standing motor cars may rock
Weak
slightly. Vibrations similar to the passing of a truck. Duration estimated.

Felt indoors by many, outdoors by few during the day. At night, some awakened.
Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy
Light
truck striking building. Standing motor cars rocked noticeably.

Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable
objects overturned. Pendulum clocks may stop.
Moderate

Felt by all, many frightened. Some heavy furniture moved; a few instances of a
fallen plaster. Damage slight.
Strong

Damage negligible in buildings of good design and construction; slight to moderate
Very
in well-build ordinary structures; considerable damage in poorly built or badly
strong
designed structures; some chimneys broken.

Damage slight in special y designed structures; considerable damage in ordinary
substantial buildings with partial col apse. Damage great in poorly built structures.
Severe
Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture

overturned.

Damage considerable in specially designed structures; well-designed frame
structures thrown out of plumb. Damage great in substantial buildings, with partial
Violent
col apse. Buildings shifted off foundations.

Some well-built wooden structures destroyed; most masonry and frame structures
destroyed with foundations. Rails bent.
Extreme

Source: Douglas D. Given et al., Revised Implementation Plan for the ShakeAlert System: An Earthquake Early
Warning System for the West Coast of the United States, USGS, Open-File Report 2018–1155, 2018. Modified by
CRS.
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Earthquake hazards include ground movement, ground displacement, ground shaking, and
liquefaction (Figure A-2).139 The location, depth, type of fault, and magnitude of the earthquake
determine whether any of these hazards may occur at or near the surface, whether the event may
cause damage, and where the event may cause damage. Higher-magnitude earthquakes that
release more energy and earthquakes at shallow depth may cause damaging surface hazards.140 An
earthquake can trigger other natural hazards, such as tsunamis, landslides, fires, floods, or
volcanic eruptions. Earthquake hazards can damage property, such as structural cracks, structural
collapse, fires, explosions, floods, loss of power, loss of water supplies, loss of communication,
and other damage. Earthquake hazards can cause injuries and fatalities. People are injured or
killed mostly by tripping and falling during ground shaking or by being hit or trapped under fallen
objects or shake-damaged structures.141 Subsequent hazards caused by the earthquake, such as
tsunami waves, fires, and floods, may injure or kill more people and damage more structures after
the earthquake.

139 Liquefaction occurs when earthquake-induced ground shaking causes loose, weak, or water-saturated soils or rocky
materials to lose their strength. When liquefaction happens around structures, such as buildings or bridges, these
structures can be damaged or collapse because the foundations of these structures are no longer supported. For more
information about liquefaction, see the USGS, “What is Liquefaction?” at https://www.usgs.gov/faqs/what-liquefaction
140 There is no minimum or maximum earthquake depth used to determine whether ground shaking, ground
displacement/movement, or liquefaction may occur; however, observations of past earthquakes suggest earthquakes at
shallower depths of 0-50 kilometers (0-31 miles) may cause surface damage, depending on their magnitude and other
factors. See the USGS, “What Depth Do Earthquakes Occur?” at https://www.usgs.gov/faqs/what-depth-do-
earthquakes-occur-what-significance-depth.
141 See Occupational Safety and Health Administration “Earthquakes,” at https://www.osha.gov/emergency-
preparedness/guides/earthquakes for more details.
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Figure A-2. Earthquake Hazards

Source: U.S. Government Accountability Office (GAO), EARTHQUAKES Progress Made to Implement Early
Warning System, But Actions Needed to Improve Program Management, GAO-21-129, March 2019 (modified by
CRS).

Author Information

Linda R. Rowan

Analyst in Natural Resources Policy

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Disclaimer
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