Earthquakes: Risk, Detection, Warning, and
Research
Peter Folger
Specialist in Energy and Natural Resources Policy
February 8, 2011
Congressional Research Service
7-5700
www.crs.gov
RL33861
CRS Report for Congress
P
repared for Members and Committees of Congress
Earthquakes: Risk, Detection, Warning, and Research
Summary
The United States faces the possibility of large economic losses from earthquake-damaged
buildings and infrastructure. The Federal Emergency Management Agency has estimated that
earthquakes cost the United States, on average, over $5 billion per year. California, Oregon, and
Washington account for nearly $4.1 billion (77%) of the U.S. total estimated average annualized
loss. California alone accounts for most of the estimated annualized earthquake losses for the
nation.
A single large earthquake, however, can cause far more damage than the average annual estimate.
The 1994 Northridge (CA) earthquake caused as much as $26 billion (in 2005 dollars) in damage
and was one of the costliest natural disasters to strike the United States. One study of the damage
caused by a hypothetical magnitude 7.8 earthquake along the San Andreas Fault in southern
California projected as many as 1,800 fatalities and more than $200 billion in economic losses.
An issue for the 112th Congress is whether existing federally supported programs aimed at
reducing U.S. vulnerability to earthquakes are an adequate response to the earthquake hazard.
Under the National Earthquake Hazards Reduction Program (NEHRP), four federal agencies have
responsibility for long-term earthquake risk reduction: the U.S. Geological Survey (USGS), the
National Science Foundation (NSF), the Federal Emergency Management Agency (FEMA), and
the National Institute of Standards and Technology (NIST). They variously assess U.S.
earthquake hazards, deliver notifications of seismic events, develop measures to reduce
earthquake hazards, and conduct research to help reduce overall U.S. vulnerability to earthquakes.
Congressional oversight of the NEHRP program might revisit how well the four agencies
coordinate their activities to address the earthquake hazard. Better coordination was a concern
that led to changes to the program in legislation enacted in 2004 (P.L. 108-360).
P.L. 108-360 authorized appropriations for NEHRP through FY2009. Total funding enacted from
reauthorization through FY2009 was $613.2 million, approximately 68% of the total amount of
$902.4 million authorized by P.L. 108-360. Congress appropriated $131.2 million for NEHRP in
FY2010, similar to FY2009 funding levels. Also, the American Recovery and Reinvestment Act
(ARRA; P.L. 111-5) provided some additional funding for earthquake activities under NEHRP.
What effect funding at the levels enacted through FY2010 under NEHRP has had on the U.S.
capability to detect earthquakes and minimize losses after an earthquake occurs is difficult to
assess. The effectiveness of the NEHRP program is a perennial issue for Congress: it is inherently
difficult to capture precisely, in terms of dollars saved or fatalities prevented, the effectiveness of
mitigation measures taken before an earthquake occurs. A major earthquake in a populated urban
area within the United States would cause damage, and a question becomes how much damage
would be prevented by mitigation strategies underpinned by the NEHRP program.
Legislation was introduced during the 111th Congress (H.R. 3820) that would have made changes
to the program and would have authorized appropriations totaling $906 million over five years for
NEHRP. Ninety percent of the funding would have been designated for the USGS and NSF, and
the remainder for FEMA and NIST. The bill passed the House but not the Senate. Similar
legislation will likely be introduced in the 112th Congress.
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Contents
Introduction ................................................................................................................................ 1
National Earthquake Hazards Reduction Program (NEHRP) ....................................................... 1
A Shift in Program Emphasis to Hazard Reduction................................................................ 2
NEHRP Legislation in the 111th Congress.............................................................................. 4
Earthquake Hazards and Risk...................................................................................................... 5
United States National Seismic Hazard Map.......................................................................... 5
2008 Update to the National Seismic Hazard Map........................................................... 6
Earthquake Forecast for California .................................................................................. 7
How Many Earthquakes Occur Each Year?...................................................................... 7
Earthquake Fatalities....................................................................................................... 8
Estimating Potential Losses from Earthquakes ...................................................................... 9
A Decrease in Estimated Loss?...................................................................................... 11
The New Madrid Seismic Zone ........................................................................................... 12
Earthquakes in Haiti and Chile—Some Comparisons .......................................................... 13
January 12, 2010, Magnitude 7.0 Earthquake in Haiti .................................................... 13
February 27, 2010, Magnitude 8.8 Earthquake in Chile ................................................. 14
Is There a Similar Risk to the United States? ................................................................. 15
Monitoring................................................................................................................................ 16
Advanced National Seismic System (ANSS) ....................................................................... 16
ANSS Funding.............................................................................................................. 16
Dense Urban Networks ................................................................................................. 17
Backbone Stations......................................................................................................... 17
National Strong-Motion Project (NSMP)....................................................................... 17
Regional Networks........................................................................................................ 17
Global Seismic Network (GSN) .......................................................................................... 18
Detection, Notification, and Warning......................................................................................... 18
National Earthquake Information Center (NEIC)................................................................. 19
ShakeMap........................................................................................................................... 20
Prompt Assessment of Global Earthquakes for Response (PAGER) ..................................... 20
Pre-disaster Planning: HAZUS-MH .................................................................................... 23
Research—Understanding Earthquakes ..................................................................................... 23
U.S. Geological Survey....................................................................................................... 23
National Science Foundation............................................................................................... 24
EarthScope.................................................................................................................... 24
Network for Earthquake Engineering Simulation........................................................... 25
Conclusion................................................................................................................................ 25
Figures
Figure 1. NEHRP Agency Responsibilities and End Users of NEHRP Outcomes ......................... 3
Figure 2. Earthquake Hazard in the United States ........................................................................ 5
Figure 3. Histogram of the Number of U.S. Earthquakes from 2000 to 2009 by
Magnitude (1.0 to 6.9).............................................................................................................. 8
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Figure 4. Example of a ShakeMap............................................................................................. 21
Figure 5. Example of PAGER Output for the January 12, 2010,
Magnitude 7.0 Haiti Earthquake ............................................................................................. 22
Tables
Table 1. Authorized and Enacted Funding for NEHRP................................................................. 4
Table 2. Earthquakes Responsible for Most U.S. Fatalities Since 1970......................................... 8
Table 3. U.S. Metropolitan Areas with Estimated Annualized Earthquake Losses of More
Than $10 Million ................................................................................................................... 10
Contacts
Author Contact Information ...................................................................................................... 26
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Introduction
Close to 75 million people in 39 states face some risk from earthquakes. Earthquake hazards are
greatest in the western United States, particularly in California, but also in Alaska, Washington,
Oregon, and Hawaii. Earthquake hazards are also prominent in the Rocky Mountain region and
the New Madrid Seismic Zone (a portion of the central United States), as well as in portions of
the eastern seaboard, particularly South Carolina. Given the potentially huge costs associated with
a large, damaging earthquake in the United States, an ongoing issue for Congress is whether the
federally supported earthquake programs are appropriate for the earthquake risk.
Under the National Earthquake Hazards Reduction Program (NEHRP), the federal government
supports efforts to assess and monitor earthquake hazards and risk in the United States. Four
federal agencies responsible for long-term earthquake risk reduction coordinate their activities
under NEHRP: the U.S. Geological Survey (USGS), the National Science Foundation (NSF), the
Federal Emergency Management Agency (FEMA), and the National Institute of Standards and
Technology (NIST). Congress last made changes to NEHRP in 2004 (P.L. 108-360), and
authorized appropriations through FY2009 for a total of $902.4 million over five years. A bill
introduced in the 111th Congress, H.R. 3820 (Title I), would have made further changes to the
program and authorized appropriations through FY2014, but it was not enacted.
This report discusses:
• NEHRP—the multi-agency federal program to reduce the nation’s risk from
earthquakes;
• earthquake hazards and risk in the United States;
• federal programs that support earthquake monitoring;
• the U.S. capability to detect earthquakes and issue notifications and warnings;
and
• federally supported research to improve the fundamental scientific understanding
of earthquakes with a goal of reducing U.S. vulnerability.
National Earthquake Hazards Reduction Program
(NEHRP)
In 1977 Congress passed the Earthquake Hazards Reduction Act (P.L. 95-124) establishing
NEHRP as a long-term earthquake risk reduction program for the United States. The program
initially focused on research, led by USGS and NSF, toward understanding and ultimately
predicting earthquakes. Earthquake prediction has proved intractable thus far, and the NEHRP
program shifted its focus to minimizing losses from earthquakes after they occur. FEMA was
created in 1979 and President Carter designated it as the lead agency for NEHRP. In 1980,
Congress passed the Earthquake Hazards Reduction Act (P.L. 96-472), defining FEMA as the lead
agency and authorizing additional funding for earthquake hazard preparedness and mitigation for
FEMA and the National Bureau of Standards (now NIST).
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A Shift in Program Emphasis to Hazard Reduction
NEHRP’s original focus on research to predict earthquakes was changed in 1990, when Congress
enacted P.L. 101-614. Congress decreased the emphasis on earthquake prediction, clarified the
role of FEMA, clarified and expanded the program objectives, and required federal agencies to
adopt seismic safety standards for new and existing federal buildings. In 2004, Congress enacted
P.L. 108-360 and adjusted the program again by shifting primary responsibility for planning and
coordinating NEHRP from FEMA to NIST. P.L. 108-360 also established a new interagency
coordinating committee and a new advisory committee, both focused on earthquake hazards
reduction.
The current program activities are focused on four broad areas:
• developing effective measures to reduce earthquake hazards;
• promoting the adoption of earthquake hazard reduction activities by federal,
state, and local governments, national building standards and model building
code organizations, engineers, architects, building owners, and others who play a
role in planning and constructing buildings, bridges, structures, and critical
infrastructure or “lifelines”;1
• improving the basic understanding of earthquakes and their effects on people and
infrastructure, through interdisciplinary research involving engineering, natural
sciences, and social, economic, and decision sciences; and
• developing and maintaining the Advanced National Seismic System (ANSS), the
George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES),
and the Global Seismic Network (GSN).2
The House Science Committee report in the 108th Congress on H.R. 2608 (P.L. 108-360) noted
that NEHRP has produced a wealth of useful information since 1977, but it also stated that the
program’s potential has been limited by the inability of the NEHRP agencies to coordinate their
efforts.3 The committee asserted that restructuring the program with NIST as the lead agency,
directing funding towards appropriate priorities, and implementing it as a true interagency
program would lead to improvement.
The 2004 law directed the Director of NIST to chair the Interagency Coordinating Committee.
Other members of the committee include the directors of FEMA, USGS, NSF, the Office of
Science and Technology Policy, and the Office of Management and Budget. The Interagency
Coordinating Committee is charged with overseeing the planning, management, and coordination
of the program. Primary responsibilities for the NEHRP agencies break down as follows (see also
Figure 1):
1 Lifelines are essential utility and transportation systems.
2 ANSS is a nationwide network of seismographic stations operated by the USGS. GSN is a global network of stations
coordinated by the Incorporated Research Institutions for Seismology (IRIS, a nonprofit organization). NEES is an
NSF-funded project that consists of 15 experimental facilities and an IT infrastructure with a goal of mitigating
earthquake damage by the use of improved materials, designs, construction techniques, and monitoring tools.
3 U.S. House, Committee on Science, National Earthquake Hazards Reduction Program Reauthorization Act of 2003,
H.Rept. 108-246 (Aug. 14, 2003), p. 13.
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• NIST is the lead NEHRP agency and has primary responsibility for NEHRP
planning and coordination. NIST supports the development of performance-based
seismic engineering tools and works with FEMA and other groups to promote the
commercial application of the tools through building codes, standards, and
construction practices.
• FEMA assists other agencies and private-sector groups to prepare and
disseminate building codes and practices for structures and “lifelines”, and aids
development of performance-based codes for buildings and other structures.
• USGS conducts research and other activities to characterize and assess
earthquake risks, and (1) operates a forum, using the National Earthquake
Information Center (NEIC), for the international exchange of earthquake
information; (2) works with other NEHRP agencies to coordinate activities with
earthquake reduction efforts in other countries; and (3) maintains seismic hazard
maps in support of building codes for structures and lifelines, and other maps
needed for performance-based design approaches.
• NSF supports research to improve safety and performance of buildings,
structures, and lifelines using the large-scale experimental and computational
facilities of NEES and other institutions engaged in research and implementation
of NEHRP.
Figure 1. NEHRP Agency Responsibilities and End Users of NEHRP Outcomes
Source: NEHRP program office at http://www.nehrp.gov/pdf/ppt_sdr.pdf (modified by CRS).
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Table 1 shows the authorized and enacted appropriations for NEHRP from FY2005 through
FY2010. The total enacted amount for FY2005-FY2009 was $613.2 million, or 68% of the
$902.4 million total amount authorized in P.L. 108-360 over the five-year span. President Obama
requested a total of $129.7 million for NEHRP in FY2011, even though authorization of
appropriations for the program under P.L. 108-360 expired at the end of FY2009.
Table 1. Authorized and Enacted Funding for NEHRP
($ millions)
USGS
NSF
FEMA
NIST
Total
FY2005
Authorized
77.0 58.0 21.0 10.0 166.0
Enacted 58.4 53.1 14.7 0.9 127.1
FY2006
Authorized
84.4 59.5 21.6 11.0 176.5
Enacted 54.5
53.8
9.5
0.9
118.7
FY2007
Authorized
85.9 61.2 22.3 12.1 181.5
Enacted 55.4
54.2
7.2
1.7
118.5
FY2008
Authorized
87.4 62.9 23.0 13.3 186.6
Enacted 58.1
53.6
6.1
1.7
119.5
FY2009
Authorized
88.9 64.7 23.6 14.6 191.8
Enacted 61.2
55.0
9.1
4.1
129.4
FY2010 Enacted
62.8
55.3
9.0
4.1
131.2
FY2011 Requested
62.3
54.3
9.0
4.1
129.7
Source: NEHRP program office, at http://www.nehrp.gov/pdf/2010NEHRPAnnualReport.pdf.
Notes: According to the NEHRP program office, ARRA funds are not included. The FY2011 requested budget is
the estimated portion of the President’s budget request that would be al ocated for NEHRP activities. The
FY2010 enacted amounts are estimates.
NEHRP Legislation in the 111th Congress
Title I of H.R. 3820, the Natural Hazards Risk Reduction Act of 2009, introduced in the 111th
Congress, would have made changes to NEHRP and authorized appropriations for the program
through FY2014. The bill was reported by the House Science and Technology Committee on
February 26, 2010, and was passed by the House on March 2, 2010. The Senate did not act on the
bill. The legislation would have retained NIST as the lead NEHRP agency, and authorized total
appropriations of about $906 million over five years. Title II of H.R. 3820 would have made
changes to the National Windstorm Impact Reduction Act (first enacted in 2004 as Title II of P.L.
108-360 and modeled after NEHRP), and Title III would have created an interagency
coordinating committee, chaired by the Director of NIST, to oversee the planning and
coordination of both the earthquake and wind hazards programs. The single interagency
coordinating committee would have replaced the two separate interagency committees overseeing
the current earthquake and wind hazards programs.
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Earthquake Hazards and Risk
Portions of all 50 states and the District of Columbia are vulnerable to earthquake hazards,
although risks vary greatly across the country and within individual states. Seismic hazards are
greatest in the western United States, particularly in California, Washington, Oregon, and Alaska
and Hawaii. Alaska is the most earthquake-prone state, experiencing a magnitude 7 earthquake
almost every year and a magnitude 8 earthquake every 14 years on average. (See box below for a
description of earthquake magnitude.) Because of its low population and infrastructure density,
Alaska has a relatively low risk for large economic losses from an earthquake. In contrast,
California has more citizens and infrastructure at risk than any other state because of the state’s
frequent seismic activity combined with its large population.
United States National Seismic Hazard Map
Figure 2 shows where earthquakes are likely to occur in the United States and how severe the
earthquake magnitude and resulting ground shaking are likely to be. The map in Figure 2 depicts
the potential shaking hazard from future earthquakes. It is based on the frequency at which
earthquakes occur in different areas and how far the strong shaking extends from the source of the
earthquake. In Figure 2, the hazard levels indicate the potential ground motion—expressed as a
percentage of the acceleration due to gravity (g). In a sense, the map shows the likelihood of
where earthquakes could occur, and where the strongest shaking could take place.
Figure 2. Earthquake Hazard in the United States
Source: USGS Fact Sheet 2008-3018 (April 2008), at http://pubs.usgs.gov/fs/2008/3018/pdf/FS08-3018_508.pdf.
Modified by CRS.
Note: The bar in the upper right shows the potential ground motion—expressed as a percentage of the
acceleration due to gravity (g)—with up to a 1 in 50 chance of being exceeded over a 50-year period.
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Figure 2 also shows relatively high earthquake hazard in the Rocky Mountain region, portions of
the eastern seaboard—particularly South Carolina—and a part of the central United States known
as the New Madrid Seismic Zone (see “The New Madrid Seismic Zone” below). Other portions
of the eastern and northeastern United States are also vulnerable to moderate seismic hazard.
According to the USGS, 75 million people in 39 states are subject to “significant risk.”4
Earthquake Magnitude and Intensity
Earthquake magnitude is a number that characterizes the relative size of an earthquake. It was historical y reported
using the Richter scale (magnitudes in this report are generally consistent with the Richter scale). Richter magnitude is
calculated from the strongest seismic wave recorded from the earthquake, and is based on a logarithmic (base 10)
scale: for each whole number increase in the Richter scale, the ground motion increases by 10 times. The amount of
energy released per whole number increase, however, goes up by a factor of 32. The moment magnitude scale is
another expression of earthquake size, or energy released during an earthquake, that roughly corresponds to the
Richter magnitude and is used by most seismologists because it more accurately describes the size of very large
earthquakes. Sometimes earthquakes will be reported using qualitative terms, such as Great or Moderate. Generally,
these terms refer to magnitudes as follows: Great (M>8); Major (M>7); Strong (M>6); Moderate (M>5); Light (M>4);
Minor (M>3); and Micro (M<3).
Intensity is a measure of how much shaking occurred at a site based on observations and amount of damage. Intensity
is usually reported on the Modified Mercalli Intensity Scale as a Roman numeral ranging from I (not felt) to XII (total
destruction). The intensity of an earthquake depends on where the earthquake occurs, how it is felt by people, and
the damage it causes. The lower numbers of the Modified Mercalli Intensity Scale generally refer to how the
earthquake is felt by people, and the higher numbers are based on observed structural damage.
Modified Mercalli intensities that are typically observed at locations near the epicenters of earthquakes of different
magnitudes are as follows:
Magnitude 1.0-3.0 Modified Mercalli Intensity I
Magnitude 3.0-3.9 Modified Mercalli Intensity II-III
Magnitude 4.0-4.9 Modified Mercalli Intensity IV-V
Magnitude 5.0-5.9 Modified Mercalli Intensity VI-VII
Magnitude 6.0-6.9 Modified Mercalli Intensity VII-IX
Magnitude 7.0+ Modified Mercalli Intensity VIII or higher
Source: USGS FAQs, at http://earthquake.usgs.gov/learn/faq/; and Magnitude/Intensity Comparison, at
http://earthquake.usgs.gov/learn/topics/mag_vs_int.php.
2008 Update to the National Seismic Hazard Map
On April 21, 2008, the USGS released National Seismic Hazards Maps that updated the version
published in 2002.5 Compared to the 2002 version, the new maps indicate lower ground motions
(by 10% to 25%) for the central and eastern United States, based on modifications to the ground-
motion models used for earthquakes. The new maps indicate that estimates of ground motion for
the western United States are as much as 30% lower for certain types of ground motion, called
long-period seismic waves, which affect taller, multi-story buildings. Ground motion that affects
4 U.S. Geological Survey, Dept. of the Interior, Earthquake Hazards—A National Threat, Fact Sheet 2006-3016,
March 2006, http://pubs.usgs.gov/fs/2006/3016/2006-3016.pdf. During the period 1975-1995, only four states did not
experience detectable earthquakes: Florida, Iowa, North Dakota, and Wisconsin. See USGS Earthquake Hazards
Program, Earthquake Facts, at http://earthquake.usgs.gov/learn/facts.php.
5 USGS Fact Sheet 2008-3018, “2008 United States National Seismic Hazard Maps” (April 2008), at
http://pubs.usgs.gov/fs/2008/3018/pdf/FS08-3018_508.pdf;
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shorter buildings of a few stories, called short-period seismic waves, is roughly similar to the
2002 maps. The new maps show higher estimates for ground motion for western Oregon and
Washington compared to the 2002 maps, due to new ground motion models for the offshore
Cascadia subduction zone. In formulating the 2008 maps, the USGS gave more weight to the
probability of a catastrophic magnitude 9 earthquake occurring along the Cascadia subduction
zone. The Cascadia subduction zone fault ruptures, on average, every 500 years, and has the
potential to generate destructive earthquakes and tsunamis along the coasts of Washington,
Oregon, and northern California.
Earthquake Forecast for California
According to a report released on April 14, 2008, California has a 99% chance of experiencing a
magnitude 6.7 or larger earthquake in the next 30 years.6 The likelihood of an even larger
earthquake, magnitude 7.5 or greater, is 46%, and such an earthquake would likely occur in the
southern part of the state. The fault with the highest probability of generating at least one
earthquake of magnitude 6.7 or greater over the next 30 years is the San Andreas in southern
California (59% probability); for northern California it is the Hayward-Rodgers Creek fault
(31%). The earthquake forecasts are not predictions (i.e., they do not give a specific date or time),
but represent probabilities over a given time period. In addition, the probabilities have variability
associated with them. The earthquake forecasts are known as the “Uniform California Earthquake
Rupture Forecast (UCERF)” and are produced by a working group composed of the USGS, the
California Geological Survey, and the Southern California Earthquake Center.
How Many Earthquakes Occur Each Year?
The USGS estimates that several million earthquakes occur worldwide each year, but the majority
are of small magnitude or occur in remote areas, and are not detectable. More earthquakes are
detected each year as more seismometers7 are installed in the world, but the number of large
earthquakes (magnitude greater than 6.0)8 has remained relatively constant. Between 2000 and
2008 there were between 2,261 and 3,876 earthquakes per year in the United States, according to
the National Earthquake Information Center (NEIC). (See Figure 3.)
As Figure 3 shows, about 98% of earthquakes detected each year by the NEIC are smaller than
magnitude 5.0 (light earthquakes); only 63 earthquakes exceeded magnitude 6.0 (strong
earthquakes) for the 10-year period (about 0.2% of the total earthquakes detected), for an average
of about six earthquakes per year of at least 6.0 magnitude. Larger earthquakes, although
infrequent, cause the most damage and are responsible for most earthquake-related deaths. The
great San Francisco earthquake of 1906 claimed an estimated 3,000 lives, as a result of both the
earthquake and subsequent fires. Over the past 100 years, relatively few Americans have died as a
result of earthquakes, compared to citizens in some other countries.9 Since 1970, three strong
6 USGS Fact Sheet 2008-3027, “Forecasting California’s Earthquakes—What Can We Expect in the Next 30 Years?”
(2008), at http://pubs.usgs.gov/fs/2008/3027/fs2008-3027.pdf.
7 Seismometers are instruments that measure and record the size and force of seismic waves, essentially sound waves
radiated from the earthquake as it ruptures. Seismometers generally consist of a mass attached to a fixed base. During
an earthquake, the base moves and the mass does not, and the relative motion is commonly transformed into an
electrical voltage that is recorded. A seismograph usually refers to the seismometer and the recording device, but the
two terms are often used interchangeably.
8 See USGS “Earthquakes Facts and Statistics” at http://neic.usgs.gov/neis/eqlists/eqstats.html#table_2.
9 Estimates of earthquake-related fatalities vary, and an exact tally of deaths and injuries is rare. For more information
(continued...)
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earthquakes (greater than magnitude 6) in the United States were responsible for 188 of the 212
total earthquake-related fatalities. (See Table 2.)
Figure 3. Histogram of the Number of U.S. Earthquakes
from 2000 to 2009 by Magnitude (1.0 to 6.9)
2500
2000
rthquakes
1500
a
1000
of E
ber
500
m
u
N
0
1.0 to
2.0 to
3.0 to
4.0 to
5.0 to
6.0 to
1.9
2.9
3.9
4.9
5.9
6.9
Magnitude
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Source: USGS, “Earthquake Facts and Statistics,” at http://neic.usgs.gov/neis/eqlists/eqstats.html; data as of
January 6, 2011.
Note: Earthquakes greater than magnitude 7.0 and less than 1.0 are not shown. According to the USGS, 6
earthquakes of magnitude 7.0 or greater occurred in the United States between 2000 and 2009.
Table 2. Earthquakes Responsible for Most U.S. Fatalities Since 1970
Date Location
Magnitude
Deaths
February 9, 1971
San Fernando Val ey, CA
6.6
65
October 18, 1989
Loma Prieta, CA
6.9
63
January 17, 1994
Northridge, CA
6.7
60
Source: USGS, http://earthquake.usgs.gov/earthquakes/states/us_deaths.php.
Note: Other sources report different numbers of fatalities associated with the Northridge earthquake.
Earthquake Fatalities
Since 2000, only two deaths directly caused by earthquakes have occurred in the United States,
both associated with falling debris in Paso Robles (CA) during the December 22, 2003, San
Simeon earthquake of magnitude 6.5. In contrast, earthquakes have been directly or indirectly
responsible for more than 685,000 fatalities in other countries since 2000.10 Approximately 65%
(...continued)
on the difficulties of counting earthquake-related deaths and injuries, see http://earthquake.usgs.gov/regional/world/
casualty_totals.php.
10 U.S. Geological Survey, Earthquakes with 1,000 or More Deaths Since 1900, at http://earthquake.usgs.gov/
earthquakes/world/world_deaths.php. This estimate does not include fatalities from the February 27, 2010, magnitude
8.8 Chilean earthquake, which has resulted in widespread destruction but few fatalities compared to the Indonesian,
(continued...)
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of those estimated deaths resulted from the December 2004 Indonesian earthquake (and resulting
tsunami) of magnitude 9.1, and the January 2010 magnitude 7.0 earthquake in Haiti.
Estimating Potential Losses from Earthquakes
Estimating the seismic hazard for a region—as in Figure 2—is a first step in assessing risk. As a
second step, shaking hazards maps are often combined with other data, such as the strength of
existing buildings, to estimate possible damage in an area due to an earthquake. A third step in
estimating potential losses would be in assigning value to the infrastructure at risk from
earthquake damage. The combination of seismic risk, population, and vulnerable infrastructure
can help improve the understanding of which urban areas across the United States face risks from
earthquake hazards that may not be immediately obvious from the probability maps of shaking
hazards alone, and what potential economic costs may be at stake.
The 1994 Northridge earthquake was the nation’s most damaging earthquake in the past 100
years, preceded five years earlier by the second-most costly earthquake—Loma Prieta.
Comparing losses between different earthquakes, and between earthquakes and other disasters
such as hurricanes, can be difficult because of the different ways losses are calculated.
Calculations may include a combination of insured losses, uninsured losses, and estimates of lost
economic activity.
The United States faces potentially large total losses due to earthquake-caused damage to
buildings and infrastructure and lost economic activity. As urban development continues in
earthquake-prone regions in the United States, concerns are increasing about the exposure of the
built environment, including utilities and transportation systems, to potential earthquake
damage.11 One estimate of economic loss from a severe earthquake in the Los Angeles area is
over $500 billion.12 Another estimate of economic loss from a hypothetical 6.5 magnitude
earthquake along the heavily populated central New Jersey-Philadelphia corridor would be even
higher—approximately $900 billion. The seismic hazard in the New Jersey-Philadelphia regions,
however, is much lower than in the Los Angeles area, as shown in Figure 2.
Another approach to estimating potential losses is to “normalize” the damage estimates from past
earthquakes by adjusting for inflation, increases in wealth, and changes in population. For
example, adjusting the 1906 San Francisco earthquake and subsequent fire using 2005 dollars
results in between $39 billion and $328 billion in losses, depending on assumptions and
earthquake mitigation measures if that earthquake happened today.13
(...continued)
Pakistan, and Haiti earthquakes.
11 FEMA Publication 366, HAZUS MH Estimated Annualized Earthquake Losses for the United States (April 2008), at
http://www.fema.gov/library/viewRecord.do?id=3265. Hereafter referred to as FEMA 366.
12 A. M. Best Company Inc., 2006 Annual Earthquake Study: $100 Billion of Insured Loss in 40 Seconds (Oldwick, NJ:
A.M. Best Company, 2006), p. 12. The A. M. Best report includes estimates from catastrophe-modeling companies of
predicted damage from hypothetical earthquakes in Los Angeles, the Midwest, the Northeast, and Japan. The report
cites an estimate by one such company, Risk Management Solutions (RMS), that a hypothetical 7.4 magnitude event
along the Newport-Inglewood Fault near Los Angeles would cause $549 billion in total property damage. A
hypothetical 6.5 magnitude earthquake along a fault between Philadelphia and New York City would produce $901
billion in total loss, according to an RMS estimate.
13 Kevin Vranes and Roger Pielke, Jr., “Normalized Earthquake Damage and Fatalities in the United States: 1900-
(continued...)
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Some studies and techniques combine seismic risk with the value of the building inventory14 and
income losses (e.g., business interruption, wage, and rental income losses) in cities, counties, or
regions across the country to provide estimations of economic losses from earthquakes. An April
2008 report from FEMA calculated that the average annualized loss from earthquakes nationwide
is $5.3 billion, with California, Oregon, and Washington accounting for nearly $4.1 billion (77%)
of the U.S. total estimated average annualized loss.15 Table 3 shows metropolitan areas with
estimated average annualized U.S. earthquake losses over $10 million.
Table 3. U.S. Metropolitan Areas with Estimated Annualized Earthquake Losses of
More Than $10 Million
(in $ millions)
Rank Metro
area
AEL Rank Metro
area
AEL
1
Los Angeles-Long Beach-Santa Ana, CA
$1,312
23
Reno-Sparks, NV
$29
2
San Francisco-Oakland-Fremont, CA
$781
24
Charleston-North Charleston, SC
$22
3
Riverside-San Bernadino-Ontario, CA
$397
25
Columbia, SC
$22
4
San Jose-Sunnyvale-Santa Clara, CA
$277
26
Stockton, CA
$21
5
Seattle-Tacoma, WA
$244
27
Atlanta-Sandy Springs-Marietta, GA
$19
6
San Diego-Carlsbad-San Marcos, CA
$155
28
Bremerton-Silverdale, WA
$18
7 Portland-Vancouver-Carlsbad,
OR
$137 29 Ogden-Clearfield,
UT
$18
8
Oxnard-Thousand Oaks-Ventura, CA
$111
30
Salem, OR
$17
9
Santa Rosa-Petaluma, CA
$69
31
Eugene-Springfield, OR
$17
10
St. Louis, MO-IL
$59
32
Napa, CA
$16
11
Salt Lake City, UT
$52
33
San Luis Obispo-Paso Robles, CA
$16
12 Sacramento-Arden-Arcade-Roseville,
CA $52 34 Nashville-Davidson-Murfreesboro,
TN
$15
13 Val ejo-Fairfield,
CA
$40 35 Albuquerque,
NM
$15
14 Memphis,
TN
$38 36 Olympia,
WA
$14
15
Santa Cruz-Watsonville, CA
$36
37
Modesto, CA
$13
16 Anchorage,
AK
$35 38 Fresno,
CA
$13
17
Santa Barbara-Santa Maria-Goleta, CA
$34
39
Evansville, IN-KY
$12
18 Las
Vegas-Paradise,
NV
$33 40 Birmingham-Hoover,
AL
$11
19 Honolulu,
HI
$32 41 El
Centro,
CA
$11
20
Bakersfield, CA
$30
42
Little Rock-North Little Rock, AR
$11
21
New York-Northern New Jersey-
$30 43 Provo-Orem,
UT
$10
Long Island, NY
22 Salinas,
CA
$29
Source FEMA Publication 366, HAZUS MH Estimated Annualized Earthquake Losses for the United States (April
2008). Annualized earthquake losses (AEL) calculated in 2005 dol ars.
(...continued)
2005,” Natural Hazards Review, vol. 10, no. 3 (August 2009), pp. 84-101.
14 Building inventory refers to four main inventory groups: (1) general building stock, (2) essential and high potential
loss facilities, (3) transportation systems, and (4) utility systems (FEMA 366).
15 FEMA 366, p. 37.
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Annualized earthquake loss (AEL) addresses two components of seismic risk: the probability of
ground motion and the consequences of ground motion. It enables comparison between different
regions with different seismic hazards and different building construction types and quality. For
example, earthquake hazard is higher in the Los Angeles area than in Memphis, but the general
building stock in Los Angeles is more resistant to the effects of earthquakes. The AEL annualizes
the expected losses by averaging them by year.
A single large earthquake can cause far more damage than the average annual estimate.
Annualized estimates, however, help provide comparisons of infrequent, high-impact events like
damaging earthquakes with more frequently occurring hazards like floods, hurricanes, or other
types of severe weather. The annualized earthquake loss values shown in Table 3 represent future
estimates, and are calculated by multiplying losses from potential future ground motions by their
respective frequencies of occurrence, and then summing these values.16
Table 3 also shows that annualized earthquake losses in the New York-Northern New Jersey-
Long Island metropolitan area are $30 million (ranked 21 out of 43 metropolitan areas with losses
greater than $1 million per year), even though no destructive earthquakes have struck that area for
generations.17 This area has a relatively low seismic hazard, but also has an extensive
infrastructure and is densely populated. That combination of seismic risk, extensive
infrastructure, and dense population produces a significant risk to people and structures,
according to some estimates.18
A Decrease in Estimated Loss?
In its most recent publication estimating potential earthquake losses, FEMA noted that the $5.3
billion in annualized earthquake loss nationwide was 21% higher than the $4.4 billion calculated
in FEMA’s previous report, published in February 2001.19 However, the 2001 report calculated
losses using 1994 dollars, and when adjusted to reflect 2005 dollars the earlier estimate increased
to $5.6 billion, indicating a small decrease in nationwide annualized earthquake loss potential
since the 2001 report was published. According to FEMA, this loss occurred even though the
national building inventory increased by 50% over this same period.
What factors led to a decreased estimate in potential loss despite growth in building inventory?
According to FEMA, two primary factors were responsible: (1) a slight decrease in estimated
earthquake hazard in the western United States (namely California) except for some parts of
Washington and Utah, and (2) a change in the distribution of building inventory in California,
with an increase in wood frame buildings of 17% and a reduction in the amount of masonry
(-6%), steel (-5.8%), and concrete (-3%) buildings in the state.20 Wood frame buildings are less
vulnerable to earthquake damage, generally, compared to other construction types. Because
California accounts for 66% of the overall nationwide annualized earthquake loss, a 17% increase
16 FEMA 366, p. 10.
17 The largest earthquakes in New York, New Jersey, and Massachusetts were, respectively: 1944, Massena, NY,
magnitude 5.8, felt from Canada south to Maryland; 1783, New Jersey, magnitude 5.3, felt from New Hampshire to
Pennsylvania; and 1755, Cape Ann and Boston, MA, intensity of VIII on the Modified Mercalli Scale, felt from Nova
Scotia to Chesapeake Bay (USGS Earthquake Hazards Program).
18 USGS Circular 1188, Table 3.
19 FEMA 366, p. 32.
20 Ibid., p. 32 and p. 36.
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in wood frame buildings had a proportionally large effect. In fact, FEMA attributed 78% of the
loss reduction between 2001 and 2008 to the change in building inventory distribution, and 22%
to the decrease in earthquake hazard for California.21
The New Madrid Seismic Zone
The New Madrid Seismic Zone in the central United States is vulnerable to large but infrequent
earthquakes. A series of large (magnitude greater than 7.0) earthquakes struck the Mississippi
Valley over the winter of 1811-1812, centered close to the town of New Madrid, MO. Some of
the tremors were felt as far away as Charleston, SC, and Washington, DC. The mechanism for the
earthquakes in the New Madrid zone is poorly understood,22 and no earthquakes of comparable
magnitude have occurred in the area since these events.
Estimating earthquake damage is not an exact science and depends on many factors. As described
above, these are primarily the probability of ground motion occurring in a particular area (see
Figure 2), and the consequences of that ground motion, which are largely a function of building
construction type and quality, and of the level of ground motion and shaking during the actual
event. Such factors contribute to the difficulty of making a reasonable damage estimate for a low-
frequency, high-impact event in the New Madrid region based on the probability of an earthquake
of similar magnitude occurring. This uncertainty has implications for policy decisions to
ameliorate risk, such as setting building codes, and for designing and building structures to
withstand a level of shaking commensurate with the risk. Presumably, the same seismic hazard
should lead to similar building codes in urban areas (e.g., in Figure 2, compare the seismic
hazard for the New Madrid area with portions of California).
Some researchers have questioned whether erring on the side of caution in the New Madrid
Seismic Zone is justified.23 These researchers challenge whether the benefits of building
structures to conform with the earthquake probability estimates merit the costs, in light of the
uncertainty in making those probability estimates.24 These analyses may call into question
whether the probability of ground motion estimates for the New Madrid Seismic Zone (the bulls-
eye-shaped area shown in Figure 2 that includes parts of Arkansas, Illinois, Tennessee, and
Missouri), and other regions of the country that experience infrequent earthquakes, are too high.25
A contributing factor to the uncertainty in estimating the earthquake hazard in the New Madrid
Seismic Zone is the small amount of ground motion measured across the major faults, compared
to much faster motions measured across major faults in California.26 Typically, seismologists
21 Ibid., p. 36.
22 In contrast to California, where earthquakes occur on the active margin of the North American tectonic plate, the
New Madrid seismic zone is not on a plate boundary but may be related to old faults in the interior of the plate,
marking a zone of tectonic weakness.
23 Andrew Newman et al., “Slow Deformation and Lower Seismic Hazard in the New Madrid Seismic Zone,” Science,
v. 284 (April 23, 1999), pp. 619-621.
24 Seth Stein, Joseph Tomasello, and Andrew Newman, “Should Memphis Build for California’s Earthquakes?” Eos, v.
84, no. 19, (May 13, 2003), pp. 177, 184-185.
25 Seth Stein, “Code Red: Earthquake Imminent?” Earth, vol. 54, no. 1 (January 2009), pp. 52-59.
26 Some researchers measure, for example, less than 2 millimeters of ground motion per year in the New Madrid
Seismic Zone using modern GPS technology. In contrast, motion across the San Andreas Fault in California is about 36
millimeters per year. See Seth Stein, Disaster Deferred: How New Science is Changing Our View of Earthquake
Hazards in the Midwest (New York: Columbia University Press, 2010), pp. 4-5.
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estimate the stress that builds up on a fault by measuring ground motion across the fault: the
faster the motion, the more quickly the stress builds up. The buildup of stress may be ultimately
released in an earthquake during which the rocks on one side of the fault move relative to the
other side. Generally, for fast-moving faults such as the San Andreas Fault, the period of
earthquake recurrence is short compared to faults where the ground motion is relatively slow.
Yet despite the uncertainty raised by some researchers because of the apparent lack of much
ground motion, the USGS attributes a seismic hazard to areas of the New Madrid Seismic Zone
comparable to the most seismically active portions of California (see Figure 2), where
earthquakes are much more frequent, and the mechanisms for generating earthquakes are better
understood. The lack of much ground motion is a confusing factor for scientists trying to
understand the New Madrid Seismic Zone, which experienced three major earthquakes 200 years
ago but does not seem to exhibit much ground motion today. In part because of the 200th
anniversary of the three major earthquakes, FEMA is planning a National Level Exercise (NLE
2011) that will focus on a scenario of a catastrophic earthquake in the New Madrid Seismic Zone
and will encompass eight states: Alabama, Arkansas, Kentucky, Illinois, Indiana, Mississippi,
Missouri, and Tennessee. The NLE 2011 will be conducted in May 2011.27
Earthquakes in Haiti and Chile—Some Comparisons
The magnitude 8.8 earthquake that struck Chile on February 27, 2010, was over 60 times larger
than the magnitude 7.0 earthquake that destroyed Port-au-Prince, Haiti, less than two months
earlier. Yet the number of deaths and the amount of damage in Haiti far exceeded damage and
fatalities in Chile. The Chile earthquake occurred offshore, and was deeper and farther away from
major cities than the Haiti earthquake; in addition, the infrastructure in Chile—buildings,
highways, bridges—appears to have been built to withstand earthquake shaking far better than
similar infrastructure in Haiti. Both countries faced significant seismic hazards, although the
hazard facing Chile was arguably better known because Chile experienced a great (magnitude
9.5) earthquake in 1960,28 and Haiti last experienced a large earthquake in 1860 (earthquakes in
1751 and 1770 destroyed Port-au-Prince; the 1860 earthquake struck farther west). In addition to
the seismic hazard, which is a consequence of geology and plate tectonics, Haiti’s vulnerability to
earthquake shaking appears to have exceeded Chile’s. Tragically, Haiti was at greater risk of
damage and resulting fatalities than Chile, even for an earthquake of much smaller magnitude.
January 12, 2010, Magnitude 7.0 Earthquake in Haiti
On Tuesday, January 12, 2010, a magnitude 7.0 earthquake struck Haiti at 4:53 p.m. The
epicenter was located approximately 15 miles west-southwest of Port-au-Prince, and the
earthquake occurred at a depth of about 8 miles, according to the USGS.29 The relatively shallow
earthquake, and its close proximity to the capital city, exposed millions of Haitians to severe to
violent ground shaking. The earthquake occurred along the Enriquillo-Plantain Garden fault
system, a major east-west trending strike-slip fault system that lies between the Caribbean
27 See FEMA, National Level Exercise NLE 2011 Private Sector Participation, at http://www.fema.gov/privatesector/
take_action.shtm#2.
28 According to the USGS, the May 22, 1960, magnitude 9.5 earthquake was the largest earthquake in the world. See
http://earthquake.usgs.gov/earthquakes/world/events/1960_05_22.php.
29 USGS Earthquake Hazards Program, at http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010rja6/.
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tectonic plate and the North American tectonic plate; the Caribbean plate actively moves against
the North American plate and shear stresses are created at the boundary. At a strike-slip fault, the
rocks move past each other horizontally along the fault line (in contrast to a thrust fault, where
rocks on one side of the fault move on top of the rocks on the other side). Other examples of
strike-slip faults are the San Andreas fault in California and the Red River fault in China.
The January 12, 2010, earthquake caused widespread damage in the Port-au-Prince area, causing
approximately 223,000 deaths and 300,000 injuries.30 Also, a series of aftershocks followed the
main earthquake. There were 14 aftershocks greater than magnitude 5, and 36 greater than
magnitude 4, within the first day following the magnitude 7.0 event. Aftershocks have the
potential to cause further damage, especially to structures weakened by the initial large
earthquake. The USGS noted that buildings in the Port-au-Prince area will continue to be at risk
from strong earthquake shaking, and that the fault responsible for the January 12, 2010,
earthquake still stores sufficient strain to be released as a large, damaging earthquake during the
lifetime of structures built during the reconstruction effort.31
The USGS based its probability estimates on techniques developed to assess earthquake hazards
in the United States. Using these techniques, the USGS estimated that the probability of a
magnitude 7 or greater earthquake occurring within the next 50 years along the Enriquillo fault
near Port-au-Prince is between 5% and 15%. The range of probabilities reflects the current
understanding of the seismicity and tectonics of the Haiti region. By comparison, the USGS has
estimated that that the probability of a magnitude 7 or greater earthquake occurring within the
next 50 years along the Hayward-Rodgers Creek fault east of San Francisco is about 15%.32
February 27, 2010, Magnitude 8.8 Earthquake in Chile
A magnitude 8.8 earthquake struck Chile on February 27, 2010, along a subduction zone plate
boundary fault 65 miles north-northeast of the city of Concepcion and offshore of the Chilean
coast.33 The earthquake occurred at a depth of approximately 22 miles below the seafloor, much
deeper than the earthquake that struck Haiti on January 12, 2010. The city of Concepcion
experienced intensity IX shaking on the Modified Mercalli Intensity Index, corresponding to
considerable damage to specially designed structures, and corresponding to great damage to
“substantial” buildings. The capital city of Santiago, located 200 miles northeast of the epicenter,
experienced intensity VIII shaking corresponding to considerable damage in ordinary substantial
buildings.34 The earthquake caused an estimated $30 billion in total economic damage.35 Over
500 deaths were reported, many from the tsunami generated by the subsea earthquake, and
approximately 1.8 million people were affected.
Because the earthquake occurred offshore, it generated a tsunami, which struck parts of the
Chilean coastline and offshore islands, causing damage and fatalities. Tsunami warnings were
30 See http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010rja6/#summary.
31 USGS statement, “USGS Updates Assessment of Earthquake Hazard and Safety in Haiti and the Caribbean,”
February 23, 2010, at http://www.usgs.gov/newsroom/article.asp?ID=2413&from=rss_home.
32 Ibid. However, the USGS also notes that the probability of a magnitude 6.7 or greater earthquake occurring on the
Hayward-Rodgers fault over the next 30 years is 31%.
33 See http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010tfan/#details.
34 See http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010tfan/#summary.
35 Ibid.
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issued by the National Weather Service Pacific Tsunami Warning Center for Hawaii, Japan, and
other regions bordering the Pacific Ocean that may have been vulnerable to a damaging tsunami
wave, although most regions far from the epicenter did not experience any serious damage. A
tsunami caused significant damage to the city of Hilo, Hawaii, following the May 1960
magnitude 9.5 earthquake that also occurred along the subduction zone fault about 143 miles
south of the February 27, 2010, earthquake.36 Why the 1960 earthquake generated a tsunami that
caused damage and fatalities in Hawaii, Japan, and the Philippines, while the 2010 earthquake did
not, is not yet well understood and is being actively studied.
The magnitude 8.8 earthquake occurred along the boundary between the Nazca tectonic plate and
the South American tectonic plate, which converge at a rate of about 3 inches per year. The Nazca
plate is subducting under the South American plate, which rides over the top of the Nazca plate.
In geologic terms, this is known as a thrust fault or megathrust, in contrast to a strike-slip fault,
where the rocks on either side of the fault slide past each other. The San Andreas fault and the
Enriquillo fault that caused the January 2010 Haiti earthquake are strike-slip faults. The
Sumatran-Andaman megathrust fault, which triggered the December 2004 Indonesian earthquake
and tsunami, is a subduction zone fault or megathrust geologically similar to the Nazca-South
American tectonic plate subduction zone.
Is There a Similar Risk to the United States?
Subduction zone megathrust faults generate the largest earthquakes in the world. The Cascadia
Subduction Zone megathrust that stretches from mid-Vancouver Island in southern British
Columbia southward to Cape Mendocino in northern California has the potential to generate a
very large earthquake, similar in magnitude to the February 2010 Chilean earthquake. The fault’s
proximity to the northwestern U.S. coastline—approximately 50-100 miles offshore—also poses
a significant tsunami hazard; destructive waves from a large earthquake along the fault could
reach the coast of Oregon and Washington in less than an hour, possibly in tens of minutes. The
Cascadia Subduction Zone fault forms the boundary between the subducting Juan de Fuca
tectonic plate and the overriding North American plate, very similar to the relationship between
the Nazca Plate and the South American Plate off the Chilean coast. If the Cascadia Subduction
Zone megathrust were to “unzip” or rupture along a large section of its entire length, models
indicate that it would likely generate a megathrust earthquake near magnitude 9 or more, similar
to the 1964 Alaskan earthquake, the 1960 and 2010 Chilean earthquakes, and the 2004 Indonesian
earthquake. Scientists have documented that the last time this occurred along the Cascadia
Subduction Zone fault was in 1700. The 1700 earthquake spawned a tsunami that traveled across
the Pacific Ocean and struck Japan. Because of the tectonic similarities between the Cascadia
Subduction Zone megathrust and the Nazca-South American plate megathrust, scientists hope to
learn a great deal about the seismic hazard in the Pacific Northwest by studying the unique strong
ground motion recordings from the 2010 Chilean magnitude 8.8 earthquake.
36 The Orphan Tsunami of 1700—Japanese Clues to a Parent Earthquake in North America, USGS, Professional Paper
1707, 2005, http://pubs.usgs.gov/pp/pp1707/.
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Monitoring
Congress authorized the USGS to monitor seismic activity in the United States in the 1990 law
modifying NEHRP (P.L. 101-614). The USGS operates a nationwide network of seismographic
stations called the Advanced National Seismic System (ANSS), which includes the National
Strong-Motion Project (NSMP). Globally, the USGS and the Incorporated Research Institutions
for Seismology (IRIS) operate 140 seismic stations of the Global Seismic Network (GSN) in
more than 80 countries.37 The GSN provides worldwide coverage of earthquakes, including
reporting and research.38
Advanced National Seismic System (ANSS)
According to the USGS, “the mission of ANSS is to provide accurate and timely data and
information products for seismic events, including their effects on buildings and structures,
employing modern monitoring methods and technologies.”39 If fully implemented, ANSS would
encompass more than 7,000 earthquake sensor systems covering portions of the nation that are
vulnerable to earthquake hazards. As envisioned, the system would consist of dense urban
networks, regional networks, and backbone stations.
ANSS Funding
Congress first authorized the ANSS program in P.L. 106-503 at a level of $38 million for FY2002
and $44 million for FY2003. The 2004 reauthorization of NEHRP (P.L. 108-360) authorized $30
million for ANSS in FY2005 and then $36 million per year through FY2009. From FY2000
through FY2010, the USGS has spent a total of $68.2 million on ANSS-directed funding,40
although expenditures have never reached authorized levels since Congress first authorized
appropriations for ANSS. Of the $8.8 million for ANSS-directed funding in FY2009, about $1.5
million was devoted to the development, modernization, and expansion of the system; the
remainder of FY2009 funding was used to operate the existing system.41 By the end of 2009, the
USGS and its partners had installed a cumulative total of 886 ANSS earthquake monitoring
stations.42
The American Recovery and Reinvestment Act (ARRA, P.L. 111-5) provided an additional $19
million for ANSS.43 The ARRA funding for ANSS was provided for modernization of the current
system, and is approximately 70% expended. The remainder of the ARRA funding for ANSS is
expected to be expended by the end of FY2011.44
37 IRIS is a university research consortium, primarily funded by NSF, that collects and distributes seismographic data.
38 The GSN also monitors nuclear explosions.
39 USGS Earthquake Hazards Program, at http://earthquake.usgs.gov/research/monitoring/anss/.
40 USGS FY2011 Budget Justification, p. J-9, at http://www.usgs.gov/budget/2011/greenbook/
FY2011_USGS_Greenbook.pdf.
41 Email from William Leith, Advanced National Seismic System Coordinator, USGS, December 22, 2009.
42 USGS FY2011 Budget Justification, p. J-10.
43 USGS FY2011 Budget Justification, p. J-10.
44 E-mail from William Leith, USGS, January 11, 2011.
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Dense Urban Networks
In the original conception for ANSS, approximately 6,000 of the planned stations would have
been installed in 26 high-risk urban areas to monitor strong ground shaking and how buildings
and other structures respond. Currently, five high-risk urban areas have instruments deployed in
sufficient density to generate the data to produce near real-time maps,45 called ShakeMaps, which
can be used in emergency response during and after an earthquake.46 (See “ShakeMap,” below.)
Backbone Stations
Approximately 100 instruments comprise the existing “backbone” of ANSS, with a roughly
uniform distribution across the United States, including Alaska and Hawaii. These instruments
provide a broad and uniform minimum threshold of coverage across the country. The backbone
network consists of USGS-deployed instruments and other instruments that serve both ANSS and
the EarthScope project (described below, under “National Science Foundation”).
National Strong-Motion Project (NSMP)
Under ANSS, the USGS operates the NSMP to record seismic data from damaging earthquakes in
the United States on the ground and in buildings and other structures in densely urbanized areas.
The program currently has 900 strong-motion47 instruments in 701 permanent stations across the
United States and in the Caribbean. The NSMP has three components: data acquisition, data
management, and research. The near real-time measurements collected by the NSMP are used by
other government agencies for emergency response and real-time warnings. If fully implemented,
the ANSS program would deploy about 3,000 strong-motion instruments. Many of the current
NSMP instruments are older designs and are being upgraded with modern seismometers.
Regional Networks
If ANSS were fully implemented under its original conception, approximately 1,000 new
instruments would replace aging and obsolete stations in the networks that now monitor the
nation’s most seismically active regions. The current regional networks contain a mix of modern,
digital, broadband, and high-resolution instruments that can provide real-time data; they are
supplemented by older instruments that may require manual downloading of data. Universities in
the region typically operate the regional networks and will likely continue to do so as ANSS is
implemented.
45 The five urban areas are Los Angeles, San Francisco, Seattle, Salt Lake City, and Anchorage. E-mail from William
Leith, USGS, February 7, 2011.
46 The number of stations necessary to generate a data-based ShakeMap depends on the urban area and geology, but
roughly correspond to about half the number of planned stations per urban area, at a spacing of about 20 kilometers
between stations. Personal communication, William Leith, USGS, January 11, 2010.
47 Strong motion seismometers, or accelerometers, are special sensors that measure the acceleration of the ground
during large (>6.0 magnitude) earthquakes.
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Global Seismic Network (GSN)
The GSN is a system of broadband digital seismographs arrayed around the globe and designed to
collect high-quality data that are readily accessible to users worldwide, typically via computer.
Currently, 140 stations have been installed in 80 countries and the system is nearly complete,
although in some regions the spacing and location of stations has not fully met the original goal
of uniform spacing of approximately 2,000 kilometers. The system is currently providing data to
the United States and other countries and institutions for earthquake reporting and research, as
well as for monitoring nuclear explosions to assess compliance with the Comprehensive Test Ban
Treaty.
The Incorporated Research Institutions for Seismology (IRIS) coordinates the GSN and manages
and makes available the large amounts of data that are generated from the network. The actual
network of seismographs is organized into two main components, each managed separately. The
USGS operates two-thirds of the stations from its Albuquerque Seismological Laboratory, and the
University of California-San Diego manages the other third via its Project IDA (International
Deployment of Accelerometers). Other universities and affiliated agencies and institutions
operate a small number of additional stations. IRIS, with funding from the NSF, supports all of
the stations not funded through the USGS appropriations. Funding for the GSN is provided via
annual appropriations from the USGS and the National Science Foundation. In addition, the
USGS committed $4.7 million from ARRA funding to the GSN, and NSF committed a similar
portion of its ARRA funding to replace obsolete equipment on GSN stations worldwide.48
Detection, Notification, and Warning
Unlike other natural hazards, such as hurricanes, where predicting the location and timing of
landfall is becoming increasingly accurate, the scientific understanding of earthquakes does not
yet allow for precise earthquake prediction. Instead, notification and warning typically involves
communicating the location and magnitude of an earthquake as soon as possible after the event to
emergency response providers and others who need the information.
Some probabilistic earthquake forecasts are now available that give, for example, a 24-hour
probability of earthquake aftershocks for a particular region, such as California. These forecasts
are not predictions, and are currently intended to increase public awareness of the seismic hazard,
improve emergency response, and increase scientific understanding of the short-term hazard.49 In
the California example, a time-dependent map is created and updated every hour by a system that
considers all earthquakes, large and small, detected by the California Integrated Seismic
Network,50 and calculates a probability that each earthquake will be followed by an aftershock51
48 USGS FY2011 Budget Justification, p. J-32. Annual appropriations for GSN totaled approximately $9 million for
FY2009 and reflect the combined appropriations for USGS and NSF. The USGS portion of annual appropriations in
FY2010 was $5.8 million.
49 USGS Open-File Report 2004-1390, and California 24-hour Aftershock Forecast Map, at
http://pasadena.wr.usgs.gov/step/.
50 The California Integrated Seismic Network is the California region of ANSS; see http://www.cisn.org/.
51 Earthquakes typically occur in clusters, in which the earthquake with the largest magnitude is called the main shock,
events before the main shock are called foreshocks, and those after are called aftershocks. See also
http://pasadena.wr.usgs.gov/step/aftershocks.html.
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that can cause strong shaking. The probabilities are calculated from known behavior of
aftershocks and the possible shaking pattern based on historical data.
When a destructive earthquake occurs in the United States or in other countries, the first reports
of its location, or epicenter,52 and magnitude originate either from the National Earthquake
Information Center (NEIC), or from one of the regional seismic networks that are part of ANSS.
Other organizations, such as universities, consortia, and individual seismologists may also
contribute information about the earthquake after the event. Products such as ShakeMap
(described below) are assembled as rapidly as possible to assist in emergency response and
damage estimation following a destructive earthquake.
National Earthquake Information Center (NEIC)
The NEIC, part of the USGS, is located in Golden, CO. Originally established as part of the
National Ocean Survey (U.S. Department of Commerce) in 1966, the NEIC was made part of the
USGS in 1973. With data gathered from the networks described above and from other sources,
the NEIC determines the location and size of all destructive earthquakes that occur worldwide
and disseminates the information to the appropriate national or international agencies,
government public information channels, news media, scientists and scientific groups, and the
general public.
With the advent of the USGS Earthquake Notification Service (ENS), notifications of earthquakes
detected by the ANSS/NEIC are provided free to interested parties. Users of the service can
specify the regions of interest, establish notification thresholds of earthquake magnitude,
designate whether they wish to receive notification of aftershocks, and even set different
magnitude thresholds for daytime or nighttime to trigger a notification.
The NEIC has long-standing agreements with key emergency response groups, federal, state, and
local authorities, and other key organizations in earthquake-prone regions who receive automated
alerts—typically location and magnitude of an earthquake—within a few minutes of an event in
the United States. The NEIC sends these preliminary alerts by email and pager immediately after
an earthquake’s magnitude and epicenter are automatically determined by computer.53 This initial
determination is then checked by around-the-clock staff who confirm and update the magnitude
and location data.54 After the confirmation, a second set of notifications and confirmations are
triggered to key recipients by email, pager, fax, and telephone.
For earthquakes outside the United States, the NEIC notifies the State Department Operations
Center, and often sends alerts directly to staff at American embassies and consulates in the
affected countries, to the International Red Cross, the U.N. Department of Humanitarian Affairs,
and other recipients who have made arrangements to receive alerts.
52 The epicenter of an earthquake is the point on the earth’s surface directly above the hypocenter. The hypocenter is
the location beneath the earth’s surface where the fault rupture begins.
53 Stuart Simkin, NEIC, Golden, CO, telephone conversation, Nov. 4, 2006.
54 In early 2006, the NEIC implemented an around-the-clock operation center and seismic event processing center in
response to the Indonesian earthquake and resulting tsunami of December 2004. Funding to implement 24/7 operations
was provided by P.L. 109-13.
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ShakeMap
Traditionally, the information commonly available following a destructive earthquake has been
epicenter and magnitude, as in the data provided by the NEIC described above. Those two
parameters by themselves, however, do not always indicate the intensity of shaking and extent of
damage following a major earthquake. Recently, the USGS developed a product called ShakeMap
that provides a nearly real-time map of ground motion and shaking intensity following an
earthquake in areas of the United States where the ShakeMap system is in place. Figure 4 shows
an example of a ShakeMap.
The maps produced portray the extent of damaging shaking and can be used by emergency
response and for estimating loss following a major earthquake. Currently, ShakeMaps are
available for northern California, southern California, the Pacific Northwest, Nevada, Utah,
Hawaii, and Alaska.55
With improvements to the regional seismographic networks in the areas where ShakeMap is
available, new real-time telemetry from the region, and advances in digital communication and
computation, ShakeMaps are now triggered automatically and made available within minutes of
the event via the web. In addition, better maps are now available because of recent improvements
in understanding the relationship between the ground motions recorded during the earthquake and
the intensity of resulting damage. If databases containing inventories of buildings and lifelines are
available, they can be combined with shaking intensity data to produce maps of estimated
damage. The ShakeMaps have limitations, especially during the first few minutes following an
earthquake before additional data arrive from distributed sources. Because they are generated
automatically, the initial maps are preliminary, and may not have been reviewed by experts when
first made available. They are considered a work in progress, but are deemed to be very
promising, especially as more modern seismic instruments are added to the regional networks
under ANSS and computational and telecommunication abilities improve.
Prompt Assessment of Global Earthquakes for Response (PAGER)
Another USGS product that is designed to provide nearly real-time earthquake information to
emergency responders, government agencies, and the media is the Prompt Assessment of Global
Earthquakes for Response, or PAGER, system.56 This automated system rapidly assesses the
number of people, cities, and regions exposed to severe shaking by an earthquake, and generally
makes results available within 30 minutes. Following the determination of earthquake location
and magnitude, the PAGER system calculates the degree of ground shaking using the
methodology developed for ShakeMap, estimates the number of people exposed to various levels
of shaking, and produces a description of the vulnerability of the exposed population and
infrastructure. The vulnerability includes potential for earthquake-triggered landslides, which
could be devastating, as was the case for the huge May 12, 2008, earthquake in Sichuan, China.
The automated and rapid reports produced by the PAGER system provide an advantage compared
to the traditional accounts from eye-witnesses on the ground or media reports, because
communications networks may have been disabled from the earthquake. Emergency responders,
55 ShakeMaps for some areas outside the United States are also available. See http://earthquake.usgs.gov/eqcenter/
shakemap/.
56 See the USGS Earthquakes Hazards Program for more information, at http://earthquake.usgs.gov/earthquakes/pager/.
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relief organizations, and government agencies could make plans based on PAGER system reports
even before getting “ground-truth” information from eye-witnesses and the media.57 Figure 5
shows an example of PAGER output for the January 12, 2010, magnitude 7.0 earthquake in Haiti.
Figure 4. Example of a ShakeMap
Source: USGS, http://earthquake.usgs.gov/eqcenter/shakemap/nc/shake/71338066/.
Note: Earthquake occurred 23.1 miles west-northwest of Ferndale, CA, at 4:27 p.m. on January 9, 2010, with a
magnitude of 6.5. The star indicates the epicenter of the earthquake. Viewed on January 12, 2010.
57 See also USGS Fact Sheet 2007-3101 at http://pubs.usgs.gov/fs/2007/3101/.
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Figure 5. Example of PAGER Output for the January 12, 2010,
Magnitude 7.0 Haiti Earthquake
Source: USGS, http://earthquake.usgs.gov/earthquakes/pager/events/us/2010rja6/onepager.pdf.
Note: This is version 7 of the PAGER output, accessed on January 14, 2010.
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Pre-disaster Planning: HAZUS-MH
FEMA developed a methodology and software program called the Hazards U.S. Multi-Hazard
(HAZUS-MH).58 The program allows a user to estimate losses from damaging earthquakes,
hurricane winds, and floods before a disaster occurs. The pre-disaster estimates could provide a
basis for developing mitigation plans and policies, preparing for emergencies, and planning
response and recovery. HAZUS-MH combines existing scientific knowledge about earthquakes
(for example, ShakeMaps, described above), engineering information that includes data on how
structures respond to shaking, and geographic information system (GIS) software to produce
maps and display hazards data including economic loss estimates. The loss estimates produced by
HAZUS-MH include
• physical damage to residential and commercial buildings, schools, critical
facilities, and infrastructure;
• economic loss, including lost jobs, business interruptions, repair and
reconstruction costs; and
• social impacts, including estimates of shelter requirements, displaced households,
and number of people exposed to the disaster.
In addition to furnishing information as part of earthquake mitigation efforts, HAZUS-MH can
also be used to support real-time emergency response activities by state and federal agencies after
a disaster. Twenty-seven HAZUS-MH user groups—cooperative ventures among private, public,
and academic organizations that use the HAZUS-MH software—have formed across the United
States to help foster better-informed risk management for earthquakes and other natural hazards.59
Research—Understanding Earthquakes
U.S. Geological Survey
Under NEHRP, the USGS has responsibility for conducting targeted research into improving the
basic scientific understanding of earthquake processes. The current earthquake research program
at the USGS covers six broad categories:60
• Borehole geophysics and rock mechanics: studies to understand heat flow, stress,
fluid pressure, and the mechanical behavior of fault-zone materials at
seismogenic61 depths to yield improved models of the earthquake cycle;
• Crustal deformation: studies of the distortion or deformation of the earth’s
surface near active faults as a result of the motion of tectonic plates;
• Earthquake geology and paleoseismology: studies of the history, effects, and
mechanics of earthquakes;
• Earthquake hazards: studies of where, why, when, and how earthquakes occur;
58 See http://www.fema.gov/plan/prevent/hazus/hz_overview.shtm.
59 See http://www.hazus.org/.
60 See http://earthquake.usgs.gov/research/.
61 Seismogenic means capable of generating earthquakes.
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• Regional and whole-earth structure: studies using seismic waves from
earthquakes and man-made sources to determine the structure of the planet
ranging from the local scale, to the whole crust, mantle, and even the earth’s
core; and
• Strong-motion seismology, site response, and ground motion: studies of large-
amplitude ground motions and the response of engineered structures to those
motions using accelerometers.
National Science Foundation
NSF supports fundamental research into understanding the earth’s dynamic crust. Through its
Earth Sciences Division (part of the Geosciences Directorate), NSF distributes research grants
and coordinates programs investigating the crustal processes that lead to earthquakes around the
globe.62
EarthScope
In 2003, NSF initiated a Major Research Equipment and Facilities Construction (MREFC) project
called EarthScope that deploys instruments across the United States to study the structure and
evolution of the North American Continent, and to investigate the physical processes that cause
earthquakes and volcanic eruptions.63 EarthScope is a multi-year project begun in 2003 that is
funded by NSF and conducted in partnership with the USGS and NASA.
EarthScope instruments are intended to form a framework for broad, integrated studies of the
four-dimensional (three spatial dimensions, plus time) structure of North America. The project is
divided into three main programs:
• The San Andreas Fault Observatory at Depth (SAFOD), a deep borehole
observatory drilled through the San Andreas fault zone close to the hypocenter of
the 1966 Parkfield, CA, magnitude 6 earthquake;
• The Plate Boundary Observatory (PBO), a system of GPS arrays and
strainmeters64 that measure the active boundary zone between the Pacific and
North American tectonic plates in the western United States; and
• USArray, 400 transportable seismometers that will be deployed systematically
across the United States on a uniform grid to provide a complete image of North
America from continuous seismic measurements.
SAFOD and PBO are in place and providing data to the seismological community. USArray is
progressing across North America and is also furnishing real-time data to seismologists. The
portable array currently covers the midsection of the United States and is moving east. The
installation plan calls for completing the portable array by 2013.65
62 See http://www.nsf.gov/div/index.jsp?div=EAR.
63 See http://www.earthscope.org/.
64 A strainmeter is a tool used by seismologists to measure the motion of one point relative to another.
65 See http://www.usarray.org/maps.
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Network for Earthquake Engineering Simulation
Through its Engineering Directorate, NSF funds the George E. Brown Jr. Network for Earthquake
Engineering Simulation (NEES), a project intended to operate until 2014, aimed at understanding
the effects of earthquakes on structures and materials.66 To achieve the program’s goal, the NEES
facilities conduct experiments and computer simulations of how buildings, bridges, utilities,
coastal regions, and materials behave during an earthquake. In the first six years of operations
since 2004, 160 multiyear projects have been completed or are in progress under NEES.67
Conclusion
At present earthquakes can be neither accurately predicted nor prevented, and in its 1990
reauthorization NEHRP shifted its program emphasis from prediction to hazard reduction. The
program’s focus has been on understanding the earthquake hazard and its risk to populations and
infrastructure in the United States, developing effective measures to reduce earthquake hazards,
and promoting the adoption of earthquake hazards reduction measures in vulnerable areas.
Legislation to modify NEHRP in the 108th Congress (P.L. 108-360) reflected congressional
concerns about how well the four NEHRP agencies coordinated their efforts to maximize the
program’s potential. If legislation is introduced in the 112th Congress to modify the program and
reauthorize appropriations, Congress may consider evaluating how effectively the agencies have
responded to Congress’s direction in P.L. 108-360 to improve coordination since 2004.
In the 111th Congress, legislation introduced to make changes to NEHRP, H.R. 3820,
reemphasized that approach but cast it in terms of hazard mitigation by stating that a major goal
for the program should be “to reduce the loss of life and damage to communities and
infrastructure through increasing the adoption of hazard mitigation measures.” The bill further
emphasized the social aspects of mitigating earthquake hazards, calling for research to better
understand institutional, social, behavioral, and economic factors that influence how risk
mitigation is implemented, in addition to the traditional research into understanding how, why,
and where earthquakes occur.
The emphasis on mitigation proposed by H.R. 3820 in the 111th Congress reflects at least two
fundamental challenges to increasing the nation’s resiliency to earthquakes, and to most other
major natural hazards such as hurricanes and major floods. The first is to assess whether social,
behavioral, and economic factors can be understood in sufficient degree to devise strategies that
influence behavior to mitigate risk posed by the hazard. Put simply, what motivates people and
communities to adopt risk mitigation measures that address the potential hazard? A second
challenge, which is more squarely an issue for Congress, is how to measure the effectiveness of
NEHRP more quantitatively. It is inherently difficult to capture precisely, in terms of dollars
saved or fatalities prevented, the effectiveness of mitigation measures taken before an earthquake
66 Management for NEES has been headquartered at Purdue University’s Discovery Park since October 1, 2009.
Institutions participating in NEES include Cornell University; Lehigh University; Oregon State University; Rensselaer
Polytechnical Institute; University of Buffalo-State University of New York; University of California-Berkeley;
University of California-Davis; University of California-Los Angeles; University of California-San Diego; University
of California-Santa Barbara; University of Colorado-Boulder; University of Illinois at Urbana-Champaign; University
of Minnesota; University of Nevada-Reno; and University of Texas at Austin. See http://www.nees.org/.
67 See http://nees.org/about.
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occurs. A major earthquake in a populated urban area within the United States would cause
damage, and a question becomes how much damage would be prevented by mitigation strategies
underpinned by the NEHRP program.
A precise relationship between earthquake mitigation measures, NEHRP and other federal
earthquake-related activities, and reduced losses from an actual earthquake may never be
possible. However, as more accurate seismic hazard maps evolve, as understanding of the
relationship between ground motion and building safety improves, and as new tools for issuing
warnings and alerts such as ShakeMap and PAGER are devised, trends denoting the effectiveness
of mitigation strategies and NEHRP activities may emerge more clearly. Without an ability to
precisely predict earthquakes, Congress is likely to face an ongoing challenge in determining the
most effective federal approach to increasing the nation’s resilience to low-probability but high-
impact natural hazards, such as major earthquakes.
Author Contact Information
Peter Folger
Specialist in Energy and Natural Resources Policy
pfolger@crs.loc.gov, 7-1517
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