$2 $4 $9

$47

$115

$0

$50

$100

$150

$200

1964 1971 1989 1994 1995

Economic Losses

from Damaging Urban Earthquakes

(in billions of dollars)

AlaskaSan FernandoLoma PrietaNorthridgeKobe, Japan

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-046-03

May 2003

Earthquake Safety and Economic Losses

Earthquakes represent the single 

largest potential cause of casualties and 

damage from a natural hazard facing 

this country. The severity of the impact 

is a direct function of the performance 

of structures during strong earthquake 

shaking. Building codes require that 

structures be built to protect against loss 

of life, but they do not generally limit the 

amount of damage that a structure will 

incur. Therefore, earthquakes can have 

large economic impacts.

Although damaging earthquakes are 

infrequent, their consequences can be 

immense. According to recent studies, a 

future major earthquake in the urbanized 

area of northern or southern California 

could exceed $200 billion in losses, cause 

several thousand deaths, and significantly 

impact the national economy. In 2001, 

the Federal Emergency Management 

Agency (FEMA) reported that estimated 

future annualized earthquake losses in 

Response organizations, utilities, and 

transportation agencies depend on rapid 

shaking-level information from ANSS 

instruments to guide their critical initial post-earthquake efforts. However, 

many urban areas do not have adequate 

instrumentation to provide the input 

data for these critical maps of earthquake shaking.

Decisive action is necessary to 

counter this trend of increasing losses; 

improved engineering design and public 

planning must be part of that action.

Printed on recycled paper

the United States will average about $4.4 

billion/year based on 1990 census figures. FEMA also noted that damages and 

losses from earthquakes have steadily 

increased. Population growth, urbanization, and expansion of the built environment all contribute to this trend. In 

addition, many existing structures are not 

earthquake resistant and have not been 

retrofitted to meet current design codes.

The effectiveness of emergency 

response also plays a crucial role in the 

losses associated with an earthquake. 

I

n light of a dramatic national 

increase in monetary losses from 

earthquakes in the last two decades, 

the Advanced National Seismic 

System (ANSS) is being designed to 

integrate, modernize, standardize, 

and expand operations of seismic 

networks in the United States. The 

ANSS will improve ground and 

structural recordings of strong 

earthquake shaking in urban areas, 

providing the data necessary to 

improve structural safety and speed 

emergency response and recovery. 

This will improve the Nation’s ability 

to respond effectively to damaging earthquakes, reduce monetary 

losses, and save lives.

ANSS–Reducing the Devastating 

Effects of Earthquakes

UNDERSTANDING EARTHQUAKE HAZARDS IN URBAN AREAS

Inflation-adjusted economic losses from magnitude 

6.7 or greater earthquakes impacting major U.S. 

urban centers during the past four decades. The 

1995 Kobe, Japan, earthquake is included for 

comparison, as it also struck an urban area with 

construction standards similar to those of the 

United States. (Photo credits clockwise from top 

right - J. Dewey, USGS; Caltrans, with permission; 

J.K. Nakata, USGS.)

1994 M6.9 Northridge, Calif.

1994 Northridge, Calif.

1989 M6.7 Loma Prieta, Calif.
Lack of Structural Recordings

• Few recordings of any high-rise, steel 

moment-frame building within 20 km of a moderate to large (M>6.5) U.S. earthquake.

• Few U.S. recordings of the response of critical 

lifelines to damaging levels of motion, such as 

the six major bridges crossing the San Francisco Bay, which are being presently retrofitted 

or rebuilt.

• Only a few records used to guide the design 

of most buildings, and these records may not be 

representative of ground shaking at a site.

• Few recordings of response of modern structures to actual damaging levels of earthquake 

loading.

Lack of Ground Shaking Recordings

• Only one set of recordings (from the 2002 

Denali, Alaska, earthquake) of any major 

(M>7.5) U.S. earthquake at locations experiencing damaging levels of ground shaking.

• Limited number of recordings of the dynamic 

response of soft soils in the U.S., yet bridges, 

buildings, pipelines, and highways are being 

built on such deposits each year.

• Few recordings of large sudden coherent 

pulses of motion that occur near a fault rupture.

Correspondence between damage and amplified ground shaking in the region surrounding the 1994 Northridge, Calif. earthquake. Circles are locations where aftershock recordings were made, and their relative 

size shows amplification of ground motion from aftershocks compared to a rock site. Red symbols indicate 

red-tagged (heavily damaged) buildings. Notice that the damage is highly localized across the San Fernando Valley and is correlated with the ground motion amplification. Damage patterns appear to be related 

to the type of shallow soils and quality of building construction. If the localized hotspots of high ground 

motion amplification had been mapped prior to the Northridge earthquake, the most vulnerable structures 

could have been selectively retrofitted to resist this enhanced ground shaking. However, to recognize 

these hot spots first requires recording ground motion at many sites in urban areas and across all classes 

of buildings to assess potential damage. It also requires acquiring records from large earthquakes, not just 

related aftershocks.

(2) how buildings respond to this ground 

motion. Currently neither characteristic is 

sufficiently well understood.

The ground response to seismic shaking can be highly variable and dependent 

on a number of factors, such as near-surface geology, proximity to active faults, 

and deeper basin structure. Earthquake 

damage is often localized where geologic 

factors combine to amplify ground shaking. Presently recordings of ground motion 

in urban areas are insufficient to adequately characterize this variability.

Not all buildings respond the same 

to seismic shaking. Response is affected 

by several factors, including irregular 

shape, use of different types of structural 

systems (such as moment frames, shear 

walls, and base isolation), asymmetrical 

loading, nonstructural elements, and the 

coupling between structure and ground. 

Currently the number of seismic instruments in buildings is insufficient to monitor representative structural types, calibrate design and retrofit standards, and set 

priorities. Because of these deficiencies in 

ground and structural monitoring, engineers 

must infer the characteristics and effects of 

shaking when they design structures.

How Will ANSS Meet the Need for 

Improved Ground Shaking Observations?

Through the Advanced National 

Seismic System, the USGS will greatly 

expand the ground- and building-based 

strong motion recordings in urban areas, 

thus providing the engineering community with the data they need to improve 

building codes and structural design 

practices. The ANSS plan calls for 3,000 

additional ground-based instruments and 

3,000 structural instruments in 26 seismically active metropolitan areas across the 

United States.

The ANSS ground-based instruments 

will be positioned to sample a range of 

different soil types, geologic and basin 

conditions, and fault proximity. In addition, ANSS instruments will be deployed 

close to major fault zones to capture large 

ground motion should faults slip during 

a major earthquake. Instrument spacing 

will average 1-2 km across urban basins. 

Many types of building designs have 

never been tested by damaging levels of 

earthquake shaking, and if they have, the 

level of shaking that produced the damage 

is not well quantified. ANSS structural 

sites will be selected so as to validate and 

calibrate building design and retrofit codes 

quakes. Structural engineers must take 

into account two fundamental characteristics of earthquake shaking: (1) how 

ground shaking propagates through the 

Earth (especially near the surface), and 

Use of Strong Motion Measurements

in Reducing Future Losses

Earthquake-resistant design is the first 

line of defense in improving structural 

safety and reducing losses from earth-

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Amplification of Ground Shaking and Damage

from the 1994 Northridge, Calif. , Earthquake
and priorities, calibrate post-earthquake 

evaluation procedures, and advance new 

methods such as performance-based design 

standards. Although placement of instruments in every building is not feasible, 

monitoring representative classes of structures in different areas can produce results 

applicable to other nearby structures with 

similar characteristics. Structural instrumentation sites will be coordinated with groundbased recordings so that the input ground 

motion to the structure can be determined. 

The data acquired from these ANSS 

ground and structure recording sites will 

greatly improve the current design standards for buildings, lifelines, and other 

structures, and possibly identify critical 

weaknesses of current structures. In addition, these studies allow for considerable 

financial savings through prioritization of 

building retrofits in areas of high ground 

motion amplification.

Seismic Monitoring and

Emergency Response

Besides facilitating the improvement 

of building codes, additional seismic 

stations are important in quantifying the 

ground shaking for emergency response. 

ShakeMap is a tool that depends on strong 

ground motion records to automatically 

and rapidly generate computer maps that 

portray the extent of potentially damaging shaking following an earthquake. 

ShakeMaps can be used for emergency 

response, loss estimations, and for public 

information through emergency response 

networks, the Internet, and the media. 

Because ShakeMap interpolates ground 

motion between seismic stations, and 

because ground motion can vary widely 

even over short distances (several kilometers), dense instrumentation is necessary for detailed predictions of damage. 

ShakeMap is currently running in Los 

Angeles, San Francisco Bay Area, Seattle, 

and Salt Lake City. More instrumentation 

is required to extend ShakeMap to other 

urban centers, such as Anchorage, Boston, 

Charleston, Las Vegas, Memphis, New 

York, Portland, Reno, Saint Louis, and 

San Diego.

Strong motion recordings on and 

near structures can also be used for rapid 

damage and building state-of-health 

assessments. User-friendly displays of 

ground motion recordings are available 

that provide a facility manager with the 

information needed to evaluate–whether 

on-site or remotely–the likelihood of damage to a facility or a portion of a facility. 

Displays of peak levels of ground motion, 

combined with color-coded alarm systems 

and the ability to review recordings from 

multiple sensors deployed throughout a 

structure, provide an immediate method 

to evaluate whether a facility is safe or 

whether further action is required. In 

addition, the same data will be relayed to 

the USGS earthquake information center 

and integrated into a regional display of 

ground motion for emergency response 

and loss estimation purposes. Thus ANSS 

instrumentation used for monitoring 

earthquake-generated ground motion and 

response of the built environment can benefit both local building managers and State 

and Federal emergency response personnel, while also providing critical data that 

engineers can use to improve long-term 

building design codes and methods.

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Contoured displays of peak ground acceleration (PGA) from the February 28, 2001, M 6.8 Nisqually earthquake across the city limits of Seattle. Panel A shows 

the results provided by ANSS strong motion instruments (triangles) in place at the time of the earthquake. Panel B includes the strong motion recordings from 

panel A plus data recorded by a temporary array of 23 instruments (+ symbol). Note the identification of an area of strong shaking (orange and 

red shading) in central Seattle that was not identified based on the ANSS recordings alone. Panel C documents the close correspondence 

between this region of strong ground shaking as defined in panel B and the area experiencing damage. Red dots represent 

structural damage and ground deformation (liquefaction, lateral spreading, settling, and landslides). In the future, if instrumentation is sufficiently dense, urban areas of concentrated damage such as this can be identified in minutes following an 

earthquake and information conveyed to emergency response through ShakeMap. 
For More Information

Contact:

USGS Geologic Hazards Team

Federal Center, P.O. Box 25046 MS 966

Denver, CO 80225

303-273-8582

ANSS Website

http://www.anss.org/

Earthquake Hazards Program Website

http://earthquake.usgs.gov/

Written by Jill McCarthy, Steve Hartzell, and 

Mark Petersen

Graphic design by John Michael, Eleanor 

Omdahl, and Lisa Wald

This fact sheet is available online at:

http://pubs.usgs.gov/fs/fs-046-03/

epicenter. The absence of higher ground motion near the epicenter, and the portrayal of localized areas of anomalously high or low ground motion marked by bull’seye contour patterns (e.g., the red high east of the epicenter), are indicative of too few stations in the area.

 An enlarged picture of recorded ground motion in the vicinity of San Jose, Calif., also includes the recordings from a temporary dense array of instruments (box) 

that has a station separation of about 1 km (view B). Much more spatial variability in ground motion is clearly evident within this dense array, where an east-westoriented band of higher ground motion is revealed. The presence of this scale of ground motion variability, with an estimated 5-km north-south by 10-km east-west 

scale, cannot be resolved by the existing ANSS instrument grid owing to insufficient spatial sampling. To resolve similar scale features across the Bay Area requires 

an ANSS station spacing of 1 or 2 km. 

 Currently the number of ANSS-quality seismic stations in the San Francisco Bay Area is insufficient to map out the variability in ground motion from earthquakes. 

Approximately 100 ANSS-quality stations exist in the region, spaced every ≈10 km or more. To achieve station spacing of every 2 km will require approximately 600 

strong motion sensors across this populated urban area. 

Conclusion

ANSS offers an important next step 

in a long-term effort to reduce earthquake 

losses through improved structural and 

ground-based earthquake strong motion 

recordings. The dangers of unsafe “underbuilding” and costly “overbuilding” for 

earthquakes can only be dealt with by the 

capture of vital information when earthquakes occur. If thorough sets of strong 

motion recordings are not obtained on 

engineered structures and in the free-field 

by the time of the next damaging earthquake, then a great opportunity to mitigate 

the effects of such natural disasters will 

be lost.

 The Gilroy earthquake of May 13, 2002, provides a vivid illustration of the density of strong 

motion instrumentation needed to reduce earthquake losses. This magnitude 4.9 earthquake 

occurred in the southern San Francisco Bay Area near the town of Gilroy. The event ended a 

post-Loma Prieta earthquake period of relative seismic quiescence in the South San Francisco 

Bay region that had been ongoing since 1989. Unlike the Loma Prieta event, this earthquake 

was recorded by dozens of newly installed ANSS instruments designed to detect strong ground 

shaking from urban earthquakes. The ground motion recorded by this array is shown in view 

A. The highest ground motion (reds and oranges) is mapped about 10 km east-northeast of the 

The Gilroy Earthquake of May 13, 2002

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The 16-story Atwood building in downtown Anchorage is the first structure to be instrumented by 

ANSS with both a multi-story strong-motion array 

and borehole sensors. The integrated network 

enables scientists and engineers to analyze 

complex soil-structure interaction problems that 

significantly impact building performance in large 

earthquakes. Installation of the new equipment will 

be completed in 2003.