UNDERSTANDING EARTHQUAKE HAZARDS IN URBAN AREAS

I

mmediately following an earthquake, emergency managers must make quick response decisions using limited information. Automatically and rapidly generated computer maps of the intensity of ground shaking (ShakeMaps) are now 

available for California within about 10 minutes of an earthquake. This quick, accurate, and important information can aid 

in making the most effective use of emergency-response resources.

If only they had been available. . . ShakeMaps did not exist in 1994 when the magnitude 6.7 

Northridge, Calif., earthquake occurred. Had a ShakeMap been available for that earthquake, it could have 

been used to rapidly guide emergency-response teams to areas that potentially had the greatest need. The 

above ShakeMap is made with data recorded from the Northridge earthquake. It shows that the greatest 

shaking occurred to the north of the epicenter and in other isolated areas, a pattern that could not have 

been anticipated with only magnitude and location information for the earthquake.

ShakeMap is a tool used to portray the extent of potentially damaging shaking following an earthquake. 

It can be found on the Internet at 

http://earthquake.usgs.gov/shakemap/

and is automatically generated for 

both small and large earthquakes in 

areas where it is available. It can be 

used for emergency response, loss 

estimation, and public information. 

ShakeMap was first developed for 

earthquakes in southern California 

as part of the TriNet Project, a 

joint effort by the U.S. Geological 

Survey (USGS), California Institute 

of Technology (Caltech), and the 

California Geological Survey (CGS).

Following the Northridge 

earthquake in 1994, older analog 

instruments were replaced with a 

state-of-the-art seismic network with 

digital communications in real time. 

Deployment was completed in 2002. 

This network enables seismic data 

to be used in new and innovative 

ways. A product of the new network, 

ShakeMap, was made possible by 

advances in telecommunications 

and computer-processing speed, and 

research aimed at understanding the 

relation between recorded ground 

motions and damage intensities. 

ShakeMaps show the distribution of 

What is ShakeMap?

ground shaking in the region, inforby the earthquake), that provides use- Why ShakeMap is Necessary mation critical for emergencymanagement decision-making. It is ful information about areas prone to After a damaging earthquake,

the distribution of intensity (local damage. Having this information in emergency managers must quickly

severity of shaking), rather than the real time will result in lives saved and find answers to important questions:

magnitude (the total energy released reductions in property damage. Where is the most serious damage? 

U.S. Department of the Interior USGS Fact Sheet FS-087-03

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ShakeMap—

A Tool for Earthquake Response
Making ShakeMap

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1 The shaking level is 

recorded at hundreds 

of seismic stations 

(triangles). In the areas 

between stations, shaking 

levels are estimated on 

the basis of knowledge 

of how seismic energy 

travels and of the local 

geology. Relatively weak 

soils that transmit seismic 

energy more easily are 

shown in orange, yellow, and red. Stronger units are 

shown in green and blue.

2 Example from 

the 1999 Hector 

Mine, Calif., earthquake. Groundmotion amplitudes 

are contoured to 

indicate where 

recorded motions 

were strongest. 

Here, topography is 

color coded (browns 

and yellows 

indicate higher 

elevation, blues 

and greens indicate 

lower elevation).

3 Ground motions are converted to color-coded seismic intensity to 

show potential damage and perceived shaking level at all locations. 

Additional maps provide information on specific frequencies of 

shaking waves, that can be used to anticipate the response of different types of buildings to the ground motion. These are useful for 

estimating which areas are most likely to have damaged buildings 

and utility and transportation lifelines. All the maps are refined and 

updated as more data become available.

ANZA

BAKER

BARSTOW

BLYTHE

DESERT CENTER IRVINE

L.ISABELLA

LITTLE LAKE

LONG BEACH

LOS ANGELES

MOJAVE

NEEDLES

PALM SPRINGS

PALMDALE

S

RIVERSIDE

SAN BERNARDINO

SHOSHONE

TEMECULA

TRONA

TWENTYNINE PALMS

0 20 40 60

km

-118� -117� -116� -115�

34�

35�

36�

Where is less damage? What resources must be mobilized and in what 

quantities? Government response 

organizations typically answer these 

questions after a preliminary survey 

of the damaged area. Private-sector 

organizations conduct their own 

investigations but also wait for government reports regarding damage. 

This reconnaissance requires hours 

and sometimes days to complete. As 

a result, decisions regarding search 

and rescue, medical emergency 

response, care and shelter for the 

injured and displaced persons, and 

other critical response needs must 

often be made while information is 

still incomplete.

In the past, rapidly available information on an earthquake 

included the magnitude, location,

and some assessment of the probability of damaging aftershocks. Even

though useful, this information was 

not sufficient to support rapid postShakeMap s rapid portrayal of 

shaking distribution following an 

earthquake provides opportunities 

to enhance post-disaster response 

by integrating other useful technologies including geographic information systems (GIS) and the Federal 

Emergency Management Agencyʼs 

(FEMA) loss-estimation software 

(HAZUS). City, county, and State 

agencies can obtain ShakeMap 

“shapefiles” for use as overlays with 

GIS, providing a more detailed understanding of potential damage to local 

infrastructure and facilitating a more 

effective response. HAZUS estimates 

economic (damage and dollar losses) 

and societal impacts (number of 

casualties, displaced families, shelter 

needs) of earthquakes. The California 

Office of Emergency Services uses 

ShakeMap rather than magnitude and 

location to calculate HAZUS loss estimates, thus generating estimates based 

on actual measured ground shaking. 

earthquake emergency-management 

decision-making. Because an earthquake happens over a fault surface, 

not at a single point, the location of 

the earthquake (the epicenter) tells us 

only where the earthquake started, not 

necessarily where the shaking was the 

greatest. For a large earthquake, damage can sometimes occur hundreds 

of miles from the epicenter. Other 

factors, such as rupture direction and 

local geology, influence the amount of 

shaking in a particular area.

Although emergency responders identified many areas of heavy 

damage soon after both the 1994 

Northridge and the 1989 Loma Prieta 

earthquakes in California, additional 

regions of severe damage were only 

belatedly discovered. A ShakeMap 

displays the distribution of ground 

shaking within minutes after an earthquake so that emergency services may 

be deployed to those locations. 

Putting ShakeMap to Use

7

7

7

7

7

7

7

7

7

7

7

7

7

7

7

14

14

14

14

21

21 28

35

42

0 20 40 60

km
Modesto

Monterey

San Jose

San Francisco

Santa Cruz

San Juan Bautista

0 10 20 30

km

SHAKING WEAK STRONG SEVERE

TV ShakeMaps. ShakeMap for the 1989 Loma Prieta (“World Series”) earthquake with photographs indicating representative damage at specific locations on the map. As was the case for the Northridge earthquake, ShakeMap did not 

exist in 1989, but this map was created later with data recorded during the earthquake. This particular ShakeMap format 

is made specifically for television broadcast, with larger features and a simplified color legend. News organizations can 

now get these maps automatically and provide vital information to millions of viewers immediately after an earthquake.

1857 Scenario. “Scenario” ShakeMap for a hypothetical repeat of the 

magnitude 7.8, 1857 Fort Tejon earthquake in southern California. Strong, potentially 

damaging shaking occurred as far as 200 miles from the epicenter (star) over a 

significant portion of the State. The most severe shaking occurred near a portion of 

the San Andreas fault that ruptured (black trace). Color scale is the same as that of 

the Northridge ShakeMap.

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BAKERSFIELD

BANNING

BARSTOW

BIG BEAR

CASTAIC

COALINGA

SAN MIGUEL IS. SANTA CRUZ IS.

EDWARDS AFB

FORT IRWIN

GORMAN

L.ISABELLA

L.HUGHES

LITTLE LAKE

LOMPOC

LONG BEACH

MALIBULOS ANGELES

MOJAVE

NORTHRIDGE

OJAI

OLANCHA

PALMDALE

PANAMINT SPRINGS

PARKFIELD

PASADENA

L. PERRIS

POINT CONCEPTION

PORTERVILLE

RIVERSIDE

SAN BERNARDINO

SAN LUIS OBISPO

ON

SANTA MARIA

TRONA

TW

VENTURA

VICTORVILLE

VISALIA

WRIGHTWOOD

0 20 40 60

KILOMETERS

Likelihood of Damage to Schools. Scenerio map for an earthquake similar to the 

1989 magnitude 6.9 Loma Prieta, Calif., earthquake, prepared using a geographic information 

system (GIS). This map was made by using ShakeMap input for Hazards U.S. (HAZUS) lossestimation software. Probable damage to schools is just one of many HAZUS maps produced 

to help evaluate and respond rapidly following a damaging earthquake. The Federal Emergency 

Management Agency (FEMA), statewide agencies, and local municipalities also use HAZUS 

to plan their response to earthquake disasters. Figure courtesy of L. Christensen, California 

Governor’s Office of Emergency Services (OES).

Created by:

L. Christiansen CA OES GIS Unit

email: lisa.christiansen@oes.ca.gov

Probability of Extensive Damage to Schools

County Boundary

Interstate

Damage to Schools HAZUS MODEL RUN

Loma Prieta Magnitude 6.9

9/12/2002 4:44:48 AM

Response and recovery efforts by 

utilities and private companies benefit 

from quick knowledge of where facilities are likely to be damaged, and 

which employees may be unavailable 

due to the location of their homes 

or commuting routes with respect to 

damaged areas.

Using ShakeMap, the California 

Department of Transportation 

(Caltrans) will evaluate traffic flow 

and prioritize inspection of the nearly 

25,000 bridges and overpasses statewide, and earthquake engineers will 

prioritize building-safety inspections, 

an otherwise potentially overwhelming 

task. The public will also have access 

to the information needed to understand their situation, or to gauge the 

severity of the shaking in communities 

where relatives reside. 

ShakeMaps are organized in a database and made available on the World 

Wide Web. The maps are interactive—

selection of an individual station on 

the map displays detailed information, 

including the station name, geographic 

coordinates, and the local peak groundmotion values. The Web site provides 

access not only to maps of the most 

recent earthquakes but also to maps of 

significant events in the past and shaking expected for candidate earthquake 

ruptures in the future—so called 

“scenario” earthquakes.
Northridge (M 6.7) versus Nisqually (M 6.8)

these displays.

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Comparison of ShakeMaps generated for the magnitude

6.7, 1994 Northridge, Calif., and the magnitude 6.8, 2001

Nisqually, Wash., earthquakes. Though similar in magnitude,

the difference in earthquake focal depth resulted in substantially diffe

Northridge

rent levels of shaking and damage and, therefore,

necessitated very different levels of emergency response.

Such differences are not obvious from the magnitude and

epicenter information alone but are readily discernable from

Depth Range ~3 to 11 mi

Nisqually

Juan de Fuca Plate Depth Range ~30 to 36 mi

Magnitude Scale

Magnitude is a number representing

the total amount of energy released by

the earthquake source. It is based on

the amplitude of the earthquake waves

recorded on instruments that have a

common calibration. The magnitude of

an earthquake is thus represented by a

single, instrumentally determined value.

Modified Mercalli Intensity Scale

Intensity describes the effects of ground

shaking on people, buildings, and natural

features. It varies from place to place within the affected region, depending on the

location of the observer with respect to the

earthquake epicenter. In general, the intensity decreases as one moves away from

the fault, but other factors such as rupture

direction and local geology also influence

the amount of shaking. Roman numerals

are commonly used to describe intensities

to distinguish them from magnitudes. The

Modified Mercalli Intensity Scale is currently used in the United States and ranges

from I to X.

Despite the similar magnitudes, the shaking intensity of the Northridge earthquake reached IX (very strong)

close to the epicenter (note the red shading near Northridge), but only reached VII for the deeper Nisqually event

(note the lack of red shading).

The Future of ShakeMaps

Current work will soon enable 

users to have automatic delivery of 

a wide range of ShakeMap products

with a variety of types of telemetry, 

including wireless devices. Coupling

automatic 

instant analysis of the users faciliShakeMap delivery with 

ties will allow immediate impact 

assessments, enabling rapid response

decisions to be made more easily and 

confidently.

Efforts are now underway to 

expand the use of ShakeMaps to 

other seismically active areas of the 

United 

the U.S. Geological Survey s

States under the auspices of 

Advanced National Seismic System

(ANSS, http://earthquake.usgs.gov/).

In addition to California, ShakeMaps 

are now being produced in other seismically active urban areas, including

Seattle and Salt Lake City. With

expanded seismic instrumentation, it

will eventually be possible for any

seismic network to generate groundshaking maps for its region and make

them rapidly available on the Internet

and through the media. An investment in high-quality instrumentation and ongoing support can result

in a system that will promote more

efficient emergency response, help

reduce losses, and save lives after

an earthquake. The work of U.S.

Geological Survey scientists within

ANSS is only part of the ongoing

USGS effort to safeguard lives and

property from future earthquakes.

For More Information Contact:

Earthquake Hazards Program

U.S. Geological Survey

Golden, CO 80401

ShakeMaps are at:

http://earthquake.usgs.gov/shakemap/

Partners: Cooperating Regional Networks 

under the Advanced National Seismic System 

(ANSS), including the California Integrated 

Seismic Network (CISN), the University of Utah 

Seismographic Stations (UUSS), and the Pacific 

Northwest Seismic Network (PNSN).

Written by David Wald, Lisa Wald, 

Bruce Worden, and Jim Goltz

Graphics and layout design by Lisa Wald and 

Eleanor M. Omdahl

This Fact Sheet is available online at 

http://pubs.usgs.gov/fs/fs-087-03/