U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 183-96

Revised July 2001

Hazard Maps Help Save Lives and Property

REDUCING EARTHQUAKE LOSSES THROUGHOUT THE UNITED STATES

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America’s first line of defense against

earthquakes has historically been the construction of buildings that can withstand severe shaking. Cities and counties rely on the

seismic design provisions in building codes

to ensure that structures can resist earthquakes. The variations in the seismic threat

across the country are depicted on special

maps in building codes, called design maps,

as zones or contours of different recommended levels of design for earthquake-resistant construction. These design maps are

based on shaking-hazard maps prepared by

U.S. Geological Survey (USGS) scientists

and engineers as part of the National Earthquake Hazard Reduction Program (NEHRP).

National maps of the earthquake shaking

hazard in the United States have been produced since 1948. Scientists revise these

maps as new earthquake studies improve

ational maps of earthquake

shaking hazards provide

information essential to creating

and updating the seismic design

provisions of building codes used

in the United States. Scientists

frequently revise these maps to

reflect new knowledge. Buildings, bridges, highways, and

utilities built to meet modern

seismic design provisions are

better able to withstand earthquakes, not only saving lives but

also enabling critical activities to

continue with less disruption.

their understanding of this hazard. After

thorough review, professional organizations

of engineers in turn update the seismic design maps and seismic design provisions

contained in building codes. More than

20,000 cities, counties, and local government

agencies use building codes, such as the Uniform Building Code, to help establish the

construction requirements necessary to preserve public health and safety in earthquakes.

Shaking-hazard maps have many other

applications. For example, the 1976 U.S.

Geological Survey (USGS) shaking-hazard

map for the United States was used for

many years as the basis of design requirements for highway bridges nationwide.

Such maps are also used by:

• Insurance companies to set insurance

rates for properties in various areas of the

country,

• Civil engineers to estimate the stability

and landslide potential of hillsides,

• The Environmental Protection Agency to

set construction standards that help ensure the safety of waste-disposal facilities, and

• The Federal Emergency Management

Agency (FEMA) to plan the allocation of

assistance funds for earthquake education

and preparedness.

A new series of national shaking-hazard

maps was prepared by the USGS in 1996.

Each of these maps shows the severity of

expected earthquake shaking for a particular

level of probability. For example, the map

at the top of this page shows levels of earthquake shaking that have a 1-in-10 chance

of being exceeded in a 50-year period. This

new series of maps also depicts shaking

using a number of different measures that

engineers can readily apply to designing

earthquake-resistant buildings of

different heights.

Highest hazard

Lowest hazard

24–32

32 +

16–24

8–16

4–8

2–4

0–2

% g

The 1996 U.S. Geological Survey shaking-hazard maps for the United States are based on current information

about the rate at which earthquakes occur in different areas and on how far strong shaking extends from

quake sources. Colors on this particular map show the levels of horizontal shaking that have a 1-in-10 chance

of being exceeded in a 50-year period. Shaking is expressed as a percentage of g (g is the acceleration of a

falling object due to gravity).

The upper wall of this unreinforced

masonry building in Fillmore,

California, collapsed and destroyed a

parked vehicle during the 1994

Northridge earthquake. Unreinforced

masonry buildings are especially

susceptible to collapse or severe

damage during strong earthquake

shaking. Shaking-hazard maps can be

used to determine if such buildings in

a particular area need to be reinforced

to make them safe in earthquakes.
For more information contact:

Earthquake Information Hotline (650) 329-4085

U.S. Geological Survey, Mail Stop 977

345 Middlefield Road, Menlo Park, CA 94025

http://quake.wr.usgs.gov

Shaking-hazard maps prepared by U.S. Geological Survey (USGS) scientists are used by professional organizations of engineers to improve the seismic-zone maps

published in building codes, such as the Uniform BuildThis home in Santa Cruz, California, damaged in the

1989 Loma Prieta earthquake, shows the effects of a

weak “cripple-wall” connection between the upper

part of the house and its foundation. Houses without

adequate connections to foundations can easily shift

during even moderate earthquake shaking, causing

extensive damage. For example, pipes and wires may

be broken by a slight cripple-wall shift, resulting in

fires, water damage, or other problems. Much damage

of this type can be avoided by using inexpensive

bracing techniques, such as those recommended in

the seismic design provisions of building codes.

COOPERATING AGENCIES

American Assoc. of State Hwy. Transportation Officials

American National Standards Institute

American Society of Civil Engineers

Applied Technology Council

Building Officials and Code Administrators International

Building Seismic Safety Council

California Division of Mines and Geology

Environmental Protection Agency

Federal Emergency Management Agency

International Conference of Building Officials

National Center for Earthquake Engineering Research

National Oceanic and Atmospheric Administration

Southern Building Code Congress

Southern California Earthquake Center

Structural Engineers Association of California

William M. Brown III, David M. Perkins,

Edgar V. Leyendecker, Arthur D. Frankel,

James W. Hendley II, and Peter H. Stauffer

Graphic design by

Sara Boore and Susan Mayfield

ing Code (UBC). The 1976 USGS shaking-hazard map represented a substantially improved understanding of the

earthquake hazard nationwide and was used to produce

the updated 1988 UBC seismic-zone map, which added

zone 4 to represent a newly recognized higher level of hazard. Contours from 1996 USGS hazard maps are used in the

1997 map from the “NEHRP Recommended Provisions” published by the Building Seismic Safety Council (BSSC).

Shaking-hazard maps can be combined

with data about the strength of existing

buildings to estimate expected earthquake

damage in an area over a given period of

time. Although strong earthquakes are less

frequent in the Central and Eastern United

States than in California, damage in those

regions could be catastrophic in a powerful

temblor. This is because most buildings and

other structures there have not been constructed to withstand severe earthquake

shaking. For example, the shaking hazard in

Boston is far lower than that in Los Angeles,

but a strong earthquake striking the Boston

area today could produce much greater

damage to structures than one striking Los

Angeles. A single earthquake in the Central

or Eastern United States could cause as

many casualties and as much damage as

several earthquakes of similar magnitude

in California.

To familiarize design engineers, local

public officials, emergency-services personnel, and other users with shaking-hazard

maps and earthquake risk issues, the USGS

conducts workshops throughout the country.

These seminars have, for example, been

held in New York, Memphis, Salt Lake City,

San Francisco, and Seattle, and will continue in these and other places in the future.

As new maps are prepared, the latest shaking-hazard maps will also be available for

examination and comment on the Internet at

http://geohazards.cr.usgs.gov/eq/index.html.

Recently, the USGS worked with the

FEMA-funded Building Seismic Safety

Council (BSSC) to produce new seismic design maps for the United States, based on

the 1996 USGS shaking-hazard maps. The

new design maps were published by the

BSSC in its 1997 and 2000 “NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures.” These maps have been included in

the seismic provisions of U.S. model building codes, such as the new “International

Building Code,” and in national standards

such as “Minimum Design Loads for Buildings and Other Structures,” prepared by the

American Society of Structural Engineers.

Through the continuing process of refining estimates of the earthquake-shaking hazard across the Nation and observing successes and failures in building design,

scientists and engineers are laying the

groundwork for future urban environments

that will be safer in earthquakes. By improving the resistance of homes, office

buildings, hospitals, highways, dams, and

utilities to earthquake shaking, scientists

and engineers also help to ensure that communities are able to recover rapidly following a major temblor.

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1970 UBC hazard zones 1976 USGS shaking-hazard map 1988 UBC hazard zones

Contours show values of shaking that have a 

1-in-10 chance of being exceeded during 

earthquakes in a 50-year period. The values 

are expressed as a percentage of g (g is the 

acceleration of a falling object due to gravity).

Contours show levels of horizontal response 

acceleration (as a percentage of g), for a 

building of 1-second natural period, that have 

a 1-in-50 chance of being exceeded during 

earthquakes in a 50-year period.

Design map from 1997 NEHRP 

Recommended Provisions