U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3017

April 2008 Printed on recycled paper

United States National Seismic Hazard Maps

T he U.S. Geological Survey’s maps of earthquake shaking 

hazards provide information 

essential to creating and updating the seismic design provisions 

of building codes and insurance 

rates used in the United States. 

Periodic revisions of these maps 

incorporate the results of new 

research. 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. These maps 

can also help people assess the 

hazard to their homes or places 

of work and can also inform 

insurance rates. The 2008 U.S. Geological Survey National Seismic 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 earthquake sources. Colors on this particular map show the levels of horizontal 

shaking that have a 2-in-100 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 National Seismic Hazard Maps are revised periodically by the USGS to include new research results on earthquake faults, crustal deformation, and earthquake ground 

shaking. The timing of the updates is designed to coincide 

with the schedule for updates of model building codes. 

During the update process, USGS solicits recommendations 

for improvements from the earth science and engineering 

communities, prepares draft maps that are vetted regionally, 

and solicits both public and expert opinion in review of the 

maps before they are finalized. Producing these maps is a key 

responsibility of the USGS in the four-agency, congressionally 

established National Earthquake Hazards Reduction Program 

(NEHRP). The NEHRP agencies work cooperatively with 

appropriate national building codes and standards organizations to ensure that the most up to date and technically sound 

earthquake engineering design technology is available for use 

around the Nation. The four agencies—Federal Emergency 

Management Agency (FEMA), National Institute of Standards 

and Technology (NIST), National Science Foundation (NSF), 

and USGS—view the implementation of building codes as 

a central purpose of this partnership and the best means to 

ensure that buildings and other structures in local communities 

are adequately protected against natural hazards.

America’s first line of defense against earthquakes is 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 the earthquakes that are probable in their region. The variations in 

the seismic threat across the country are depicted on maps in 

building codes as zones of different risk levels. These building code maps are based on more detailed maps, collectively 

known as the National Seismic Hazard Maps, prepared by the 

U.S. Geological Survey (USGS) with input from scientists 

and engineers at universities, State geological surveys, and the 

private sector.

The National Seismic Hazard Maps incorporate a wealth 

of geologic and seismologic information used to estimate the 

shaking, or ground motion, from earthquakes. In particular, the 

maps incorporate estimates of the magnitudes and locations of 

all likely earthquakes, how often these earthquakes occur, and 

the strength of ground shaking that they cause. The maps are 

time-independent, as they portray a long-term average hazard 

and are not affected by the time of the last earthquake rupture. 

This attribute makes the maps well suited for use in building 

codes, where the long-term life of a structure and its resilience 

to earthquake shaking must be considered.

% g 16-32

32-48

48-64

64+

8-16

4-8

0-4

Highest hazard

Lowest hazard
Charleston, South Carolina, Earthquake August 31, 1886. 

The worst earthquake wreck in Charleston. (USGS photo 

library). Photograph by J.K. Hillers.

Seismic hazard maps have many other applications. For 

example, the 2002 USGS National Seismic Hazard Maps are 

used as the basis of seismic design requirements for highway 

bridges nationwide. Such maps are also used by:

•	 Insurance companies to set property rates in various 

areas of the country.

•	 Federal Emergency Management Agency (FEMA) to 

plan the allocation of assistance funds for education and 

preparedness and improve risk assessments.

•	 Risk and loss modeling companies to estimate potential 

losses to a region or to a portfolio of assets. 

•	 Civil engineers to estimate the stability and landslide 

potential of hillsides, and the liquefaction potential of 

strata underlying communities.

•	 U.S. Environmental Protection Agency to set construction standards that help ensure the safety of wastedisposal facilities.

A new series of National Seismic Hazard Maps was publicly released by the USGS in 2008. Each of these maps shows 

the severity of expected earthquake shaking for a particular 

level of probability. For example, the map on the front page 

shows levels of earthquake shaking that have a 2-in-100 chance 

of being exceeded in a 50-year period. The time period of 50 

years is commonly used because it represents a typical building 

lifetime, while the 2-percent probability level is usually considered an acceptable hazard level for the building codes. 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, which respond to 

different frequencies of ground motion.

The updated National Seismic Hazard Maps incorporate 

newly published seismic, geologic, and geodetic models that 

define the best available science on earthquake rates and associated ground shaking. These ground-motion models show the 

decay in ground shaking with distance from the earthquake 

source (attenuation), and incorporate the effects of varying 

soil type and faulting style. The updated attenuation models 

incorporate many recent earthquake strong-motion records 

and generally result in lower estimates of ground shaking than 

previous models. New fault studies, geologic maps, reflection 

and refraction surveys, and geodetic strain rate models provide 

insights into earthquake sizes and recurrence rates for crustal 

and subduction sources. This information was discussed with 

working groups, State geological surveys, Federal agencies, 

and other earth-science experts from industry and academia in 

revising the input models. The new ground-motion and earthquake source models result in similar or lower predicted ground 

motion across most of the United States compared to motion 

calculated in earlier versions of the hazard maps.

Through the continuing process of refining estimates of the 

shaking and earthquake hazard across the Nation and observing successes and failures in building design, scientists and 

There is no single mandatory national building code or standard for designing and constructing buildings and other structures 

in the United States. Building codes are adopted and enforced 

by individual States and by local jurisdictions within the States. 

State or local building codes are usually based on a “model” 

building code or other voluntary consensus standards. State and 

local governments may either directly adopt the model code or 

adopt the code with amendments. Today, the model building code 

that is predominantly adopted in the United States is the International Building Code (IBC), promulgated by the International 

Code Council (ICC), a non-governmental organization. The 

ICC also promulgates other model codes that impact the building 

process, such as the International Residential Code (IRC). Some 

localities have also adopted the National Fire Protection Association (NFPA) 5000 Building Construction and Safety Code.

The IBC and its companion ICC documents form the basis 

of the building codes in 46 States and have been adopted by local 

governments within the remaining 4 States; thus, State and local 

building codes adopted throughout the United States share a 

common origin. As States and localities have based their codes 

upon the model codes, the performance of buildings constructed 

in accordance with the newer building codes has improved.

The four-agency National Earthquake Hazards Reduction Program (NEHRP) supports the development of seismic 

provisions in building codes by maintaining the quality of four 

documents that build on one another:

engineers are laying the groundwork for communities to remain 

safer during future earthquakes. By improving the resilience 

to earthquake shaking of homes, office buildings, hospitals, 

highways, dams, and utilities, scientists and engineers also help 

to ensure that those communities are able to recover rapidly 

following a major temblor.

Building the Model Building Codes: The Role of

Seismic Hazard Maps
Implementation:

Built Environment

End Users:

Homeowners,

Government

Agencies, Builders,

Architects,

Engineers

State and Local

Building Codes and

Enforcement

State and Local

Governments

National Model

Building Codes,

Standards and

Guidelines

Private Sector

Entities, Professional

Societies

Earthquake Hazard

Assessments

USGS

Earth Science Research 

NSF, USGS, State

Geological Surveys,

Private Sector

Seismic Design Maps

USGS, FEMA

NEHRP

Recommended Provisions

and Design Guidance

FEMA

Basic Engineering

Research

NSF

Problem-Focused

Engineering Research

NIST

Research

Implementation

NEHRP Impact on the Built Environment

Flow chart of the Building Code Process. USGS provides both basic research and hazard information that is critical to development of seismic 

provisions in building codes. USGS works with other NEHRP agencies (FEMA, NIST, NSF) to ensure the most up to date and technically sound 

earthquake engineering design technology is available for use around the Nation.

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

State Geological Surveys

California Earthquake Authority

Environmental Protection Agency

Federal Emergency Management Agency

International Conference of Building Officials

Mid-America Earthquake Center

National Science Foundation

National Center for Earthquake Engineering Research

National Institute of Standards and Technology

National Oceanic and Atmospheric Administration

Pacific Earthquake Engineering Research Center

Southern Building Code Congress

Southern California Earthquake Center

Structural Engineers Association of California

Western States Seismic Policy Council

•	 The NEHRP Recommended Provision for Seismic 

Regulations for New Buildings and Other Structures. 

This document presents the state of the art of earthquake engineering research and practice in a form 

usable by the engineering community, and provides a 

nationally applicable resource document for all model 

codes and standards. FEMA leads the effort to maintain this document, which since its inception in 1985 

has been updated on a 3- to 5-year recurring cycle. 

USGS directly supports the update process by providing appropriate updated seismic ground motion maps 

and soil/site condition parameters that incorporate the 

latest seismological findings. USGS also prepares 

seismic design maps based on the hazard levels and 

other modifications recommended by technical committees participating in the update process. Appropriate basic (NSF-sponsored) and applied (NIST-sponsored) engineering research results are included in the 

updates. The document also serves the needs of the 

Federal Government as a baseline for executive orders 

related to Federal building design and construction.

•	 ASCE 7. The American Society of Civil Engineers 

(ASCE) supports the development on a 5-year cycle of 

the Minimum Design Loads for Buildings and Other 

Structures, known as ASCE 7. FEMA and USGS 

work with ASCE to ensure that ASCE 7 adequately 

addresses seismic loads and design in a manner that is 

“substantially equivalent” to guidelines recommended 

by the NEHRP Recommended Provisions.

Cooperating Agencies and Organizations

•	 The International Codes and the NFPA 5000. Most State 

and local jurisdictions use the IBC and the IRC as the 

basis for their building code laws and regulations; a few 

local jurisdictions have adopted NFPA 5000. The IBC 

and NFPA 5000 adopt ASCE 7 by reference for most 

seismic design requirements, and the IRC incorporates 

NEHRP-based seismic requirements directly.
For Further Information

USGS Earthquake Hazard Assessment Products and Tools

To access these products and tools and for further information, see the Web site for the U.S. Geological Survey Earth Hazards 

Program at URL http://earthquake.usgs.gov/hazmaps/, and visit http://www.nehrp.gov or e-mail info@nehrp.gov.

You may also contact Mark Petersen: mpetersen@usgs.gov.

This Web site contains maps and 

associated input/output data and documentation for probabilistic hazard maps 

for the 48 Conterminous States, Alaska, 

Hawaii, and Puerto Rico.

U.S. National Probabilistic Ground-Motion Maps

Hazard Mapping and Analysis Tools

USGS offers a number of on-line 

Web tools that allow an individual to 

assess which sources pose the greatest 

hazard in a particular region, look up 

hazard values using latitude/longitude 

or Zip code, make customized USGS 

probabilistic hazard maps for an area 

of interest, map probability of a given 

magnitude within a certain distance from 

a site, and access computer software for 

seismic hazard analysis.

Seismic Design Values for Buildings

This Web site allows users to determine design ground motion at a site for 

various building codes, using latitude/

longitude or Zip code. In addition, one

can display and download a hazard curve 

or uniform hazard spectrum for a site.

These maps show more detailed 

probabilistic seismic hazard maps for 

urban areas that take into account nearsurface geologic conditions, sedimentary 

basin structure, and directivity effects.

Urban Probabilistic Ground-Motion Maps

Maps predict the median level 

of ground shaking from a particular 

“scenario” event. They do not take into 

account the likelihood of that scenario 

occurring, but they are helpful when 

assessing the potential impact of a particular event.

Deterministic or Scenario Ground-Motion Maps

These maps forecast the likelihood of an 

earthquake rupture occurring during an interval 

of time in the future. Time-dependent maps are 

considered research tools and are not currently 

applied in building codes.

Time-Dependent Earthquake Probability Maps

U.S. Quaternary Fault and Fold Database

This Web site contains information 

on faults and associated folds in the United 

States that are believed to be sources of 

M>6 earthquakes during the Quaternary 

(the past 1,600,000 years). Maps of these 

geologic structures are linked to detailed 

descriptions and references.

Earthquake Hazards 101

USGS provides a wealth of explanatory materials for the layperson, including 

information on concepts behind earthquake maps, the use of probability, what 

the maps mean, how they are made, and 

answers to frequently asked questions.

59%

21%

31%

7%

6%

11%

31%