What is seismic hazard? What is a seismic hazard map? How are they made? How are they used? Why are there different maps, and which one should I use?

Seismic hazard is the hazard associated with potential earthquakes in a particular area, and a seismic hazard map shows the relative hazards in different areas. The maps are made by considering what we currently know about:

  1. Past faults and earthquakes
  2. The behavior of seismic waves as they travel through different parts of the U.S. crust
  3. The near-surface site conditions at specific locations of interest

Hazard maps can be used for land-use planning, mitigation, and emergency response. 

The different maps show different probabilities that are selected to provide an idea of the relative range of hazard across the US. The larger probabilities indicate the level of ground motion likely to cause problems in the western US. The smaller probabilities show how unlikely damaging ground motions are in many places of the eastern US. However, basically the values chosen reflect the more recent history in earthquake engineering.

How does an individual person select a map? Technical users probably have to follow predefined rules. A non-technical person may be interested in avoiding living in a location where significant shaking will cause worry, deciding on whether to carry earthquake insurance, or deciding whether to do some rehabilitation for an existing dwelling. The probability level chosen should reflect how anxious one is to avoid earthquake shaking.

Earthquake Hazards 101: The Basics provides more details on all of these questions.

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How do I get earthquake hazard maps for locations outside of the U.S.?

We know of no current "zone" designations for sites outside of the United States. For locations outside the United States for which seismic design is required for military facilities, there exists a standard based on probabilistic spectral ordinates in the manner of the International Building Code and are declared to reflect the 2015 version of...

How are engineers working to make roads and buildings safer?

Earthquake engineers are working to make roads and buildings safer in the event of a major earthquakes. This includes both improving the design of new buildings and bridges as well as strengthening older units to incorporate the latest advances in seismic and structural engineering. The Federal Emergency Management Agency plays a central role in...

What is the USGS doing to mitigate and respond to earthquake hazards?

The U.S. Geological Survey performs the following functions related to earthquake hazard mitigation: Receives, analyzes, maintains, and distributes data on earthquake activity worldwide. Satellites link our National Earthquake Information Center in Golden, Colorado to a network of seismograph stations. These stations, located throughout the world...

Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future?

Not really. This web site is designed to display the probability of different sources that might occur in a several-year to several-decade period. The model bases all probability estimates on mean rate of earthquakes over long periods. As you shorten the time window, you should expect greater and greater fluctuations in what may be observed from...

What is the probability that an earthquake is a foreshock to a larger earthquake?

Worldwide the probability that an earthquake will be followed within 3 days by a large earthquake nearby is somewhere just over 6%. In California, that probability is about 6%. This means that there is about a 94% chance that any earthquake will NOT be a foreshock. In California, about half of the biggest earthquakes were preceded by foreshocks;...

Are earthquake probabilities or forecasts the same as prediction?

No. Probabilities and forecasts are rather like climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes. Probabilities describe the long-term chances that an earthquake of a certain magnitude will happen during a time window. Most earthquake...

What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?  

Los Angeles area: Within the next 30 years the probability is: 60% that an earthquake measuring magnitude 6.7 46% that an earthquake measuring magnitude 7 31% that an earthquake measuring magnitude 7.5 will occur in the Los Angeles region. San Francisco Bay area: Within the next 30 years the probability is: 72% that an earthquake measuring...

How do I decide whether or not to get earthquake insurance?

You should consider the following factors when deciding whether or not to get earthquake insurance: proximity to active earthquake faults seismic history of the region (frequency of earthquakes) time since last earthquake building construction (type of building and foundation) architectural layout materials used quality of workmanship extent to...

How do earthquakes affect buildings?

Ground shaking is the primary cause of earthquake damage to man-made structures. Many factors influence the strength of earthquake shaking at a site including the earthquake's magnitude, the site's proximity to the fault, the local geology, and the soil type . More than 250 structures throughout the United States have been outfitted with seismic...

What is the likelihood of a large earthquake at location X?  Is it safe to go to X since they've been having a lot of earthquakes lately?

The National Seismic Hazards Mapping project provides an online web tool for determining the probability of a large earthquake within 50 kilometers (~31 miles) of a specific location over a certain time period. The calculation is based on the latest available information from seismic hazard data. Unified Hazard Tool - Earthquake Hazard and...

How will my house hold up in an earthquake? Can the USGS send someone out to evaluate my property?

Published maps will only provide generalized, uninterpreted information about specific areas. Every property consists of a unique combination of geologic and structural factors that must be considered to determine what might happen to a house during an earthquake. Therefore, an individual site study is necessary. Geologic factors include: type of...

What are the earthquake hazards/risks where I live?

Determining your risk with regard to earthquakes, or more precisely shaking from earthquakes, isn't as simple as finding the nearest fault. The chances of experiencing shaking from an earthquake and/or having property damage is dependent on many different factors. The National Hazard Maps use all available data to estimate the chances of shaking (...
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Date published: April 24, 2018

East vs West Coast Earthquakes

Why was an earthquake in Virginia felt at more than twice the distance than a similar-sized earthquake in California? The answer is one that many people may not realize. Earthquakes east of the Rocky Mountains can cause noticeable ground shaking at much farther distances than comparably-sized earthquakes in the West.

Date published: March 14, 2018

USGS Authors New Report on Seismic Hazard, Risk, and Design for South America

New seismic hazard and risk assessments can help at-risk communities prepare for future earthquake disasters

Date published: June 26, 2014

New Audiences, New Products for the National Seismic Hazard Maps

New Audiences, New Products for the National Seismic Hazard Maps

Date published: April 21, 2008

Earthquake Hazard Maps Show How the Nation Shakes with Quakes

Friday's magnitude-5.2 earthquake in southern Illinois is a reminder that earthquakes are a national hazard.

Date published: April 1, 2004

New USGS Map Highlights Central U.S. Earthquake History

A new map from the U.S. Geological Survey and the Central United States Earthquake Consortium shows that Central States, including Arkansas, Tennessee, Missouri, Kentucky and Indiana are among the most seismically active states east of the Rocky Mountains. More than 800 earthquakes are cataloged on the map that depicts the locations of earthquakes large enough to be felt, since 1699.

Date published: January 22, 2001

New USGS Map Will Improve Earthquake Hazards Assessment in the Bay Area

A new geologic map of surficial deposits in the nine-county San Francisco Bay region that can be used to evaluate earthquake hazards has been released in digital form by the U.S. Geological Survey in Menlo Park.

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HayWIred scenario earthquake map
December 31, 2018

HayWired scenario earthquake map

HayWIred scenario earthquake map.

Attribution: Natural Hazards
Shaded relief image of the Santa Rosa area showing active faults
April 14, 2016

Santa Rosa area showing active faults

Shaded relief image of the Santa Rosa area showing active faults (black lines) and the detailed rupture pattern of the Rodgers Creek Fault where it crosses central Santa Rosa (in red). The orange, bean-shaped area represents the dense, magnetic body of rock on the east side of the fault beneath Santa Rosa. This body of rock may be largely responsible for the pattern of

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Google Earth image of central Santa Rosa showing the surface trace of the Rodgers Creek Fault
April 14, 2016

Google Earth Santa Rosa fault line

Google Earth image of central Santa Rosa (dated 24 October 2009) showing the surface trace of the Rodgers Creek Fault (red lines) and the inferred location of the fault prior to this study (orange dotted line). Yellow lines on either side of the fault are the boundaries of the lidar survey.

Image: USGS To Map Hayward Fault Using Seismic Energy from Building Implosion
August 7, 2013

USGS To Map Hayward Fault Using Seismic Energy from Building Implosion

Warren Hall on California State University East Bay's Hayward campus is scheduled to be demolished Aug. 17, 2013 for seismic safety reasons. The landmark building's implosion will produce energy similar to a small earthquake that can be used to study and map the nearby Hayward Fault. In partnership with the university, U.S. Geological Survey scientists will monitor the

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Image: San Andreas Fault in SE Coachella Valley
February 1, 1986

San Andreas Fault in SE Coachella Valley

Oblique aerial view of San Andreas Fault (between white arrows) in southeastern Coachella Valley, near Red Canyon; view to the west.

 

Attribution: Natural Hazards