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:
- Past faults and earthquakes
- The behavior of seismic waves as they travel through different parts of the U.S. crust
- 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.
What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?
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?
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.
New seismic hazard and risk assessments can help at-risk communities prepare for future earthquake disasters
New Audiences, New Products for the National Seismic Hazard Maps
Friday's magnitude-5.2 earthquake in southern Illinois is a reminder that earthquakes are a national hazard.
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.
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.
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...
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.
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...