Frequently Asked Questions
Natural Hazards
The USGS monitors and conducts research on a wide range of natural hazards to help decision-makers prepare for and respond to hazard events that threaten life and property.
Not really. The USGS Seismic Hazard Maps website and the Unified Hazard Tool (for building custom maps) are designed to display the probability of different events that might occur in a several-year to several-decade period. The model bases all probability estimates on the average rate of earthquakes over long periods of time.
As you shorten the...
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...
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;...
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...
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 in the United States over a certain time period. The calculation is based on the latest available information from seismic hazard data.
However, asking if it's safe...
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...
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...
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...
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 (...
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-...
Although you may hear the terms “seismic zone” and “seismic hazard zone” used interchangeably, they really describe two slightly different things. A seismic zone is used to describe an area where earthquakes tend to focus; for example, the New Madrid Seismic Zone in the Central United States. A seismic hazard zone describes an area with a...
Beginning in 2009, Oklahoma experienced a surge in seismicity. This surge was so large that its rate of magnitude 3 and larger earthquakes exceeded California’s from 2014 through 2017.
Bar graph showing the number of M3+ Earthquakes in Oklahoma vs California from 1990 to 2019. California earthquake counts are shown as a blue bar and Oklahoma...