What is seismic hazard? What is a seismic hazard map and how are they used?
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.
Learn more:
- Earthquake Hazards 101: The Basics provides more details on all of these questions.
- Unified Hazard Tool - For advanced users: earthquake hazard and probability maps, hazard curves, and deaggregation
Related
What is the probability that an earthquake is a foreshock to a larger earthquake? What is the probability that an earthquake is a foreshock to a larger earthquake?
Around the world, the likelihood that an earthquake will be followed by a larger earthquake nearby and within a week is about 5%. When an earthquake occurs, it can trigger other earthquakes nearby in what seismologists call an earthquake sequence. In most sequences, these later earthquakes will be smaller than the first one. The first, largest earthquake is called the mainshock and the later...
What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area? What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?
According to information supplied in the Uniform California Earthquake Rupture Forecast 3: 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...
What is the difference between earthquake early warning, earthquake forecasts, earthquake probabilities, and earthquake prediction? What is the difference between earthquake early warning, earthquake forecasts, earthquake probabilities, and earthquake prediction?
The USGS uses these four terms to refer to four different things. Early warning is a notification that is issued after an earthquake starts. Probabilities and forecasts are comparable to climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes. Here are more detailed descriptions of each...
Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future? Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future?
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 time window, you should expect greater and greater...
How do I get earthquake hazard maps for locations outside of the U.S.? How do I get earthquake hazard maps for locations outside of the U.S.?
The USGS has seismic hazard maps for the US, Alaska, Hawaii, Puerto Rico & U.S. Virgin Islands, Guam & Marianas and Samoa & Pacific Islands. In addition, we have created some other Foreign Hazard Maps for Afghanistan, Haiti, South America, Southeast Asia and the State of Gujarat, India. For more information about hazard maps for other locations outside of the U.S. visit the GEM (Global Earthquake...
How are engineers working to make roads and buildings safer? How are engineers working to make roads and buildings safer?
Earthquake engineers are working to make roads and buildings safer in the event of 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 funding research and development for the purpose of...
Related
What is the probability that an earthquake is a foreshock to a larger earthquake? What is the probability that an earthquake is a foreshock to a larger earthquake?
Around the world, the likelihood that an earthquake will be followed by a larger earthquake nearby and within a week is about 5%. When an earthquake occurs, it can trigger other earthquakes nearby in what seismologists call an earthquake sequence. In most sequences, these later earthquakes will be smaller than the first one. The first, largest earthquake is called the mainshock and the later...
What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area? What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?
According to information supplied in the Uniform California Earthquake Rupture Forecast 3: 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...
What is the difference between earthquake early warning, earthquake forecasts, earthquake probabilities, and earthquake prediction? What is the difference between earthquake early warning, earthquake forecasts, earthquake probabilities, and earthquake prediction?
The USGS uses these four terms to refer to four different things. Early warning is a notification that is issued after an earthquake starts. Probabilities and forecasts are comparable to climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes. Here are more detailed descriptions of each...
Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future? Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future?
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 time window, you should expect greater and greater...
How do I get earthquake hazard maps for locations outside of the U.S.? How do I get earthquake hazard maps for locations outside of the U.S.?
The USGS has seismic hazard maps for the US, Alaska, Hawaii, Puerto Rico & U.S. Virgin Islands, Guam & Marianas and Samoa & Pacific Islands. In addition, we have created some other Foreign Hazard Maps for Afghanistan, Haiti, South America, Southeast Asia and the State of Gujarat, India. For more information about hazard maps for other locations outside of the U.S. visit the GEM (Global Earthquake...
How are engineers working to make roads and buildings safer? How are engineers working to make roads and buildings safer?
Earthquake engineers are working to make roads and buildings safer in the event of 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 funding research and development for the purpose of...