New Maps Show Most of U.S. at Higher Risk for Earthquakes

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The U.S. Geological Survey on Thursday released a new report containing updated U.S. National Seismic Hazard Maps of earthquake risk for the next five decades. The new maps show that at least a portion of 42 states in the U.S. are at risk of experiencing an earthquake and many areas are now at a higher risk than previously thought. The maps depict the predictions of geologists as to how often and where earthquakes may occur as well as how strong the tremors might be.

The maps are periodically updated as part of the National Earthquakes Hazards Reduction Program, which was formed by Congress in order to reduce the risks of death and widespread damage in areas deemed to be at a higher risk for quakes. The program is made up of the Federal Emergency Management Agency, the National Science Foundation, the National Institute of Standards and Technology and the USGS.

The states at risk encompass areas of the western half of the U.S. as well as the Southeast and Midwest. Regions of sixteen states that have experienced prior quakes of 6.0 magnitude or higher are labeled as high risk areas for seismic activity. Places labeled as having the highest risk of tremors are estimated to have a total chance of an earthquake with “very intense shaking” happening over a 50-year time period (the average life span of a building) as 2 percent. Lower risk ratings coincide with less swaying motion from gravitational force as caused by quakes.

The last time the maps were updated was in 2008. Geologists took into account all earthquakes occurring in the U.S. since then. The Northeast region is shown at a higher risk due to the 2011 Virginia quake that measured 5.8 on the Richter scale, and the risk has increased in South Carolina because the Charleston area of that state has recently experienced seismic activity. Portions of Oklahoma and Colorado were also moved into the second classification from the top for earthquake hazard. The scientists also studied the effect on the United States from the Japanese earthquake and tsunami of 2011.

In addition to the inclusion of recent seismic data, new modeling programs from the University of California, Berkeley and others have improved the accuracy of the maps. GPS records of the movement of the earth along fault lines was also incorporated into the report for the first time, giving the scientists the ability to monitor bigger areas than they could with lasers.

The data contained in the new maps will be widely used by planners and engineers as they seek to design more earthquake-resistant infrastructure and buildings, and could be used to help refine and create building standards and insurance costs. In addition, residents of areas deemed to be at risk may be prompted by the new maps to form their own emergency plans in the event of an earthquake. As part of its services, homeowners can consult the USGS to help in the decision of whether or not to  renovate their existing homes to be able to stand up to an earthquake.

Geologists also hope to keep an eye on increased risks of earthquakes due to human activities, and cited the practice of disposing wastewater from gas and oil drilling into deep wells as one such action. The current map does not include the additional quakes that occurred in Oklahoma and other states due to that practice. This year alone, Oklahoma has experienced almost 250 seismic events described as being medium-sized or less that were not taken into account for the new map, which overall raises the risk of earthquakes for approximately one-third of the U.S. and decreases risk for one-tenth.

By Jennifer Pfalz

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