USGS Updates Seismic Hazard Maps, Ground Shaking Estimates
Last week's magnitude-5.2 earthquake in southern Illinois is a reminder that earthquakes are a national hazard, says the U.S. Geological Survey, which earlier this week released an updated version of its National Seismic Hazard Maps, available at http://earthquake.usgs.gov/research/hazmaps/. Earthquakes remain a serious threat in 46 of the United States, USGS scientists say. For some areas such as western Oregon and Washington, the new maps contain higher estimates for how hard the ground will shake compared to earlier versions of the maps released in 1996 and 2002. But for most of the United States, the ground shaking estimates are lower.
The revised maps incorporate new seismic, geologic, and geodetic information on earthquake rates and the manner in which the energy released in earthquakes dies off with distance from the rupture. Such data provide information essential to creating and updating the seismic design provisions of building codes used in the United States, and the timing of the updated maps' release is tied to the schedule for revising model building codes that are developed by international code committees and then considered by state and local governments for adoption. Cities and counties rely on seismic design provisions in building codes to ensure that structures such as buildings, bridges, highways and utilities are earthquake resistant.
Other applications of the revisions, which consist of a series of maps and databases describing ground shaking at many points across the country, include use by insurance companies to set insurance rates for properties in various areas of the country, by civil engineers to estimate the stability and landslide potential of hillsides, by the U.S. EPA to set construction standards that ensure the safety of waste-disposal facilities, and by FEMA to plan the allocation of assistance funds for earthquake education and preparedness.
The geologic and geophysical data-collection, research and modeling results that underpin the maps have been generated by USGS scientists as well as their colleagues in academia, state government, and the private sector funded by external grants from the USGS Earthquake Hazards Program and other sources. The new maps represent the best available science as determined by the USGS based on an extensive information gathering and review process involving state and university experts nationwide. USGS encourages all citizens in earthquake-prone areas to follow the Seven Steps to Earthquake Safety, which can be accessed at www.earthquakecountry.info/roots/seven_steps.html.