Scientists from the U.S. Geological Survey (USGS) and the Center for Earthquake Research and Information at the University of Memphis have updated their expectations for earthquakes in the New Madrid Seismic Zone.
The new forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811-1812, which likely had magnitudes of between 7.5 and 8.0.
There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6.0 or greater earthquake.
The earthquake probabilities in this region have changed considerably since the most commonly cited forecast published in 1985. The new probabilities show an increased chance of larger (7.5-8.0 magnitude) earthquakes and a lesser chance of magnitude 6.0 and greater earthquakes. Meanwhile, estimates of the hazard, or potential for damage caused by shaking, have changed much less. A fact sheet with the new information is available on the web at: http://pubs.usgs.gov/fs/fs-131-02/.
"More than fifteen years of research has given us the information to allow us to update our forecasts. But even though the chances of a mid-sized earthquake are reduced, the chances of a devastating earthquake in the region have risen," said USGS scientist Eugene Schweig. "Given this new information, people should absolutely not drop their guard. The threat of an earthquake to Mid-America is still very real."
The New Madrid seismic zone is an area of frequent small earthquakes that stretches along the lower Mississippi Valley from just west of Memphis, Tennessee into southern Illinois. It also was the location of a sequence of three or four major earthquakes in 1811 and 1812.
Major earthquakes in the range of magnitude 7.5 to 8.0 are capable of causing widespread damage over a large region. Magnitude 6.0 earthquakes can cause serious damage in areas close to the earthquake?s epicenter because the hazard (chance of damage in a given area) depends not only on earthquake size, but also on where the earthquakes occur and local soil conditions.
In Memphis and throughout the Mid-America region, the USGS is improving its earthquake monitoring and reporting capabilities through the Advanced National Seismic System (ANSS), a nation-wide network of modern strong motion seismometers that can provide emergency-response personnel with real-time "shaking" information within minutes of an earthquake.
ANSS stations assist emergency responders within minutes of an event showing not only the magnitude and epicenter, but where damage is most likely to have occurred.
Ten new ANSS instruments were recently installed in the Memphis area, 20 have been installed across the mid-America region, and more than 175 have been installed in other vulnerable urban areas outside the central U.S. to provide real-time information on how the ground responds when a strong earthquake happens.
"The ultimate goal of ANSS is to save lives and ensure public safety," said Dr. John Filson, USGS Earthquake Program Coordinator. "This information, already available in Southern California, is generated by data from seismic instruments installed in urban areas and has revolutionized the response time of emergency managers to an earthquake, but its success depends on further deployment of instruments in other vulnerable cities."
In 1997, during the reauthorization of the National Earthquake Hazards Reduction Program, Congress asked for an assessment of the status and needs of earthquake monitoring. The result was the authorization of ANSS to be implemented by the USGS. The system, when fully implemented, would integrate all regional and national networks with 7,000 new seismic instruments, including 6,000 new strong-motion sensors in 26 at-risk urban areas. To date, approximately 350 instruments have been installed nationwide.
New USGS National Seismic Hazard Maps depict these hazard or likelihood of ground shaking. The USGS and its partners in universities and state geological surveys are preparing more detailed hazard maps for Memphis and other areas that include the effects of local soil conditions. For more information see http://geohazards.cr.usgs.gov/eq/.
The goal of USGS earthquake monitoring is to mitigate risk - using better instruments to understand the damage shaking causes and to provide information to help engineers create stronger and sounder structures that ensure vital infrastructures, utility, water, and communication networks keep operating safely and efficiently.