April 18's early-morning earthquake that jolted the central United States is a reminder that seismic events do occur outside of what many consider "earthquake country." It is also a lesson that people feel the effects of earthquakes occurring east of the Mississippi River more widely than those in the West. USGS received reports from those feeling this earthquake from as far west as Kansas, as far north as Upper Michigan and as far south as Georgia.

"Earthquakes of comparable size are felt over greater distances in the East than those occurring in the West," said Harley Benz, a seismologist for the U.S. Geological Survey. "Earthquakes in the central U.S. are infrequent, but not unexpected."

The preliminary magnitude 5.2 earthquake occurred at 4:37 a.m., Central Daylight Time. The earthquake's center was located about 38 miles north-northwest of Evansville, Ind.,or 128 miles east of St. Louis, Mo. It occurred in an area scientists refer to as the Wabash Valley Seismic Zone. Today's event is the strongest earthquake in southern Illinois since November 1968, when a 5.4 earthquake occurred.

On Monday, April 21, USGS will be issuing its new earthquake hazard assessment maps for the entire United States. State and local governments use the information to update building codes.

USGS scientists classified the April 18 earthquake event in Illinois as "moderate." The event caused some damage and produced some aftershocks; the largest, a magnitude 4.6, occurred at 10:15 a.m., Central Daylight Time, on April 18. Of much greater concern, however, is the potential for the adjacent New Madrid seismic zone to generate severe earthquakes. During the winter of 1811-1812, a series of three very large earthquakes — the strongest earthquakes to strike the lower 48 states during historic times — devastated the area. People throughout most of the nation reported feeling these earthquakes. Occurring only a few weeks apart on Dec. 16, Jan. 13, and Feb. 7, they generated hundreds of aftershocks, some severely damaging by themselves, which continued for years.

Regional building codes incorporate a significant degree of risk from earthquakes. But many buildings constructed prior to these codes or their updates are not adequately retrofitted.

Building officials use USGS' research on ground shaking to update building codes with the most current scientific information. As new buildings replace older, more dangerous structures, death tolls from earthquakes have significantly reduced in the United States.

Did you feel this earthquake? You can report your experiences on: http://earthquake.usgs.gov/eqcenter/dyfi/

More information on this event and the history of the region is found on: http://earthquake.usgs.gov/eqcenter/recenteqsus/Quakes/us2008qza6.php

For additional information, contact Diane Noserale, USGS, at (703) 648-4333.