"Evidence that earthquakes threaten the Mississippi, Ohio, and Wabash River valleys of the Central United States abounds. In fact, several of the largest historical earthquakes to strike the continental United States occurred in the winter of 1811--1812 along the New Madrid seismic zone, which stretches from just west of Memphis, Tenn., into southern Illinois (fig. 1). Several times in the past century, moderate earthquakes have been widely felt in the Wabash Valley seismic zone along the southern border of Illinois and Indiana (fig. 1). Throughout the region, between 150 and 200 earthquakes are recorded annually by a network of monitoring instruments, although most are too small to be felt by people. Geologic evidence for prehistoric earthquakes throughout the region has been mounting since the late 1970s. But how significant is the threat? How likely are large earthquakes and, more importantly, what is the chance that the shaking they cause will be damaging? […]The USGS produces earthquake (seismic) hazard maps on a national scale (fig. 2). Hazard maps are also now produced in select urban areas. At either scale there are a suite of maps for different probabilities and time periods; the choice of which to use depends upon the needs of the user. Builders of a dam, for instance, might want to consider longer periods of time and less likely levels of shaking than a home builder. This is because a dam is built to have a longer life, and damage to it would have a greater impact on society."
U.S. Geological Survey: http://www.usgs.gov/