The April 18, 2008, earthquake that hit southern Illinois and shook several surrounding states provided a sharp reminder that significant quakes can happen in many parts of the country. As fresh evidence of the vulnerability in 46 states, the US Geological Survey released a set of updated national earthquake maps on April 21, 2008.
The maps have been steadily upgraded as versions have been released in 1992, 2002, and 2008. The latest version offers a number of ways to look at each state or region, with different maps for selected odds of earthquake occurrence, and for various degrees of ground acceleration. In addition, there are a number of updates on the new maps, such as several new faults in the West; revised information for South Carolina; greater estimated threats for parts of Oregon and Washington; and lower estimated threats for many other areas.