Louisville, the largest metropolitan area in Kentucky, is located in the north-central part of the state. During the 1811-1812 New Madrid earthquakes, strong ground shaking occurred there: Modified Mercalli intensity is estimated to have been VII, and peak ground acceleration 0.1 to 0.15 g. Poulson's American Daily Advertiser, a newspaper from Philadelphia, reported, "On Monday morning the 16th instant, this place was visited by a most alarming Earthquake . . . . We are induced to believe, the continuation was from 4 to 6 minutes, though some say it was not so long; -- about an hour afterwards, another shock was felt; and a little after sunrise, a third, which broke off several chimneys, and injured some houses otherwise." Peak ground acceleration (PGA) of about 0.1 to 0.15 g can be expected in the next 500 to 2,500 years in the Louisville metropolitan area.
Seismic hazards associated with local geology, such as ground-motion amplification, liquefaction, and earthquake-induced slope failure, can cause damage during earthquakes. The Louisville metropolitan area is underlain by thick, soft soils along the Ohio River that are prone to amplification and liquefaction. Even if the ground motion is not very strong, amplification and liquefaction of near-surface soft soils could be devastating. For example, severe damage was caused in Mexico City by ground-motion amplification of soft lake deposits underneath the city in 1985, even though the epicenter was 300 kilometers away. Amplification and liquefaction can be assessed if soil properties and the depth to the groundwater table are known. KGS is characterizing important properties such as depth to bedrock and shear-wave velocity in the Louisville area, using surface geologic, water well, geotechnical, and geophysical data. The ground-motion amplification hazard is assessed by determining the average shear-wave velocity of the top 100 feet of soil. Two steps are required to properly evaluate the liquefaction hazard. In the first step, liquefaction susceptibility criteria are applied based on depositional environments and ages; this identifies the soil units that have liquefaction potential. The next step is to further evaluate the soil units that meet the liquefaction susceptibility criteria, using soil engineering properties, depth to water table, and potential for ground motion. Maps can be made that show amplification and liquefaction risk, and they can be used by emergency managers, planners, and the general public for seismic-hazard mitigation. The maps will be used to assess seismic risk for the Louisville metropolitan area using HAZUS99, a software for seismic risk evaluation developed by the Federal Emergency Management Agency.