Earthquake Scenario Ground Motions for the Urban Area of Evansville, Indiana

Abstract

The Wabash Valley seismic zone and the New Madrid seismic zone are the closest large earthquake source zones to Evansville, Indiana. The New Madrid earthquakes of 1811–1812, more than 180 km from Evansville, produced ground motions with Modified Mercalli Intensity VII near Evansville. Liquefaction evidence has been documented less than 40 km away from Evansville resulting from two large earthquakes that occurred within the past 12,000 years in the Wabash Valley. Two earthquake scenarios are described in this paper that demonstrate the expected ground motions within the 33 by 42 km2 region around Evansville based on a repeat earthquake from each of these source regions. The simulations take into account the 1-D amplification of ground motion in the unconsolidated soil layer using a new laterally varying model of seismic velocity and bedrock depth. The objective of this work is to demonstrate to what extent the local variability in ground motions due to local site effects impacts the assessment of seismic hazard. These scenario maps are a valuable complement to the probabilistic seismic hazard maps for the same area (Haase, Nowack, Choi, and Bowling 2011) because the scenario maps illustrate the direct relationship between an earthquake source and the potential hazard. Also, the scenario ground motions can be used to calculate liquefaction hazard (Haase, Nowack, and Choi 2011). These ground motion maps, along with those for the probabilistic seismic hazard and liquefaction hazard, will be useful for evaluating the potential losses from earthquakes and can be used for planning, development, hazard mitigation, and emergency response. Two earthquake source zones near Evansville, Indiana, that are considered capable of producing an M 6.5 or greater earthquake are the New Madrid seismic zone, near New Madrid, Missouri, and the Wabash Valley seismic zone along the southern border between Illinois and Indiana. The New …