2009 National Earthquake Hazards Reduction Program: Ground Motion Site Effects in the Wabash Valley Region from the 18 April 2008 Mt Carmel Illinois Earthquake and Aftershocks

The M5.2 Mt. Cannel, ll1inois earthquake of 18 April 2008 and three moderate aftershocks have triggered several IO's of blast monitors in Indiana, ll1inois, and Kentucky. The resulting free-field records provide a unique opportunity to further assess the reliability of current NEHRP provisions for seismic hazard amplification in this area of the central United States. Specifically, we plan to organize and process the data, derive basic ground motion parameters (e.g. peak particle velocity, peak particle acceleration, 5% damped spectral accelerations, etc.,), perfonn high-resolution dynamic site investigations at accessible sites to determine the role of site effects on the sequence of ground motions, and examine the possible role of the thin layers of low S-wave velocity bedrock in the area on higher (>2 Hz) ground motions. In addition, the results will be evaluated and compared with our previous studies that used equivalent data from the June 10, 1987, Olney, ll1inois earthquake, the June 18,2002, Dannstadt, Indiana earthquake, and two unpublished data sets of smaller events that occurred in 2002 and 2003 in southwestern ll1inois near the epicenters of the April 2008 sequence. Resultant analyses of the particle velocity time histories will provide significant insight of the regional ground motion (i.e., ground motion propagation, site effects in southern Indiana and ll1inois, and north central Kentucky, and the S- and P-wave velocity structures for the soil overburden and underlying bedrock). )