a joint degree program between the
college of arts and sciences and the school of public and
environmental affairs
Kim Shoemaker
Aftershock relocations of the 2008 Mt. Carmel earthquake.
BSES Senior Research 2009
On April 18, 2008, a significant earthquake of magnitud
e 5.2 occurred along the Indiana-Illinois state border near the northern section of the Wabash Valley fault system (WVFS). In order to learn about the fault structure, the hypocenters must be precisely located. The first stage required using a digital seismic analysis program which refined the P and S arrival times. Using these refined arrival times, we generated precisely located hypocenters of each event using an earthquake locating program. Based upon the S-P arrival times and a more precise velocity model for the Wabash Valley region, the program generated the latitude, longitude, depth, and origin time of each event. Out of a total of 257 events, 177 were located. The second stage involved analyzing the P arrivals based upon computed methods of cross-correlation. This method correlated waveforms of different events based upon the location of each event per station. In the third stage, we relocated the hypocenters based on the corrected P arrivals. The preliminary results indicate an east-west orientation of hypocenters with depths ranging from 9-22 km. Since the WVFS trends north-northeast, these results may indicate conjugate faulting along the northern end of the WVFS within the crystalline basement.
