Lg-WAVE ATTENUATION ACROSS OHIO

Seismograms for 14 regional earthquakes were analyzed to determine the effective seismic amplitude attenuation with distance across Ohio. Lg-wave amplitudes were obtained from up to 20 Ohio Seismic Network stations, which record vertical motion with a sampling of 10 Hz over a 0.05-1.5 Hz band. The events studied had mbLg magnitudes that ranged from 2.0 to 5.0 with epicentral distances spanning 0.6 to 10 degrees (67-1110 km) and occurred between 2001 and 2005. Multiple linear regression of amplitude against epicentral distance in log-log space was applied to all events. Preliminary results show an Lg-amplitude decay of 0.57 log (amplitude) per log degree of distance, a value lower than the .90 found by Nuttli (1973) and Herrmann and Kijko (1983) for distances less than 4 degrees in eastern North America in general. Ongoing study will apply rigorous variance estimates to these regressions and will examine the dependence of the decay values on regional geologic parameters such as thickness of Paleozoic cover and the location of the Precambrian Grenville front.