Lg-Wave Attenuation Across Ohio
Jessica L. Brandeberry
2005, Ohio University Senior Thesis
Seismograms for 15 regional earthquakes were analyzed to determine the effective seismic amplitude attenuation with distance across Ohio. Lg-wave amplitudes were obtained from up to 16 OhioSeis stations, which record vertical motion with a sampling 10 Hz rate over a 0.05-1.5 Hz band. The events studied ranged from 2.0 to 5.4 in magnitude and occurred between 2001 and 2005. Stations with epicentral distance less than 56km were excluded to avoid near-field effects. Multiple linear regression of amplitude against epicentral distance in log-log space was applied to all events. The entire data set shows a log amplitude vs. log distance slope of -1.10 ±0.02. The data set was then divided based on epicentral distance (greater than or less than 4º) and also based on station position relative to the north-south trending basement Grenville front to allow comparison with standard amplitude/distance relations of Nuttli (1973). The results show that for log distances (in degrees) less than 0.6, the log amplitude vs. log distance slope of -0.62 ±0.04 was different from Nuttli's slope of -0.90. Seismograph stations east of the Grenville front and with a log distance less than 0.6 had a slope of -0.98 ±0.7, whereas those west of the Grenville front and with a log distance less than 0.6 had a slope of -3.6 ±0.9. Although more events need to be recorded and analyzed, these results imply that Ohio's "non-standard" wave propagation techniques need to be taken into account when calculating earthquake magnitudes from recorded wave amplitudes.
Last update August 04, 2005