Seismic wave phase-velocity variations in the State of Ohio
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Date
2010-03
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The Ohio State University
Abstract
Ohio has experienced at least 200 earthquakes of magnitude 2.0 or greater since 1776. (Hansen, 2009) The objective of this study was to determine if the wave phase velocities of local or regional events vary as the waves travel across Ohio and if a revision of the currently used Anna velocity model for epicenter location is necessary. It is suspected that the deep bedrock structures such as the Grenville Front Tectonic Zone, as well as differences in basement lithology might affect the velocity of seismic waves. To investigate this possibility, seismograms were acquired from the archives of the OhioSeis Network. The arrival times of Pn, Pg, Sn and Sg of well-recorded regional and local earthquakes were then determined. An inversion program was used to evaluate the accuracy of these arrival times. The input was adjusted when high residuals indicated such a necessity. Resulting wave-phase velocities were then assigned to specific geographic scenarios, which allowed the calculation of average velocities for a large number of earthquakes. The data suggest a possible increase of velocity in all wave phases from the west to the east as seismic waves travel through Ohio.
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Keywords
wave phase velocities, seismicity in Ohio, OhioSeis, Ohio Seismic Network, earthquakes in Ohio