Magnitude Determination for Larger Kern County Shocks, 1952; Effects of Station Azimuth and Calculation Methods

Abstract

Methods for magnitude determination are summarized. Values for the magnitude of the main shock are listed on the basis of wave amplitudes measured on seismograms of individual stations. About 200 data from body wave amplitudes result in a magnitude of 7.6 with only slight variation in azimuth. However, amplitudes of surface waves at a given distance show a clear variation with the azimuth in which they start with a maximum towards northeast (in the direction of the fault) about 10 times the minimum which is found in waves starting towards southwest. This is considered to be a consequence of the fact that in the main shock the breaking proceeded northeastward from the neighborhood of the southwest end of the active fault segment. In the largest aftershocks there was no appreciable difference in the amplitudes of surface waves in those azimuths for which data are available. The magnitude of the main shock determined from surface waves is 7.6 to 7.7. Magnitudes of the largest aftershocks are listed. They are calculated from maximum amplitudes at near-by stations, from amplitudes of body waves at distant stations, and from surface waves. The differences between the various results for a given shock are relatively small.

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