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Analysis of body-wave spectra for earthquake energy determination

DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES SAINT LOUIS UNIVERSITY, ST. LOUIS, MISSOURI 63156

Abstract

This study examines the body wave spectra of earthquake signals for the estimation of energy in the seismic waves by taking into account the radiation pattern of the source, the effect of geometrical spreading and absorption in the earth's mantle, the effect of crustal structure under the receiver and the response of the recording instruments. The focal mechanism solutions of one intermediate and four deep focus earthquakes analyzed in this study have been determined using the P wave first motion directions and the S wave polarization angles. All the mechanism solutions are well determined and conform to a double couple source model. In all 155 P wave time signals and 224 S wave time signals have been analyzed. The basic equations for estimating the energy in body waves from the spectra equalized to the source are discussed. The main uncertainties in the energy estimates are most likely due to the inadequate knowledge of the effect of absorption, which is quite significant at the high frequencies. Most of the low frequency energy is carried by the S waves. The ratio E_P/E_S varies between .008 to .106 for the frequency range .005 to .205 cps. The possibility of a small tensile component accompanying the shear faulting is indicated.

Footnotes

^* Now at the Seismographic Station, University of California, Berkeley, California 94720.

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