Corection for focal mechanism in body-wave magnitude determination

A method has been developed for considering the effect of the radiation pattern on the determination of the body-wave magnitude. The focal mechanism solutions of one intermediate and four deep-focus earthquakes analyzed in this study were determined from 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. The results of magnitude computations from the data at different stations for each of these earthquakes are presented. The application of the method to the data of the five earthquakes studied by using the values of S. J. Duda (1969)2 reveals definite improvements in the determination of the magnitudes from the vertical component of P waves. The method does not, in general, improve the results for magnitudes determined from the horizontal components of S waves. The need for a more accurate chart for values as a function of depth and epicentral distance is emphasized. The results determined for the other earthquakes studied are given in a tabular appendix, which is available on microfiche along with the entire article. Order from the American Geophysical Union, Suite 435, 2100 Pennsylvania Ave., N.W., Washington, D.C. 20037. Document J70-002; $1.00. Payment must accompany order.