SURFACE-WAVE MAGNITUDE OF EARTHQUAKES AND ITS STATION CORRECTION

In this paper, we have described the derivation of the formula currently used in China for surface-wave magnitude determination at the Beijing Seismic Station. The following formula is used: Ms=log(A/T)max+(△).Taking the surface wave magnitude of the Pasadena Seismic station given by Gutenberg and Richter, as the standard magnitude, the calibrating function of the surface-wave magnitude (△) and formula for the Beijing Seismic Station has been derived by using the mean value of surface-wave magnitudes with the Pasadena standard from 6 well-known seismic stations in the world. The calibrating function (△) was determined empirically for distances A= 8-130as follows:(△)=(1.660.09)log△+(3.500.14) In the epicentral distances △=130-180, a modification is made for the absorption coefficient k, thus the formula of the calibrating function derived semi-empirically and semi-theoretically is expressed as follows: (△)=6.775+1/2[(2.147e-0.04465△+1.325)(△-90)10-2logsin△+1/3(log△-1.954)] In order to improve the accuracy of the surface-wave magnitude determinations, the standard of the Beijing station is extended to be used in 12 basic seismic stations in China. The station correction of each seismic station has been calculated by using the data of 360 earthquakes, thus improving the consistency for determining the surface-wave magnitudes.