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ON THE SURFACE WAVE MAGNITUDE MEASURED BY THE SEISMIC NETWORK IN CHINA

CHEN PEI-SHAN(Institute of Geophysics, State Seismological Bureau, Beijing)YE WEN-HUA(Institute of Geology, State Seismological Bureau, Beijing)  
A comparison of the surface wave magnitudes determined recently by four largest networks: ----the global network" used by International Seismological Centre (ISC), the USA network by NEIS, the USSR network(MOS), and the Chinese network (PEK)in the world:has been made. It is Sound that the three magnitudes which are determined by ISC, NEIS, MOS respectively are consistent, and there is no systematic difference among them. But the magnitude (M s,PEK) measured recently in China is not consistent with those by the previous three networks, and 0.13 larger on average than MS,ISC determined by ISC. The error of the magnitude is,0.27 compared with the MS.ISC,This situation should be improved.Authors used a new calibration function Osoc(A) of the surface wave magnitude. This calibration function is based on the theory of the surface wave propagation, considering this factors of geometrical spreading, inelastic absorption,, dispersion attenuation, the effect of seis- mograph and variation of predominant period of surface wave with epicentral distance, and taking Q value 300 on average over the globe. It is consistent with the calibration function OIASPEI(△) recommended by IASPEI in the range of epicentral distance △=20°-160°, and extended the valid range of OIASPEI(△)to the epicentral distance from 1.0° to 179° and for the surface wace period from 7.5 second to 30 second. Therefore, it is much more suitable to the seismic network which consists of broad-band seismographs SK with moderate period in China. If the calibration function O300(△) is adopted and is corrected to azimuth, there will be no difference between the surface wave magnitude measured by seismic network in China and that from the ISC, and the error of the magnitude will drop to 0.19, the same as the error by USSR network.
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