Determination of the surface-wave magnitude of the Wenchuan earthquake and its seismic Doppler effect

The fast report and revision of the parameters of the Wenchuan earthquake on 12 May 2008 by some major international seismological institutions are introduced, and the surface-wave magnitude measured by National Earthquake Information Center of United States Geological Survey is analyzed in this paper. The comparison of the measured surface-wave magnitudes and periods of 198 global seismic stations reveals that, those stations with larger magnitudes are mainly in NE direction of the epicenter while those with smaller magnitudes are in SW and SE direction, and stations with smaller periods are mainly in NE direction. The seismic intensity map of the Wenchuan earthquake shows that the intensity attenuated slowly in the NE direction of the central fracture zone while the intensity attenuated fast in the SW direction. The reason is that Wenchuan earthquake is a unilateral rupture mainly in NE direction, due to the seismic Doppler effect, the stronger shaking leads to the larger surface-wave magnitudes and slower intensity attenuation in the NE direction of the epicenter, vice versa the weaker shaking leads to the smaller surface-wave magnitudes and faster intensity attenuation in the SW direction.