Determination of parameters for the 20 April 2013 Lushan M_W6.7(M_S7.0) earthquake in Sichuan Province

After the Lushan M_W6.7(M_S7.0) earthquake on 20 April, 2013 in Sichuan Province, this paper revised the earthquake parameters rapidly issued by China Earthquake Networks Center (CENC), based on the data from 97 stations of China National Seismic Network. The results are: the origin time of the earthquake is 08:02:47.5 Beijing time (00:02:47.5 UTC), the epicenter is located at (30.30°N, 102.99°E) and the focal depth is 17 km; the surface wave magnitude of the earthquake is M_S7.0, the short period body wave magnitude is m_b6.0 and the moderate-long period body wave magnitude is m_B7.0. The focal mechanisms are calculated by waveform inversion and the two nodal planes of the best double couple solution are: for the nodal plane Ⅰ strike 17°/dip 48°/slip 80°, and strike 212°/dip 43°/slip 101° for the nodal plane Ⅱ; the moment magnitude is M_W6.7. In addition, in view of the fact that the magnitude issued by CENC is M_S7.0, while that by USGS/NEIC is M_W6.6, so it is suggested that China should issue M_W as the preferred magnitude so as to make the magnitude report in accordance with international convention.