2008年5月12日汶川MW 7.9地震的震源位置与发震时刻

综合运用四川省地震台网与紫坪铺水库地震台网的观测资料，精确地测定了2008年5月12日汶川MW7.9地震的震源位置与发震时刻．指出，对汶川地震这样的大地震精准定位，必须克服或尽量减少远台观测对地震精确定位的局限性、地壳介质模型的不完善性以及识别与检测初至波震相的不一致性等因素的影响．通过分析对比、反复试验，从上述台网中精心选取了方位分布均匀、具有近震源台站约束、直达P波震相确系由初始破裂辐射出的15个地震台的直达P波到时数据，反演得出精确度比区域性地震台网常规测定的精确度高一个数量级的汶川大地震的定位结果，即:发震时刻（北京时间）:2008年5月12日14:27:57.59plusmn;0.03 s；震中位置:31.018deg;Nplusmn;0.3 km，103.365deg;Eplusmn;0.3 km；震源深度:15.5 kmplusmn;0.3 km． 

The hypocenter and origin time of the MW7.9 Wenchuan earthquake of May 12, 2008

The hypocenter and origin time of the MW7.9 Wenchuan earthquake of May 12,2008,were relocated precisely using the observation data from both of the Sichuan Province Seismic Network and the Zhipinpu Reservoir Seismic Network.It is pointed out that the factors affected significantly to the precise and accurate determination of the hypocenter and origin time of the great earthquakes such as the Wenchuan earthquake are the limitation of far stations,incompleteness of the crust model used for earthquake location,and the inconsistency existed in the direct P phases detected from the near-by seismic stations and the far stations being generated from different rupture areas and at different times.To diminish the limitation caused by these factors,data from the local seismic stations were analyzed,and from these stations,15 near-by stations of epicentral distance of 5—160 km,with well azimuthal distribution,and with accurately correlated direct P phases were selected for inversion.The preferred relocated source parameters,obtained from inversion,have coordinates latitude 31.018°N±0.3 km,longitude 103.365°E±0.3 km,focal depth 15.5 km±0.3 km,origin time(Beijing Time) May 12,2008,14:27:57.59±0.03 s.