2015年4月25日尼泊尔M_S8.1大地震的同震效应

应用有限单元方法,计算了2015年尼泊尔MS8.1大地震发生产生的同震变形和应力变化.计算中考虑地球为球体以确保远场应力场变化得到可靠结果,采用PREM模型的地球分层模型,考虑了中国地震局(CEA)和美国地质调查局(USGS)各自提供的断层滑动模型.结果表明:尼泊尔MS8.1地震是一个比较典型的低角度逆冲地震,水平位移和应力降较大;地震造成南北方向上的水平位移最突出,且集中在首都加德满都附近区域.USGS断层滑动模型地表最大位移量达到3.5m,CEA滑动模型最大为1.2m;东西向和垂直方向上的同震位移相对较小;同震位移量级在0.1m的影响区域可达300km;地震造成尼泊尔地区最大库仑应力变化可达到MPa量级,地震危险性依然较大.此次MS8.1地震对我国西藏地区有一定影响,特别是雅鲁藏布江地区和拉萨块体南北走向的正断层,库仑应力变化为正,量级可达数千帕乃至十余千帕,应该注意该区被诱发中强震的可能性.

Calculation of the co-seismic effect of MS8.1 earthquake,Apirl 25, 2015, Nepal

The co-seismic displacement and stress fields of M_S8.1 earthquake in Nepal were calculated using finite element method in this paper. Curvature of the Earth was included in our model to get accurate results in far field. We adopted the PREM earth model and two different slip models in the calculation. Nepal M_S8.1 earthquake is a typical low-angle thrust earthquake, co-deformation mainly concentrated in the horizontal plane. The co-seismic displacement is mainly in north-south direction and concentrated near Kathmandu. East-West and vertical components are relatively small. The USGS slip model gave a maximum displacement around 3.5 m, while the CEA slip model is up to 1.2 m. The range of influence is about 300 km within which co-seismic displacement is over 0.1 m. Coulomb failure stress change caused by the earthquake is positive in the vicinity of Nepal and its maximum is about several MPa. The M_S8.1 earthquake could affect China's Tibet region, especially in areas of the Brahmaputra and the Lhasa block, where Coulomb failure stress changes are positive and the magnitude is up to 10 kPa for N-S trending normal faults, which implies possibilities of triggering strong earthquakes.