GPS测定的尼泊尔M_w7.9和M_w7.3级地震同震形变场

Co-seismic displacements associated with the 2015 Nepal M_w7.9 earthquake and M_w7.3 aftershock constrained by Global Positioning System Measurements

2015年尼泊尔M w7.9和M w7.3级地震致灾范围包括尼泊尔、印度北部、巴基斯坦、孟加拉和中国藏南地区,地震应变应力调整将对震区和邻区的地震活动产生不同程度的影响.尼泊尔境内的GPS连续观测数据、＂中国大陆构造环境监测网络＂GPS基准站和地震应急流动站观测数据计算结果揭示了尼泊尔地震的静态和动态同震形变场.对M w7.9级地震,尼泊尔境内近场静态同震GPS水平位移最大为1.89 m,距震中100~400 km的中国藏南地区观测到几毫米到几十厘米的静态水平位移,毗邻尼泊尔的聂拉木县最大形变54.0 cm.M w7.3级地震静态同震形变最大为2 cm,局限在震中附近200 km范围内.距震中约2000 km内的GPS基准站均记录到M w7.9大震明显的动态形变信号,高频GPS动态形变幅度与地震破裂方向有关,位于破裂方向上的测站动态形变幅度明显大于其他方向的测站.用弹性半空间位错模型正演模拟了震区和青藏高原南部格网点上的同震形变,并分析了地震应变影响,认为尼泊尔地震对中国藏南地区产生一定程度的拉张型应力变化,需要持续关注.

A magnitude of M w7.9 earthquake occurred in Nepal on 25 April 2015 along the Himalayan seismic zone. Twelve days later, a magnitude of M w7.3 aftershock ruptured the southeast side of initial rupture region of the M w7.9 earthquake. In this study, we report in detail the co-seismic displacements, which were caused by the two events, based on continuous observations in Nepal obtained from the permanent Global Positioning System（GPS） stations of the Crustal Movement Observation Network of China（CMONOC） and from campaign GPS measurements in southern Tibet before and after the M w7.9 earthquake. The largest co-seismic horizontal offset caused by the M w7.9 earthquake was 1.89, and it was reported from the KKN4 station in Nepal. In southern Tibet, the co-seismic horizontal displacements varied from several millimeters to approximately half a meter within a 100–400 km range of the epicenter. The horizontal offset in the Everest Mountains was about 3 cm. Referring to the M w7.3 earthquake, co-seismic offsets of up to 2 cm could be detected as far as approximately 200 km away from the epicenter. Near-field GPS stations also recorded significant vertical deformations caused by the great thrust earthquake. The GPS displacements in the In SAR Line of Sight（LOS） direction agreed well with the In SAR LOS values. In addition, high-rate GPS deformation waveforms were recorded by the high-rate GPS stations in China's Mainland within a distance of approximately 2000 km from the epicenter, indicating that the amplitude of the seismic waves in the direction of the fault rupture increased. The GPS stations located along the direction of seismic rupture recorded much larger deformation waveform amplitudes than those located in the opposite direction. Finally, forward calculations were performed using a simple elastic half-space dislocation model, in order to investigate the co-seismic displacements and the principle strain changes around the epicenter, especially in the southern Tibet. The principle strain results indicated that the Nepal M w7.9 earthquake resulted in the tensile stress changes in southern Tibet and probably triggered the Dingri M s5.9 earthquake.