2020年阿拉斯加Mw7.8地震震源特征及邻区地震危险性分析

2020年7月22日,在美国阿拉斯加半岛南部发生了一次M W7.8地震.本文利用远场地震波形记录与近场GPS台站同震位移资料,反演了本次地震震源机制和震源破裂过程.结果表明:阿拉斯加地震为一震源深度为23 km,地震断层倾角约17°,破裂面上最大的同震位移达到914 cm的逆冲型地震.由此得到该地震的地震矩为6.94×10^20 N·m,地震震级为M W7.8.此外,破裂并非简单的以震源为中心对称分布,此次地震的破裂方向和余震分布,大体上均呈SW向延伸的趋势.本次地震破裂了舒马金空区东段,结合板块汇聚速率和断层闭锁程度计算结果表明,舒马金地震空区东段有发生8级地震的潜在危险.在地震复发周期上,舒马金西段与东段有不同的间隔,两者可能处于不同的地震周期阶段.

Source characteristics of the 2020 Alaska Mw7.8 earthquake and seismic risk analysis of adjacent areas

On July 22,2020,an earthquake with M W7.8 occurred in the southern part of Alaska Peninsula,USA.In this paper,the focal mechanism and rupture process of this earthquake are inversed with the far-field seismic waveform records and coseismic displacement data of near-field GPS stations.The results show that the Alaskan earthquake is a thrust type earthquake with a focal depth of 23km,a fault dip of about 17°,and a maximum coseismic displacement of 914cm on the fracture surface.The seismic moment of the earthquake is 6.94×10^20 N·m and the magnitude is M W7.8.In addition,the rupture is not simply symmetrically distributed around the source.The rupture direction and aftershock distribution of the earthquake generally show a SW extension trend.According to the calculation results of plate convergence rate and fault locking ratio,the eastern segment of Shumagin seismic gap is capable of M 8 earthquake.In terms of recurrence period,there are different intervals between the western and eastern segments of Shumagin,and they may be in different seismic periods.