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Title:: Seismogenic Fault of the 2016 Hutubi M6.2 Earthquake Constraint from the Borehole Strain Observations

Author(s):: BU Zhuyuan; LI Yujiang; TANG Lei; JING Yan; CHEN Lianwang; (National Institute of Natural Hazards,Ministry of Emergency Management of China,Beijing 100085,China)

Keywords:: Hutubi M6.2 earthquake; borehole strain observation; coseismic strain step; coseismic stress field; elastic dislocation theory

摘要:: 利用北天山地区的钻孔应变观测资料,分析2016年呼图壁M6.2地震同震应变阶跃的张、压性特征。结合余震精定位方法等给出的震源参数,基于弹性位错理论,模拟不同震源参数下的同震应变阶跃的张、压性特征。通过对钻孔应变张、压性的模拟值与实测值进行对比分析,研究呼图壁M6.2地震的发震断层。结果表明:① 震中附近4个四分量钻孔应变台站数据自检性能较好,且多记录到明显的同震应变阶跃,其中,呼图壁、石场、巴伦台应变阶跃较为明显,张、压性变化最大值分别达2.5×10^-8和-3.4×10^-8; ② 在地震震源参数为293°/64°/90°(走向/倾角/滑动角)、发震断层面倾向北时,钻孔应变张、压性的模拟值与实测值最为吻合,呼图壁M6.2地震的发震断层极有可能为一条倾向北的高角度逆冲型盲断层。本文结果为认识呼图壁M6.2地震的发震构造提供重要力学依据。

Abstract:: In this paper,using the borehole strain observation data in the northern Tien Shan area,we analyzed the tensile-compressive characteristics of the coseismic strain step associated with the Hutubi M6.2 earthquake.Based on different source parameters by aftershock relocation etc.,we simulated the tensile-compressive characteristics of the coseismic strain step by the elastic dislocation theory.Through comparing the tensile-compressive characteristics between the modeled and the observed results,we analyzed the seismogenic fault of the Hutubi M6.2 earthquake.The results show that:① The data of the four four-component borehole strain observation stations near the epicenter have the good self-checking performance,which also record the coseismic strain steps successfully.Among them,the strain steps at Hutubi,Shichang and Baluntai stations are more obvious,and the maximum values of the tension and compression of the coseismic strain steps are 2.5×10^-8 and-3.4×10^-8,respectively.② When the seismic source parameters are 293 ° /64 ° /90 °(strike /dip /rake)and the fault plane inclines to the north,the simulated values of strain tension and compression of borehole are fit well with the measured values,therefore we induced that the Hutubi M6.2 earthquake most likely occurred on a north-trending high-angle blind thrust fault.The results provide an important mechanical basis for understanding the seismotectonics of the 2016 Hutubi M6.2 earthquake.