Abstract: A strong earthquake with magnitude M_S6.2 hit Hutubi, Xinjiang at 13:15:03 on December 8th, 2016(Beijing Time). In order to better understand its mechanism, we performed centroid moment tensor inversion using the broadband waveform data recorded at stations from the Xinjiang regional seismic network by employing gCAP method. The best double couple solution of the M_S6.2 mainshock on December 8th, 2016 estimated from local and near-regional waveforms is strike:271°, dip:64ånd rake:90° for nodal plane I, and strike:91°, dip:26ånd rake:90°for nodal plane Ⅱ; the centroid depth is about 21km and the moment magnitude(M_W)is 5.9. ISO, CLVD and DC, the full moment tensor, of the earthquake accounted for 0.049%, 0.156% and 99.795%, respectively. The share of non-double couple component is merely 0.205%. This indicates that the earthquake is of double-couple fault mode, a typical tectonic earthquake featuring a thrust-type earthquake of squeezing property.The double difference(HypoDD)technique provided good opportunities for a comparative study of spatio-temporal properties and evolution of the aftershock sequences, and the earthquake relocation was done using HypoDD method. 486 aftershocks are relocated accurately and 327 events are obtained, whose residual of the RMS is 0.19, and the standard deviations along the direction of longitude, latitude and depth are 0.57km, 0.6km and 1.07km respectively. The result reveals that the aftershocks sequence is mainly distributed along the southern marginal fault of the Junggar Basin, extending about 35km to the NWW direction as a whole; the focal depths are above 20km for most of earthquakes, while the main shock and the biggest aftershock are deeper than others. The depth profile shows a relatively steep dip angle of the seismogenic fault plane, and the aftershocks dipping northward. Based on the spatial and temporal distribution features of the aftershocks, it is considered that the seismogenic fault plane may be the nodal plane I and the dip angle is about 271°. The structure of the Hutubi earthquake area is extremely complicated. The existing geological structure research results show that the combination zone between the northern Tianshan and the Junggar Basin presents typical intracontinental active tectonic features. There are numerous thrust fold structures, which are characterized by anticlines and reverse faults parallel to the mountains formed during the multi-stage Cenozoic period. The structural deformation shows the deformation characteristics of longitudinal zoning, lateral segmentation and vertical stratification. The ground geological survey and the tectonic interpretation of the seismic data show that the recoil faults are developed near the source area of the Hutubi earthquake, and the recoil faults related to the anticline are all blind thrust faults. The deep reflection seismic profile shows that there are several listric reverse faults dipping southward near the study area, corresponding to the active hidden reverse faults; At the leading edge of the nappe, there are complex fault and fold structures, which, in this area, are the compressional triangular zone, tilted structure and northward bedding backthrust formation. Integrating with geological survey and seismic deep soundings, the seismogenic fault of the M_S6.2 earthquake is classified as a typical blind reverse fault with the opposite direction close to the southern marginal fault of the Junggar Basin, which is caused by the fact that the main fault is reversed by a strong push to the front during the process of thrust slip. Moreover, the Manas earthquake in 1906 also occurred near the southern marginal fault in Junggar, and the seismogenic mechanism was a blind fault. This suggests that there are some hidden thrust fault systems in the piedmont area of the northern Tianshan Mountains. These faults are controlled by active faults in the deep and contain multiple sets of active faults.

Key words: the Hutubi earthquake in Xinjiang, earthquake location, focal mechanism, blind backthrust fault

摘要： 北京时间2016年12月8日13时15分03秒，新疆呼图壁发生了M_S6.2地震。为了更好地了解此次地震的发震机理，文中利用新疆区域台网波形记录，采用gCAP （generalized Cut and Paste）方法，反演得到2016年12月8日新疆呼图壁M_S6.2地震主震的最佳双力偶节面解，其中节面Ⅰ走向271°、倾角64°、滑动角90°；节面Ⅱ走向91°、倾角26°、滑动角90°；最佳矩心深度为21km，矩震级M_W5.9。之后采用HypoDD方法，对468个地震事件进行相对定位，得到327个重新定位事件，结果显示地震序列整体沿NWW向分布，展布长度约35km；震源深度主要集中在20km以内，主震和较大余震震源深度较深；深度剖面显示发震断层面倾向为NNW向，与北天山山前逆冲推覆构造的总体逆冲方向相反，结合周围野外地质构造和深地震剖面结果分析，其发震断层极有可能是位于准噶尔盆地南缘断裂附近的一条隐伏反冲断层。

关键词: 新疆呼图壁地震, 地震定位, 震源机制, 隐伏反冲断层