Abstract: On November 18, 2017, a M_S6.9 earthquake struck Mainling County, Tibet, with a depth of 10km. The earthquake occurred at the eastern Himalaya syntaxis. The Namche Barwan moved northward relative to the Himalayan terrane and was subducted deeply beneath the Lhasa terrane, forming the eastern syntaxis after the collision of the Indian plate and Asian plates. Firstly, this paper uses the far and near field broadband seismic waveform for joint inversion (CAPJoint method)of the earthquake focal mechanism. Two groups of nodal planes are obtained after 1000 times Bootstrap test. The strike, dip and rake of the best solution are calculated to be 302°, 76° and 84° (the nodal plane Ⅰ)and 138°, 27° and 104° (the nodal plane Ⅱ), respectively. This event was captured by interferometric synthetic aperture radar (InSAR)measurements from the Sentinel-1A radar satellite, which provide the opportunity to determine the fault plane, as well as the co-seismic slip distribution, and assess the seismic hazards. The overall trend of the deformation field revealed by InSAR is consistent with the GPS displacement field released by the Gan Wei-Jun's team. Geodesy (InSAR and GPS)observation of the earthquake deformation field shows the northeastern side of the epicenter uplifting and the southwestern side sinking. According to geodetic measurements and the thrust characteristics of fault deformation field, we speculate that the nodal plane Ⅰ is the true rupture plane. Secondly, based on the focal mechanism, we use InSAR data as the constraint to invert for the fine slip distribution on the fault plane. Our best model suggests that the seismogenic fault is a NW-SE striking thrust fault with a high angle. Combined with the slip distribution and aftershocks, we suggest that the earthquake is a high-angle thrust event, which is caused by the NE-dipping thrust beneath the Namche Barwa syntaxis subducted deeply beneath the Lhasa terrane.

Key words: Mainling earthquake, regional and teleseismic joint inversion, focal mechanism, InSAR deformation filed, high-angle thrust event

摘要： 北京时间2017年11月18日6时34分在西藏林芝市米林县发生6.9级地震，震源深度10km。本次地震发生在由印度板块向欧亚板块碰撞形成的喜马拉雅造山带的东端构造急剧转向的东构造结南迦巴瓦地区。文中首先采用远、近场的宽频带地震波波形联合反演（CAPJoint）了本次地震的震源机制，经过Bootstrap法测试后得到2组节面，节面Ⅰ的走向、倾角和滑动角依次为302°、76°和84°，节面Ⅱ的走向、倾角和滑动角依次为138°、27°和104°。接着利用Sentinel-1A卫星数据获取了InSAR同震形变场，所得到的形变场总体趋势同甘卫军研究小组发布的GPS同震位移场相吻合。大地测量（InSAR和GPS）的形变场显示北东盘隆升而南西盘下沉，结合大地测量的观测结果及逆冲断层形变场应有的特征，推测节面Ⅰ应为发震断层面，断层倾向NE。在此基础上使用InSAR观测数据作为约束进行了滑动分布反演，并结合短期余震的分布情况，认为发震断层为一高角度逆冲断层，本次地震可能是由南迦巴瓦变质体复式背形构造北侧向N倾斜楔入拉萨地体而引发。

关键词: 米林地震, 近远震联合反演, 震源机制解, InSAR形变场, 高角度逆冲地震