东昆仑断裂带东端的构造转换与2017年九寨沟MS7.0地震孕震机制

2017年四川九寨沟M_S7.0地震是继2008年汶川M_S8.0地震和2013年芦山M_S7.0地震之后，青藏高原东缘在不到十年的时间内发生的第三个震级M_S7.0以上的强震.这次地震发生在东昆仑断裂带东端，作为青藏高原东北缘的一条大型左旋走滑断裂带，东昆仑断裂带与东端其它构造之间的转换关系仍不清楚，因区内地质构造和地形复杂，东昆仑断裂带东端的主要构造仍缺少深入的研究.本文在总结区域地震构造活动特征、历史地震和现代地震基础上，通过东昆仑断裂带东端已有的和最近开展的活动构造定量研究结果，并结合现今GPS变形场资料和2017年九寨沟M_S7.0地震灾害特征分析，发现东昆仑断裂带最东段塔藏断裂上的左旋走滑除了一小部分继续向东传播转移到文县断裂带上外，大部分转化为其南侧的龙日坝断裂带北段、岷江断裂和虎牙断裂上的近东西向地壳缩短，这可能是岷山隆起的构造机制，而2017年九寨沟M_S7.0地震正是左旋走滑的东昆仑断裂带在东端继续向东扩展的结果.

Tectonic transformation at the eastern termination of the Eastern Kunlun fault zone and seismogenic mechanism of the 8 August 2017 Jiuzhaigou MS7.0 earthquake

On 8 August 2017, the Jiuzhaigou M_S7.0 earthquake following the Wenchuan M_S8.0 earthquake and the Lunshan M_S7.0 earthquake is the third strong shock in the past 10 years in the eastern margin of the Tibetan Plateau. The 2017 Jiuzhaigou earthquake occurs at the eastern termination of the Eastern Kunlun fault zone. The tectonics relationship between the Kunlun fault zone, one of the large-scale left-lateral strike-slip faults in northeastern Tibet, and other major active tectonics around its eastern tip, remains unclear. Due to complicated geology, tectonics and topography, the quantitative study on the late-Quaternary activity of the major tectonics in this region is lack. In this paper, we collected the published and newly finished work on the quantitative results on the major tectonics including the northern Longriba fault zone, Minjiang, Huya, and Wenxian faults, based on the summary of regional seismogenic tectonics, historical and instrumental earthquakes. We also analysize the GPS velocity field and spatial distribution of coseismic geological disasters of the 2017 Jiuzhaigou earthquake. Our results show that only a small patch of left-slip on the Tazang fault, easternmost segment of the Eastern Kunlun fault zone, was transferred on to the Wenxian fault zone, whereas most part was transformed into nearly north-south-striking Northern Longriba, Minjiang, and Huya faults south of Tazang fault, resulting into the uplift of the Min Shan Mountain. The 2007 Jiuzhaigou earthquake is the result of the ongoing eastward propagation of left-slip on the Kunlun fault zone at its eastern termination.