2017年四川九寨沟Ms7.0地震InSAR同震形变场及发震构造探讨

2017年8月8日四川省九寨沟县发生M_s7.0级地震，构造部位处于青藏高原东缘的巴颜喀拉地块东北角，震中位置是岷江断裂、塔藏断裂、虎牙断裂和雪山梁子断裂围闭的空震区。哪条断裂发震，如何界定其与周边活动断裂的关系，与青藏高原东缘近年来发生的大地震是否有成因联系等问题对于理解该区域现今构造活动模式、预判地震发展趋势和部署地震地质灾害防控等工作具有重要意义。利用地震前后两期Sentinel-1合成孔径雷达数据对地表同震形变场进行了InSAR测量，获取了极震区约2000 km²范围内的雷达视线向变形（-13~28 cm）和运动方向，呈现为主动盘单侧走滑兼逆冲的变形模式，结合震源机制、断裂展布、构造背景和近年地震迁移的分析，揭示了控震构造是巴颜喀拉地块北缘边界断裂弧形旋转体系的尾端构造，发震断层是该断裂系中塔藏断裂的南段，并有与虎牙断裂贯通的趋势，因此，应重视本次地震与虎牙断裂之间的空震区未来的强震危险性问题；从区域上看，此次九寨沟地震可能与汶川地震具有一定的时空成因联系，因在巴颜喀拉地块南北边界断裂破裂基本贯通的条件下，2008年汶川地震诱发的东缘中部锁固破裂导致块体加速向东挤出，2013年鲁甸地震又释放了东缘南段挤压构造应力，从而进一步加剧了东北角的应力集中，促使九寨沟地震的发生。

INSAR CO-SEISMIC DEFORMATION OF 2017 Ms 7.0 JIUZHAIGOU EARTHQUAKE AND DISCUSSIONS ON SEISMOGENIC TECTONICS

An M_s7.0 earthquake occurred in Jiuzhaigou county on Aug. 8, 2017. Tectonic location is the NE part of Bayan-Har block, with epicenter in the earthquake-free zone surrounded by Minjiang fault, Tazang fault, Huya fault as well as Xueshanliangzi fault, and where is of free earthquake zone. Which is the seismogenic fault? How to define the relationship between this earthquake and the neighbor faults? Does it have the causal association with huge earthquakes in recent years? The answers to those questions are of great significance to understand the current tectonic activity pattern, predict seismic development trend and deploy earthquake geological disaster prevention and control. Using two periods of Sentinel-1 SAR data to carry out InSAR survey, co-seismic deformation (-13~28 cm) and movement direction within 2000 km² in meizoseismal area were measured, showing passive singe wall strike-slip and thrust ground deformation. Based on analysis of focal mechanism solution, fault distribution, tectonic background and recent seismic migration, conclusions are made as follows. The seismogenic structure is the end structure of an arc rotation system in northeastern boundary of Bayan-Har block, and the seismogenic fault is the southern branch of Tazang fault, with the trend to connect with Huya fault, therefore, the section between them should be paid more attention to in the future. There are certain spatio-temporal genetic relation between Jiuzhaigou earthquake and Wenchuan earthquake: in condition of ruptures existed in north and south boundary of Bayan-Har block, the 2008 Wenchuan earthquake induced new rupture in east edge to accelerate block eastward extrusion, and 2013 Ludian earthquake released tectonic stress in southern section, further exacerbating stress concentration in northeastern angle, which led to the 2017 Jiuzhaigou earthquake.