GNSS观测的九寨沟7.0级地震同震位移初步结果

2017年8月8日四川省九寨沟县发生了7.0级地震，中国大陆构造环境网络与北斗地基增强系统的GNSS连续观测共同监测到了此次地震的同震位移（坐标：东向为正，北向为正），结果显示：3个站点记录到了明显的同震位移，距离震中43 km的九寨沟台站（SCJZ）在东西向的位移为-9.8±1.5 mm，在南北向的位移为3.3±0.7 mm；距离震中65 km的松潘站（SCSP）在东西向的位移为-1.8±0.7 mm，在南北向的位移为-7.7±0.6 mm；距离震中77 km的舟曲站（GSZQ）在东西向的位移为0.4±1.2 mm，在南北向的位移为3.6±0.8 mm.通过同震位移分布特征，可以推测此次地震为一次左旋走滑型事件，引起水平向同震位移大致不超过150 km范围，地震对东南侧的龙门山断裂带影响非常小，对北侧的塔藏断裂和西侧的岷江断裂处引起的同震位移为厘米级.同震位移的反演结果显示：断层面上滑动量主要集中在7 km深度，最大量值约为0.4 m，平均滑动角为-15°，利用滑动分布计算的相应矩震级为M_W6.4，与地震波反演结果相当.结合同震滑动分布、同震主应变分布、余震分布和震源机制解等特征，推测此次地震破裂极值区累积的能量得到较充分释放，进一步分析得出此次地震在塔藏断裂、岷江断裂和虎牙断裂处产生了一定的应力变化，值得持续关注.

Coseismic displacements of the 2017 Jiuzhaigou M7.0 earthquake observed by GNSS: Preliminary results

On 8 August 2017 an earthquake of magnitude 7.0 struck Jiuzhaigou, Sichuan Province. Coseismic displacements of this event have been captured by both the GNSS continuous stations of the Tectonic and Environmental Observation Network of Mainland China and the Ground Reinforcement System (coordinates:east is positive, north is positive). The results show that of three sites of the above observation have recorded obvious coseismic horizontal displacements. Of them, the SCJZ site 43 km to the epicenter observed a displacement of -9.8±1.5 mm in the east-west direction and 3.3±0.7 mm in the north-south direction, respectively. The SCSP site 65 km to the epicenter measured displacement of -1.8±0.7 mm in the east-west direction and -7.7±0.6 mm in the north-south direction, respectively. At GSZQ site, 77 km to the epicenter, displacements of 0.4±1.2 mm in the east-west direction and 3.6±0.8 mm in the north-south direction were detected. The distribution of these coseismic displacements suggests that the earthquake is a sinistral strike-slip event, causing the horizontal deformation within an extent less than 150 km with a very small effect on the Longmenshan fault zone in the southeast. The displacements on the Tazang fault and the Minjiang fault reach several centimeters. The results of inversion of the coseismic displacements show that the slip on the fault plane is mainly concentrated around 7 km depth, with maximum about 0.4 m and an average slip angle -15°. The corresponding moment magnitude calculated by the slip distribution is about M_W6.4, which is equivalent to that from seismic wave inversion. Based on the characteristics of coseismic slip distribution, principal strain distribution, aftershock distribution and focal mechanism solutions, it is inferred that the energy accumulated in the extreme area of the earthquake rupture is fully released, causing a significant stress change on the Tazang fault, the Minjiang fault and the Huya fault, which should receive continual attention.