东昆仑断裂滑动速率变化及其对2017年九寨沟地震的应力加载

为了解东昆仑断裂活动对2017年8月8日九寨沟M_S7.0地震的影响，本文选取1999-2007年、2013-2017年GPS速度场作为约束，基于块体-位错模型反演计算东昆仑断裂两个时间段的块体运动速率、断裂滑动速率和滑动亏损率，并进一步研究青藏高原东缘最大剪应变率场和九寨沟震区的震间库仑应力累积速率.结果显示，东昆仑断裂中西段左旋走滑速率较高，东段走滑速率较低，自西向东逐步递减，存在明显的梯度.在两个时间段，阿坝块体刚性运动的方向顺时针偏转0.2°，运动速率由12.22 mm·a^-1增大到15.96 mm·a^-1；东昆仑断裂左旋走滑速率升高，其中西段较为明显（升高约1.2±0.3 mm·a^-1）；东昆仑断裂东段闭锁深度和闭锁程度增加；2013-2017年，东昆仑断裂滑动引起的九寨沟震区库仑应力累积速率是1999-2007年的3倍，最大剪应变率也明显升高.因此本文认为：2008年汶川地震和2013年芦山地震后，龙门山断裂部分解锁，阿坝地块活动性增强，东昆仑断裂滑动速率增大，导致九寨沟震区库仑应力加载速率增加，加速了九寨沟地震的孕育过程.

Slip rate change of East Kunlun fault and its stress effect on 2017 Jiuzhaigou earthquake

In order to study the influence of the East Kunlun Fault activity on the Jiuzhaigou M_S7.0 earthquake which occurred on August 8 2017, we calculate the block motions, slip rates and slip deficits of the East Kunlun Fault during two periods of 1999-2007 and 2013-2017 based on Block-Dislocation Model and constrained by the GPS velocity fields data. And then, we study the maximum shear strain rate field on the eastern edge of the Qinghai-Tibet Plateau and interseismic Coulomb stress accumulation rate in the source area of the Jiuzhaigou earthquake. We find that the left-lateral strike-slip rate of the mid-west region of East Kunlun Fault is higher than that of east region. The overall trend of slip rate of East Kunlun Fault is progressively decreasing from west towards east with a clear gradient. In these two periods, the azimuth angles of the rigid motion of the Aba block are 164.1° and 164.3° respectively (the clockwise deflection is 0.2°) and the movement rate increases from 12.22 mm·a^-1 to 15.96 mm·a^-1. The strike-slip rate of the East Kunlun Fault increases, especially the rate of the western section increases by about 1.2±0.3 mm·a^-1 and the coupling fractions in the eastern section of the East Kunlun Fault increase and deepen after 2013, which probably are affected by 2008 Wenchuan earthquake and 2013 Lushan earthquake. The accumulative rate of interseismic Coulomb stress in the Jiuzhaigou earthquake region during 2013-2017 is three times as big as that during 1999-2007 and the maximum shear strain rate is also significantly higher during 2013-2017. This study shows that as the Longmenshan Fault gradually unlocks, the Aba block is becoming more and more active and the slip rate of the East Kunlun Fault increases, which lead to the increasing of the interseismic Coulomb stress accumulation rate in the Jiuzhaigou earthquake area and accelerating the generation of the Jiuzhaigou earthquake.