THE COSEISMIC SOURCE SLIP AND COULOMB STRESS TRIGGERING OF 2015 NEPAL GORKHA MW7.9 AND KODARIMW7.3 EARTHQUAKE BASED ON InSAR MEASUREMENTS

doi:10.3969/j.issn.0253-4967.2017.01.008

Abstract

Abstract:

According to the structure of the Himalayan orogenic belt, a low-angle antilistric thrust-slip fault model is used to simulate the ramp on the rupture portion of the Main Himalayan Fault. Based on descending Alos -2 and Sentinal -1 data, we invert for the coseismic slip models of the Gorkha earthquake and its largest aftershock, Kodari earthquake. In contrast to the inversion using Alos -2 or Sentinal -1 separately, the joint inversion of both data sets has stronger constraint for the deep slip and can obtain more details in Gorkha earthquake. The rupture depth obtained by joint inversion can be as deep as 24km underground, cutting across the locking line to the transition of locked and the creeping zone. The largest slip is as large as 4.5m appearing 17km underground and the dip angle is between 3°and 10°. Gorkha and Kodari earthquakes have the similar focal mechanisms, both of which are mainly thrusting, and yet some right-lateral slip component in Gorkha earthquake. The inversion results reveal that slip models of the Nepal mainshock and its largest aftershock are complementary in space and the Kodari earthquake occurs in the gaps of slip in Gorkha earthquake. The epicenter of the Kodari earthquake is just right in the transitive zone of the positive and negative Coulomb stress change, where the Coulomb stress change can reach 0.4MPa. We thus argue that Kodari earthquake has been triggered by the Gorkha earthquake.

Key words: Nepal GorkhaM_W7.9 earthquake, coseismic slip inversion, rupture model, stress triggering

摘要：

根据喜马拉雅断裂系的构造形态，采用缓倾角反铲型断层模型模拟MHT上地震破裂部分的坡坪式发震构造。利用Alos-2及Sentinel-1获取的InSAR数据，反演获得了2015年尼泊尔Gorkha地震及其最大余震Kodari地震的同震滑动分布模型。与单独利用Alos-2或Sentinel-1 InSAR数据的反演结果相比，利用Alos-2和Sentinel-1 InSAR数据联合反演能够提供Gorkha地震破裂的更多细节信息，尤其对深部信息的约束更加明显。联合反演得到的破裂深度最大可达24km，穿过了该区域的闭锁线，到达了闭锁和蠕滑的转换区域。反演的断层模型倾角在3°~10°之间，最大滑动量出现在地下17km处，约4.5m。Gorkha地震和Kodari地震发震性质相似，都是发生在MHT断层上的低角度逆冲型地震，其中Gorkha地震略带右旋分量。反演结果还显示，Gorkha地震与Kodari地震的破裂滑动在空间上存在互补性，Kodari地震就发生在Gorkha地震的破裂空区内。通过计算Gorkha地震对Kodari地震发震断层的库仑破裂应力加载，发现Kodari地震震中恰位于库伦破裂应力正负交界区域，库仑破裂应力加载达0.4MPa，表明Kodari地震可能受到了Gorkha地震的触发。

关键词: 尼泊尔Gorkha M_W7.9地震, 同震滑动分布反演, 破裂特征, 应力触发

CLC Number:

P315.72⁺7

ZHANG Ying-feng, ZHANG Guo-hong, SHAN Xin-jian, WEN Shao-yan. THE COSEISMIC SOURCE SLIP AND COULOMB STRESS TRIGGERING OF 2015 NEPAL GORKHA M_W7.9 AND KODARIM_W7.3 EARTHQUAKE BASED ON InSAR MEASUREMENTS[J]. SEISMOLOGY AND GEOLOGY, 2017, 39(1): 104-116.

张迎峰, 张国宏, 单新建, 温少妍. 2015年尼泊尔GorkhaM_W7.9地震与KodariM_W7.3地震InSAR数据反演及其应力触发分析[J]. 地震地质, 2017, 39(1): 104-116.

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