2020年新疆于田MS6.4地震断层面快速测定及发震构造研究

本文基于新疆、 西藏区域数字地震台网波形数据, 利用gCAP反演方法和空间格点搜索算法获得2020年6月26日于田M_S6.4地震矩心的空间位置为35.649°N, 82.339°E, 深度为5 km。 最佳震源机制解节面Ⅰ走向166°, 倾角59°, 滑动角-144°; 节面Ⅱ走向26°, 倾角38°, 滑动角-55°, 矩震级为M_W6.21。 根据不同震源机制解结果, 获得中心震源机制解和标准差, 表明震源机制解较为稳定和可靠。 使用H-C方法进行地震发震断层的快速判断, 显示节面Ⅱ为发震断层面。 综合震源区地质构造特征、 余震序列的空间分布和区域构造应力场特征, 最终推断此次地震断层面为节面Ⅱ, 阿尔金断裂西段是发震断层, 震源机制解显示以正滑为主, 是一次张性破裂地震事件, 属于阿尔金断裂西段强烈活动的响应。

Quick Fault-plane Identification and Seismogenic Structure of the 2020 Yutian Ms6.4 Earthquake,Xinjiang

The focal mechanism solution and centroid position of the 26 June 2020 Yutian M_S6.4 Earthquake in Xinjiang Autonomous Region was studied by the gCAP method using the observed waveform from the Xinjiang and Tibet Regional Seismic Networks. The result show that centroid position is 35.649°N, 82.339°E and depth is 5 km using grid search method in the 3D vicinity of the hypocenter. The moment magnitude is M_W4.5 and the strike/dip/slip of the first nodal plane are 166°/59°/-144° and those of the second nodal plane are 26°/38°/-55°. The result’s robustness was investigated by determination of center of several focal mechanism of the same earthquake and standard deviation, the resolved focal mechanism is stable. Preliminary result show the second nodal plane is inferred to the Fault-Plane by hypocenter-centroid methods for quick identification of an earthquake fault plane, without having to wait for the occurrence of aftershocks. According to the characteristic of geologic structure in seismic source area, space distribution of aftershock sequence and characteristics of regional tectonic stress field, and combining focal mechanism of main shock, we conclude that the Yutian earthquake has normal mechanism and the second nodal plane is inferred to the seismogenic fault that agrees with the geometry of Altyn Tagh fault. The mainshock source mechanism is tensile rupture, we deduced that the mainshock is a powerful seismic activity of the western segment of the Altyn Tagh fault which is the seismogenic fault.