• 研究论文 •

### 2019年夏河M5.7地震的余震序列重定位及发震构造

1. 1)甘肃兰州地球物理国家野外科学观测研究站, 兰州 730000;
2)中国地震局兰州岩土地震研究所, 兰州 730000;
3)中山大学地球科学与工程学院, 广州 510275
• 收稿日期:2020-01-20 修回日期:2020-04-20 出版日期:2021-02-20 发布日期:2021-05-06
• 通讯作者: *沈旭章, 男, 1976年生, 教授, 从事地球内部物理、 地震学研究, E-mail: shenxzh5@mail.sysu.edu.cn
• 作者简介:刘旭宙, 男, 1976年生, 2018年于中国地震局兰州地震研究所获固体地球物理专业硕士学位, 副研究员, 现主要从事地震学研究, 电话: 13893606625, E-mail:liuxz@gsdzj.gov.cn, 33534138@qq.com。
• 基金资助:
国家重点研发计划项目(2017YFC1500100, 2018YFC1503206); 中国地震局地震科技星火计划项目(XH18050SX); 国家自然科学基金(41674046, 41704057, 41730212)共同资助

### RELOCATION OF THE 28 OCTOBER 2019 XIAHE M5.7 EARTHQUAKE SEQUENCE AND ANALYSIS OF SEISMOGENIC FAULT

LIU Xu-zhou1),2), SHEN Xu-zhang3), HE Xiao-hui3), PU Ju1)

1. 1)Gansu Lanzhou Geophysics National Observatory and Research Station, Lanzhou 730000, China;
2)Lanzhou Institute of Geotechnique and Earthquake, China Earthquake Administration, Lanzhou 730000, China;
3)School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
• Received:2020-01-20 Revised:2020-04-20 Online:2021-02-20 Published:2021-05-06

Abstract: The Gansu Xiahe M5.7 earthquake on 28 October 2019 is located between the Lintan-Tanchang Fault and the northern Xiqinling Fault. The earthquake sequence offered significant information for interpreting the focal mechanism solution and analyzing the seismotectonics, which is helpful for the estimation of the level of future seismic risk in this region.
There are 180 aftershocks recorded by Gansu seismic network within 650 hours after the Xiahe M5.7 main shock up to November 24, 2019. The waveforms recorded by 20 seismic stations that have a distance less than 200km to the Xiahe M5.7 main shock are collected. HZT station, the nearest station to the main shock has an epicenter distance of 19km. Locations of 94 earthquakes including the main shock are obtained after locating the earthquake sequence using HYPO2000 method, each earthquake is with more than 3 recognizable Pg phases during location. The result of location shows that the aftershock epicenters are concentrated and mainly distributed in an area of 20km×20km near the epicenter of the main shock, the hypocentral locations are distributed in the depth of 1~16km.
After locating the Xiahe M5.7 main shock and the aftershock sequence, we calculated the focal mechanism of the main shock using gCAP and P waveform polarity method, and relocated the main shock and aftershocks by the method of double difference algorithm.
The results show that the parameters of the focal mechanism solution are as follows: For the nodal plane Ⅰ, strike is 185°, dip is 56°, and rake is 127°; for the nodal plane Ⅱ, strike is 312°, dip is 48°, and rake is 48°.The relocation results show the occurrence features of the seismogenic fault that dips northeast with dip angles about 47°~54°, which is near to nodal plane Ⅱ of the focal mechanism solution.
The epicenter of Xiahe M5.7 earthquake is closer to the western Lintan-Tanchang Fault, which has a complex geometry structure composed of several parallel and oblique secondary faults. Before Xiahe M5.7 earthquake, the activity of the western segment of the fault was weak. The Lintan-Tanchang main fault and its secondary faults are part of the transition zone of structural transformation between the Eastern Kunlun Fault and the north margin of West Qinling Fault, which caused several moderate earthquakes occurring near the Lintan-Tanchang Fault since 2003. The Minxian MS6.6 earthquake 2013, which is the largest earthquake of these earthquakes, has a seismogenic fault which is a secondary fault of Lintan-Tanchang Fault, this fault merges into the Lintan-Tanchang main fault in the deep part.
The result of the relocation shows that the hypocentral location of Xiahe M5.7 is not on Lintan-Tanchang main fault but on a branch fault, since the epicenter of the earthquake has a certain distance from the western segment of Lintan-Tanchang main fault. Previous studies are lacking about seismogenic fault of Xiahe M5.7 earthquake. In this paper, based on the focal mechanism of Xiahe M5.7 earthquake, which is same to the mechanisms of the moderate strong earthquakes occurring near the Lintan-Tanchang Fault in the past twenty years and the feature of Lintan-Tanchang main fault with its secondary faults, we speculated that the seismogenic fault of Xiahe M5.7 earthquake is one of the secondary faults of Lintan-Tanchang Fault, and it has the same structure as other secondary faults that the fault merges into the Lintan-Tanchang main fault in the deep part. The seismogenic fault of Xiahe M5.7 earthquake has a strike angle of about 312° and a dip angle of about 48°, the strike angle is consistent with the intensity distribution from the post-earthquake investigations.