2017年9月2日宁夏固原4.6级地震震例分析

2017年9月2日宁夏固原市原州区发生4.6级地震。通过对此次地震的回顾和总结，得到以下结论：①固原4.6级地震为孤立型地震；余震主要分布在主震震中西南侧，结合震源机制节面解，初步判定NW向节面应为此次地震的发震断层面，震源错动方式为左旋走滑兼具逆冲；震源机制解最佳拟合深度为9 km；震源机制解参数为节面Ⅰ：走向34°、倾角62°、滑动角174°，节面Ⅱ：走向127°、倾角85°、滑动角28°；②固原4.6级地震前存在前震活动、小震调制异常以及固原地震窗异常；③海原小山钻孔应变异常变化与固原4.6级地震有关，且与该测项预测指标已有的研究结果较吻合，但此次地震震级比预计震级偏大；④固原地震台地电阻率和地磁谐波振幅比异常期间发生了3次中强地震，其中，2017年5月17—20日，固原地震台地电阻率EW向出现快速下降，之后呈低值变化；固原地震台地磁谐波振幅比NS向从2014年开始经历下降—转折—回升过程，具有良好的映震效能。

Analysis of Guyuan M 4.6 earthquake on September 2, 2017 in Ningxia

On September 2, 2017, an M 4.6 earthquake occurred in Yuanzhou District, Guyuan City, Ningxia Hui Autonomous Region. Based on the review and summary of the earthquake, the following conclusions can be drawn:① Guyuan M 4.6 earthquake is an isolated earthquake; aftershocks are mainly distributed in the southwest of the epicenter. Combined with the focal mechanism nodal plane solution, it is preliminarily determined that the NW-trending nodal plane should be the fault plane of this earthquake, and the source dislocation mode is both left-lateral strike-slip and reverse. Rush. The optimum fitting depth of focal mechanism solution is 9 km. The focal mechanism solution parameters are nodal I:strike 34°, dip 62° and slip 174°; nodal II:strike 127°, dip 85° and slip 28°. ② Before the Guyuan M 4.6 earthquake, there were foreshock activities, small earthquake modulation anomaly and Guyuan earthquake window anomaly. ③ The variation of borehole strain anomaly in Xiaoshan, Haiyuan is related to Guyuan M 4.6 earthquake, and is in good agreement with the research results of prediction index of this item, but the magnitude of this earthquake is larger than the predicted magnitude. ④ Three moderate-strong earthquakes occurred during the period of abnormal development of Guyuan geo-resistivity and Guyuan geomagnetic harmonic amplitude ratio. From May 17 to 20, 2017, the EW of Guyuan georesistivity declined rapidly and then changed to a low value. The curve of Guyuan geomagnetic harmonic amplitude ratio NS to different periods has experienced a decline-turn-rise since 2014. Cheng has good seismic reflection efficiency.