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2015年四川乐山金口河M5.0地震孕震构造条件分析
宫悦, 龙锋, 梁明剑, 易桂喜, 王宇玺, 格桑扎西
四川省地震局, 成都 610041
摘要:
2015年1月14日乐山金口河M5.0地震发生在历史地震强度较低的川南山区与四川盆地交界一带。基于四川区域地震台网的震相报告与波形资料,采用双差定位法对地震序列进行重新定位,同时,采用CAP波形反演方法及HASH方法反演了主震及序列中8次ML≥2.0地震的震源机制解。另外,利用Coulomb3计算了主震发生后库仑应力改变量,得到的结果如下:①重新定位结果显示,金口河M5.0地震位于(103.18°E,29.32°N),震源深度16.6km,略深于波形反演结果(12km)。序列分布在NNW向天全-荥经断裂和NE向西河-美姑断裂的交汇部位,余震序列在空间上呈NE向展布。②M5.0主震的机制解为节面Ⅰ:走向350°/倾角46°/滑动角107°,节面Ⅱ:走向146°/倾角47°/滑动角73°,表现为走向NW(NNW)、中等倾角的逆冲型运动方式。序列中其余8次ML≥2.0余震大多以走向NE的逆冲型地震为主,个别为走滑或正断层类型。主震和大部分余震的节面方向不一致,主震节面方向与余震长轴方向也不一致。③主震后库仑应力改变量显示,余震主要发生在主震引起的库仑破裂应力增加的区域。综合分析推测,NNW向天全-荥经断裂为本次地震主震的发震构造,倾向NE的机制解节面Ⅰ指出了该断裂的几何产状;M5.0主震发生后,立即触发了其旁侧的NE向西河-美姑断裂,并激发了多次余震。
关键词:  金口河M5.0地震  双差定位  震源机制解  发震构造  库仑应力
DOI:
分类号:P315
基金项目:国家重点研发计划(2018YFC150330501)、2019年地震大形势项目(15230023)共同资助
Seismogenic Structure of the Jinkouhe MS5.0 Earthquake in 2015
Gong Yue, Long Feng, Liang Mingjian, Yi Guixi, Wang Yuxi, Gesangzhaxi
Sichuan Earthquake Agency, Chengdu 610041, China
Abstract:
On January 14,2015,the Jinkouhe MS5.0 earthquake occurred at the juncture of northern Sichuan and Sichuan Basin,where only several earthquakes had been recorded. Based on the digital waveform date and seismic phase report of Sichuan Regional Digital Seismic Network,the Jinkouhe earthquake sequence was relocated by double-difference method,and focal mechanisms of the sequence of 9 earthquakes with ML ≥ 2.0 were calculated by employing the CAP method and HASH method. The coulomb stress in the region was also calculated by coulomb3.The result indicates that:① The Jinkouhe MS5.0 earthquake was located at(103.18°E,29.32°N).The focal depth was about 16.6km,which was slightly deeper than the depth obtained using waveform inversion (12km). The aftershock sequence was evenly distributed in the intersection of NNW trending Tianquan-Yingjing fault and NE trending Xihe-Meigu fault,which were aligned tending to the NE directions. ② Focal mechanism solution result indicated that the ML ≥ 2.0 aftershocks were mainly dip-thrusting,the nodal plane parameters of the main event were as follows:nodal plane Ⅰ is strike=350°,dip=46°,rake=107°,and nodal plane Ⅱ was strike=146°,dip=47°,and rake=73°. ③ The result of coulomb stress indicated that the aftershocks mainly occurred in the area where the coulomb stress increased. According to comprehensive analysis,we inferred that the NNW-striking Tianquan-Yingjing fault was the seismogenic fault of the main shock,and the nodal plane Ⅰ of NE dip point out the occurrence of the fault,the M5.0 main shock immediately triggered the NE-directed Xihe-Meigu fault,and then triggered many aftershocks.
Key words:  The Jinkouhe MS5.0 earthquake  Double-difference method  Focal mechanism  Seismogenic structure  Coulomb stress