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Title:: Relocation of the 2018 Tonghai M_S5.0 Earthquakes Swarm,Yunnan and Velocity Imaging of the Source Region

Author(s):: WANG Yue; MENG Lingyuan; HAN Yanyan; MA Yawei; DENG Shiguang; (China Earthquake Networks Center,Beijing 100045,China)

Keywords:: Tonghai seismic swarm; double-difference location; relocated sequence; upper crustal velocity

摘要:: 利用2018年8月13日至12月31日云南通海M_S5.0震群震源区的观测报告,采用双差层析成像方法对通海M_S5.0震群序列重定位,获得了震源区附近上地壳的三维速度结构。结果表明:震源区速度结构呈现明显横向不均匀,在玉江断裂和小江断裂南段的明星—二街断裂交汇处,5 km深度上,震源区出现高速异常,延伸至10 km,而在15 km深度上,表现为低速异常。重定位后的震源位置精度明显得到提高,地震事件分布更加集中,震中位置呈NE—SW向条带状分布,2次主震空间相距约18 km,震源深度分布范围为3 ～ 12 km,8月13,14日2次M_S5.0地震的震源深度分别约为8.63 km,和9.16 km。综合分析震源区地震地质资料、速度结构成像结果及重定位后地震序列空间分布认为,位于小江断裂带南段,且与明星—二街断裂近乎平行的隐伏断裂可能是此次通海震群的发震构造。

Abstract:: In this study,we relocated the 2018 Yunnan Tonghai M_S5.0 earthquakes swarm and determined a 3D velocity model of the upper crust of source area using the double-difference seismic tomography method.All the seismic phase observation reports are provided by the China Earthquake Networks Center(CENC).The results show that the velocity structure of the epicenters of the Tonghai sequence present obvious lateral inhomogeneity.At the junction of the Yujiang fault and the Mingxing-erjie fault which was located in the south of Xiaojiang fault,and the velocity presents high values at the depth 5 km and till to the 10 km,while the velocity presents low values at the depth of 15 km.The well relocated epicenters of the Tonghai M_S5.0 earthquakes sequence exhibited in a narrow band along the NE-SE direction,the distance between two main events is approximately 18 km,and the predominant range of depth distribution is from 3 km to 12 km.The depths of the two main events occurred on 13 and 14 August are 8.63 km and 9.16 km,respectively.Based on the comprehensive results of the velocity structure of source area,the distribution of the relocated epicenters and hypocenters,and the geological structures,we infer that a pre-exist fault which is parallel to the Mingxing-erjie fault is the seismogenic fault of the Tonghai M_S5.0 seismic swarm.