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Title:: Research and Monitoring of the 2006 M5.1 Double Shocks in Yanjin,Yunnan,China

Author(s):: YE Jian-qing; CHEN Hui; LIU Xue-jun; GUO Zhi-hua; CAI Shao-ping; (Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)

Keywords:: near-field earthquake observation; rupture process; source parameter; double shocks; Yanjin of Yunnan

摘要:: 利用2006年云南省盐津两次5.1级地震现场流动台网的近场地震监测资料,结合云南区域地震台网地震波资料进行精确定位,给出了盐津地震主、余震的震源参数,并分析讨论了这两次地震的震源过程。结果显示,这两次地震处于同一构造区,发震构造为NE向断裂,主破裂走向约N53°E,倾向NW,倾角约80°,断层性质为走滑型。断层破裂长度约9 km,宽度约3 km,破裂面深度3～9 km,断层走向与宏观等震线长轴方向基本一致。震源参数研究表明,盐津震区地震矩为10⁹～10¹⁶ N·m,震源破裂半径为90～300 m,应力降为0.000 2～32 MPa。高应力降地震事件主要发生在5～10 km深度范围内,表明该深度区是盐津地震的主要活动区。定位结果还显示,第1次地震的破裂面在深度7～9 km之间为余震空白区,认为该空白区是盐津地震主破裂面上的障碍体,第2次地震将障碍体贯穿。地震破裂面障碍体的存在是盐津震区发生两次地震的主要成因,说明地震空白区图像对地震预测具有十分重要的意义。

Abstract:: Two M5.1 earthquakes occurred in Yanjin,Yunnan,China,in 2006.We located the events with high precision,solved the source parameters of the Yanjin earthquake sequences,and discussed the rupture processes of the Yanjin doublet by using the near-field and regional seismic waveforms.The result shows that the two M5.1 earthquakes lie in the same tectonic region.The main fracture at depth 3-9 km is strike slip with a dimension about 9 km×3 km approximately,a strike about N53°E,and a dip about 80°.The strike of the fracture is consistent with that of the long axis of isoseismals.The seismic moment,rupture radius and stress drop are 10⁹-10¹⁶ N·m,90-300 m and 0.000 2-32 MPa respectively in the seismic area.The events with higher stress drop concentrated at depth 5-10 km,so this depth range is the main active zone of the Yanjin earthquakes.The spatial distribution of the aftershocks displays that the main rupture plane of the former M5.1 earthquake has an absent-shock zone at depth 7-9 km,which is regarded as the asperity on main rupture plane,and the following M5.1 earthquake ruptured through the asperity.This suggests that the asperity on the rupture plane resulted in the Yanjin double shocks.So the absent-shock zone mapping is important for earthquake prediction.