西藏芒康震群发震构造分析

2018年12月13日23时32分、39分,在西藏昌都市芒康县连续发生M 4.9和M 4.4地震;随后12月14日1时15分、38分、42分,该地又连续发生了3次M≥3.0地震,地震震中位于川滇菱形块体西北部金沙江断裂带、巴塘断裂带和藏东澜沧江断裂带所夹持的区域。基于四川及周边区域地震台网的观测资料,采用双差定位方法,对芒康震群序列进行了重新定位,并利用CAP波形反演方法,获得了5个M≥3.0地震的震源机制解、震源矩心深度与矩震级。根据震群序列空间展布、较大地震震源机制解和震源区附近的地质构造,初步分析认为:芒康震群序列地震展布在地表下长约16 km、宽约6 km,深度在5~20 km的区域;与震群序列空间展布方向较为一致的节面I为发震断层面,断面倾向NE,倾角约为65°,滑动角约为-34°;震源区主压应力P轴方位为近EW向,与该区域构造应力场主压应力方向一致,推测本次震群地震应是在羌塘块体物质持续E向挤入作用下,位于羌塘地块东南缘的一条NWW向次级隐伏断裂拉张运动引起的。

Analysis on the Seismogenic Structures of the Earthquake Swarm in Xizang Mangkang Region

At 23∶32 and 23∶39 on 13 December 2018,the M 4.9 and M 4.4 earthquakes happened successively in Mangkang County and Changdu city in Tibet.Whereafter,at 1∶15 and 1∶38 on 42 December 14,three M≥3.0 earthquakes happened successively in this area.These earthquakes epicenter was located among the Sichuan-Yunnan diamond block northwest Jinsha River fault zone,Batang fault zone and the Xizang eastern Lancang river fault zone.This paper is based on the observational data of the seismic networks in Sichuan and surrounding areas,using the double difference positioning method,the Mangkang earthquake group sequence was repositioned.Using the CAP waveform inversion method,we obtained the focal mechanism solutions,focal moment depths and moment magnitudes of the five M≥3.0 earthquakes.According to the spatial distribution of earthquake swarm sequence,the focal mechanism solution of these larger earthquakes and the geological structure near the focal area,preliminary analysis shows that:the distribution of the Mangkang earthquake swarm is about 16 km long,6 km wide and 5~20 km deep under the surface;The node plane I which is more consistent with the spatial distribution direction of the earthquake swarm sequenceis the seismogenic fault plane.The fault planes tend to NE,the dip Angle is about 65°,the sliding Angle is about-34°;The main compressive stress p-axis in the source area is near to EW.It is consistent with the main compressive stress direction of the tectonic stress of this region,Under E direction extruding of the Qiangtang block,it is speculated that this earthquake cluster is caused by the tensional movement of a NWW direction blind fault in the southeastern margin of the Qiangtang block.