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2016年9月23日,在四川西部理塘县相继发生M4.9和M5.1地震,震中位于青藏高原东缘川滇块体西北部金沙江断裂带与理塘断裂带所夹持的区域。文中基于四川区域地震台网提供的震相报告和波形资料,采用多阶段定位方法,对理塘M4.9和M5.1主震及余震序列进行了重新定位。同时,利用CAP波形反演方法,获得了这2个主震的震源机制解、震源矩心深度与矩震级。根据重定位后的余震空间分布形态、M4.9和M5.1主震的震源机制解,结合等震线形态及震中附近主要构造的展布,分析认为,近EW走向、倾向N的哈嘎拉断裂带为理塘M4.9和M5.1地震的发震构造,与该断裂带走向和倾向一致的节面Ⅰ为同震断层面,断面倾角44°。理塘M4.9和M5.1地震可能是在西侧羌塘块体物质持续E向挤入作用下、位于理塘—巴塘地区上地壳内的近EW向哈嘎拉断裂张性运动所致。
On September 23, 2016, M4.9 and M5.1 earthquakes occurred successively in Litang County, western Sichuan. The epicenter was located in the area sandwiched by the Jinshajiang fault zone and the Litang fault zone in the northwestern part of the Sichuan-Yunnan block in the eastern margin of the Qinghai-Tibet Plateau . Based on seismic phase reports and waveform data provided by Sichuan Regional Seismograph Network, the multi-stage localization method is used to re-locate the main shock and aftershock sequences of Litang M4.9 and M5.1. At the same time, using the CAP waveform inversion method, the focal mechanism solutions, focal depth and moment magnitude of the two main earthquakes are obtained. According to the spatial distribution patterns of aftershocks after relocating, the focal mechanism solutions of M4.9 and M5.1 main shocks, combined with the isoseismic patterns and the distribution of the main structures near the epicenter, suggest that the near-EW strike, The fault zone is the seismogenic structure of the Litang M4.9 and M5.1 earthquakes. The section I, which is consistent with the strike and dip of the fault zone, is a coseismic fault with a dip angle of 44 °. The Litang M4.9 and M5.1 earthquakes may be caused by the continual E-direction intrusion of Qiangtang block in the west of the Litang-Batang area, To