2017年8月9日精河MS6.6地震余震序列精定位及发震构造分析

Precise location and seismogenic structure analysis of aftershock sequence of Jinghe MS6.6 earthquake on August 9,2017

  • 摘要: 为确定2017年8月9日精河MS6.6地震的发震构造,本文使用双差定位方法对发震时刻至2017年10月震源区所发生的余震进行了精定位,同时利用CAP波形反演方法,得到了主震的震源机制解,同时使用GPAT方法反演得到了部分余震的震源机制解,并基于两者对本次地震的发震构造予以分析。结果显示:精定位后主震位于(44.27°N,82.85°E),震源深度为17 km;主震最佳双力偶解对应的节面Ⅰ的走向为260°、倾角为51°、滑动角为84°,节面Ⅱ的走向为89.5°、倾角为39.4°、滑动角为97.4°;余震序列位于主震东侧,并向东展布约30 km,在3—18 km深度范围内均有分布,其优势方向为近EW向,次优势方向为SW向。结果表明,本次地震是一次逆冲型地震,通过反演得到的大量小震震源机制解的结果与主震震源机制解结果相一致。结合余震震中分布、主震及余震的震源机制解以及震源区的地质构造,本文推断近EW走向具有逆冲性质的库松木楔克山前断裂为精河主震的发震构造。

     

    Abstract: On August 9, 2017, an earthquake with MS6.6 occurred in the Jinghe of Bortala Mongolia Autonomous Prefecture, Xinjiang, and the highest intensity is estimated up to Ⅷ, but no major surface ruptures had been observed in field survey. In order to determine the seismogenic structure of the Jinghe earthquake, this paper precisely locates the aftershocks occurred from the origin time of the main shock to December of 2017 in the source region by the double-difference location method. At the same time, the focal mechanism of the main shock is obtained by using the CAP waveform inversion method, and the focal mechanisms of some aftershocks are obtained by using the generalized polarization amplitude technology. The results show that the main shock is located at (44.27°N, 82.85°E) and the focal depth is 17 km. The aftershock sequence is located to the east of the main shock with focal depth of 33−18 km and an extending length nearly 30 km towards east. The predominant direction of the sequence is EW direction, and the subdominant direction is SW direction. The best double-couple solution of the main shock has one nodal plane with strike 260°, dip 51°, rake 84°, and the other nodal plane with strike 89.5°, dip 39.4°, rake 97.4°. The result suggests that the Jinghe earthquake is of thrusting type, and the focal mechanisms of a large number of small earthquakes obtained by inversion are consistent with that of the main shock. Combined with aftershock epicenters, focal mechanism solutions for the main shock and the aftershocks, as well as geological structure of the source region, it is inferred that the thrusted Kusongmuxieke piedmont fault extending in near EW direction is the seismogenic structure for the Jinghe main shock.

     

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