采用2021年青海玛多地震序列震源机制节面聚类确定发震断裂几何形态

Fault geometry determination by clustering nodal planes of focal mechanisms of the 2021 Maduo, Qinghai earthquake sequence

摘要:

地震断裂带形状是活动构造和地球动力学的重要资料。2021年发生的玛多地震序列提供了丰富的震源机制资料,为统计震源机制节面并估计玛多地震发震断层面形状提供了很好机会。文章对地震的震源机制资料进行基于密度的聚类来确定断层的几何形态。首先对收集到的玛多地震序列的震源机制解进行中心解求解，从而获得更为精准的数据,然后对其进行DBSCAN方法的聚类分析，得到断层的走向为113.5°，倾角为88.2°,通过震源机制反演应力场,并将应力场投影到断层上，得到断裂带的相对剪应力和相对正应力分别为0.84和-0.79,剪应力强度较大,滑动角为-0.72°。结果表明玛多地震是发震断裂受NE-SW的挤压和NW-SE的拉张,形成了较大的剪切力,从而促使近东西的江错断裂发生左旋走滑错动所致。

Abstract:

The shape of seismic fault zones is essential for the study of active tectonics and geodynamics. The Maduo earthquake sequence that occurred in 2021 provides rich focal mechanism data and a suitable opportunity for counting the nodal planes of focal mechanisms and estimating the geometry of the seismogenic fault. Herein, the seismogenic fault geometry was determined using a density-based clustering algorithm to analyze the focal mechanism data. First, the central focal mechanism of the Maduo earthquake sequence was solved to obtain accurate data. Then, the results of a strike of 113.5° and a dip of 88.2° were obtained using the DBSCAN method. Finally, by inversion and projection of the stress field on the fault, the relative shear stress and relative normal stress were obtained as 0.84 and -0.79, respectively, and the sliding angle was estimated as -0.72°. The results show that the Maduo earthquake was caused by the stress of northeast-southwest compression and northwest-southeast extension. Then, a large shear stress was generated on the Jiangcuo fault with a nearly east-west orientation, thus causing a left-lateral strike-slip dislocation on the fault.