2023年甘肃积石山MS6.2地震发震断层产状及其动力学探讨

Seismogenic Fault Occurrence and Geodynamic Discussion of the 2023 Jishishan MS6.2 Earthquake,Gansu,China

摘要:

大地震发生后,断层面产状的迅速确定对地震破裂时空分布模型研究、发震构造及震后地震发生发展趋势判定具有重要参考价值。本文收集2023年甘肃积石山M_S6.2地震序列的震源机制解数据,将全部震源机制节面组合在一起进行模糊聚类分析,去掉小于设定阈值的噪声节面,得到两类聚类结果,发现两组聚类结果中,走向312.13°、倾角56.09°的第一类中心节面的聚类标准差较小,为发震断层面。然后,通过应力场与断层面关系确认发震断层面。根据本次积石山地震序列的断层面解求解了该地区的应力场,结果表明该地区受到青藏高原的EN向推挤,形成了SW-NE向挤压和SE-NW向拉张的状态,表示主应力大小的应力形因子R值较大,解释了该地区呈现逆冲兼走滑的震源机制地震占优势的原因。将求解得到的构造应力场分别作用到聚类得到的两类节面上求解断层面的剪应力,发现标准差较小的第一类中心节面处于剪应力较大区域。综合其他资料分析,本研究推测2023年甘肃积石山M_S6.2地震发震断层为NE倾向,走向为312.13°,倾角为56.09°。

Abstract:

The rapid determination of the seismogenic fault occurrence following a large earthquake is crucial for constructing seismic rupture models,understanding seismogenic structures,and estimating post-earthquake seismic activity. In this study,focal mechanism data from the 2023 Jishishan M_S6.2 earthquake sequence in Gansu,China,were collected and analyzed through nodal plane clustering. After removing noise points above the threshold,two clusters were identified. The cluster with a strike of 312.13° and a dip of 56.09° exhibited a smaller standard deviation and is considered the likely seismogenic fault occurrence of the M_S6.2 earthquake. To further verify this potential fault,the relationship between the fault occurrence and the stress field was analyzed. The stress field in the source region,derived from the focal mechanisms of this earthquake sequence,reveals NE-SW compression and NW-SE extension due to the pushing of the Tibetan Plateau. The high stress ratio is attributed to the dominance of thrust with a strike-slip component in the focal mechanisms. When the stress field was projected onto the two nodal plane centroids from the clustering analysis,it was found that the cluster with the smaller standard error experienced larger shear stress,with normal stress also supporting its rupture. Based on this comprehensive analysis,we conclude that the seismogenic fault of the 2023 Jishishan M_S6.2 earthquake is a north-west dipping fault with a low dip angle,having a strike of 312.13° and a dip of 56.09°.