2018年9月4日伽师5.5级地震序列震源机制解及震源处应力场特征

Focal Mechanism Solution for Jiashi Ms5.5 Earthquake Sequence on September 4,2018 and the Characteristics of Stress Field in the Source Area

本文采用新疆测震台网数字波形记录,利用CAP和P、S波初动和振幅比方法计算2018年9月4日伽师5.5级地震序列中MS≥2.5地震的震源机制解,结合地震烈度等震线和双差重定位后的地震序列空间展布等特征分析了此次地震的发震构造,反演了震源处应力场。结果表明,伽师5.5级地震呈NE向的节面I为发震断层面,属于左旋走滑断层,震源深度为9km,发震构造可能为浅部超基底断裂;地震序列中有21次为走滑型,4次为正断型,说明绝大多数序列的破裂方式与主震相近,表明余震应力场主要受主震震源应力场控制;P轴方位在NNE向有明显的优势分布且倾伏角较小,T轴方位在NWW向有明显的优势分布且倾伏角较小,说明震源处主要以NNE向水平挤压和NWW向水平拉张作用为主;此次伽师5.5级地震序列表现的浅部应力场与已有研究得出的震源区深部应力场基本一致,应力形因子R的最优解为0.17,说明震源处近NE向中间主应力σ2有一定挤压成分。

Based on the digital waveforms record of Xinjiang seismic network,the CAP and P-wave,S-wave initial motion and amplitude ratio methods were used to calculate the focal mechanism solution of the MS≥2.5 earthquake sequence of Jiashi Ms5.5 earthquake on September 4,2018.The seismogenic structure of this earthquake was analyzed based on the seismic intensity isoseismic lines and the spatial distribution of the earthquake sequence after double differential relocation,and the stress field in the source area was inverted.The results show that the nodal plane I is the seismogenic fault,which is northeast trend and nearly upright left-lateral strike slip fault.The focal depth of main shock is about 9km.It is preliminarily inferred that the seismogenic structure may be superficial ultra crystalline basement fault.The 21 earthquake sequences are strike-slip and 4 earthquake sequences are normal faults.The rupture pattern of most earthquake sequences is similar to that of the main shock,indicating that the aftershock stress field is mainly controlled by the main shock source area stress field.P axis is near north-northeast,and the inclination angle is small.T axis is near northwest-west,and the inclination angle is small.It indicates that the stress field of source area is mainly under action of north-northeast horizontal compression and the northwest-west horizontal tensional.The shallow stress field shown in Jiashi 5.5 earthquake sequences is basically the same as the deep stress field obtained from previous research.The stress shape ratio is 0.17,and it shows that there is a certain compression ofσ2.