拜城及其邻区地震震源机制解与现今应力场特征

Solution of Seismogenic Mechanism and Stress Field Characteristics of Recent Earthquakes in Baicheng Area

摘要:

近年来拜城及其邻区发生过 M_S5.6、 M_S5.4、 M_S5.1 地震及多次有感地震,因此有必要对这些地震的震源破裂展开分析,探究南天山现今构造应力场分布特征。本研究首先收集了GCMT给出的1995—2021年拜城及其邻区M_S≥5.0中强地震的震源机制解结果,其次利用新疆台网2003—2024年宽频带波形数据,采用CAP方法补充计算了研究区M_S≥3.0地震的震源机制解,然后采用区域应力张量阻尼方法 (MSATSI) 反演南天山应力空间分布,最后探讨其应力场演化特征。结果表明,拜城及其邻区地震事件震源机制解以逆断型为主,库车坳陷地区地震深度集中在11km左右,昭苏盆地地区地震震源深度分布在10～25km范围内,震源深度上的差异是由发震断裂所处构造单元不同所引起的。拜城 M_S5.6 地震节面Ⅰ走向263°,倾角49°,滑动角98°; 节面Ⅱ走向71°,倾角42°,滑动角81°; 矩震级为M_W5.28,矩心深度为11km。区域构造应力场以压应力为主,且主压应力轴优势方向为近NS方向,与该地区1991—2016年GPS速度场方向相一致,应力形因子R值接近1,区域应力场以压应力为主。

Abstract:

In recent years,Baicheng and its neighboring regions have experienced several significant earthquakes,including events with magnitudes of M_S5.6, M_S5.4,and M_S5.1,as well as numerous perceptible seismic events. Given the seismic activity in this area,it is essential to analyze the source rupture processes of these earthquakes and investigate the distribution characteristics of the contemporary tectonic stress field in the southern Tianshan Mountains. This study undertakes a comprehensive analysis by first compiling focal mechanism solutions for strong earthquakes (M_S≥5.0) in Baicheng and its neighboring areas from 1995 to 2021,as provided by the Global Centroid Moment Tensor (GCMT) catalog. Subsequently,utilizing broadband waveform data from the Xinjiang Seismic Network spanning 2003 to 2024,the CAP (Cut and Paste) method is employed to supplement the calculation of focal mechanism solutions for earthquakes with M_S≥3.0 within the study region. The regional stress tensor inversion method (MSATSI) is then applied to invert the spatial distribution of stress in the southern Tianshan Mountains,and the evolution characteristics of the stress field are explored. The results indicate that the focal mechanism solutions for earthquake events in Baicheng and its neighboring areas are predominantly of the reverse fault type. In the Kuqa Depression area,earthquake depths are concentrated around 11km,while in the Zhaosu Basin area,focal depths range from 10km to 25km. These differences in focal depth are attributed to the distinct structural units of the seismogenic faults. The largest earthquake in the study area was the Baicheng M_S5.6 event,with the following focal mechanism parameters:for nodal plane I,the strike,dip,and rake are 263°,49°,and 98°,respectively;for nodal plane Ⅱ,these values are 71°,42°,and 81°. The moment magnitude (M_W) of this event is 5.28,and the depth of the moment center is 11km. The regional tectonic stress field is characterized by a dominant compressive stress regime,with the principal compressive stress axis oriented nearly in the north-south (NS) direction. This orientation is consistent with the GPS velocity field direction in the region from 1991 to 2016. The stress form factor R value is close to 1,indicating that the regional stress field is primarily compressive.