2015年7月3日皮山6.5级地震发震构造初步研究

基于新疆区域数字地震台网记录，采用CAP（Cut and Paste）方法反演了2015年7月3日皮山6.5级主震和部分M_S3.6以上余震的震源机制解和震源深度；采用HypoDD方法重新定位了序列中M_L2.5以上地震序列的震源位置，并利用小震分布和区域应力场拟合了可能存在的发震断层面参数.基于上述研究，综合分析了皮山6.5级地震序列的震源深度、震源机制和震源破裂面特征，探讨可能的发震构造.结果显示，利用CAP方法得到的最佳双力偶机制解节面I：走向280°/倾角60°/滑动角90°；节面Ⅱ：走向100°/倾角30°/滑动角90°，矩心深度19 km，表明该地震为一次逆冲型地震事件.大部分M_S3.6以上余震震源机制与主震具有一定的相似性.双差定位结果显示，M_L2.5以上的余震序列主要分布在主震的西南方向，深度主要分布在0～15 km范围内，余震分布显示出与发震构造泽普隐伏断裂一致的倾向南西的特征.利用小震分布和区域应力场拟合得到发震断层参数为走向104°/倾角34°/滑动角94°，该结果与主震震源机制解中节面Ⅱ的滑动角较为接近，绝大多数余震发生在断层面附近10 km左右的区域.根据本研究得到的震源机制、精定位结果以及利用小震分布和区域应力场拟合得到的断层面的参数，结合震源区地质构造情况，初步给出了此次皮山6.5级地震的发震模式.

Preliminary study for seismogenic structure of the Pishan MS6.5 earthquake of July 3, 2015

Based on the digital waveforms of Xinjiang Seismic Network, the best double-couple focal mechanisms of the main shock and some aftershocks of M_S≥3.6 were determined by the CAP method, and the Pishan 6.5 earthquake sequence M_L≥2.5 was relocated by the HypoDD. The geometric parameters and slip direction of the fault were estimated by using distribution of the earthquake sequence and regional stress field. We analyzed the characteristics of focal depth, focal mechanisms and source rupture to determine the seismogenic structure. The nodal plane parameters of the best double-couple focal mechanism by the CAP method are strike 280°, dip 60ånd rake 90°, and strike 100°, dip 30° and rake 90°, respectively. The depth of the centriod is about 19 km, the focal mechanism of the main shock is pure thrust, and most of focal mechanisms of M_S≥3.6 aftershocks show the same rupture property as the main shock. The result of HypoDD shows that the aftershocks are mainly distributed in the southwest of the main shock, the focal depths are in a range 0~15 km, largely consistent with the seismogenic structure, i.e. the hidden Zepu fault dipping southwest. Using distribution of small earthquakes and the regional stress field, we determined the focal fault parameters as follows:strike 104°, dip 34° and rake 94°, close to the nodal plane Ⅱ of the main shock. Most aftershocks are distributed in the 10 km vicinity of the focal plane. According to the focal mechanism derived, precise positioning results and the parameters of the fault plane from distribution of small events and fitting the regional stress field, combined with the geological structure in the source region, a preliminary seismogenic model of the 6.5 earthquake is proposed.