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对由四川台网提供的2008年5月12日至2008年12月31日期间发生的地震观测报告资料进行了整理,并根据研究需要从中挑选出了2957次地震事件用于地震定位研究。然后,采用双差定位方法对汶川M_s8.0级地震及挑选出的余震进行了重新定位,得到2678个地震的震源位置,重新定位后走时均方根残差由重新定位前的1.01s降到了0.20s,水平和垂直方向标准差分别为±0.85km和±1.3km。余震震中沿走向分布的总长度约为350km,震源深度优势分布为5～20km,平均震源深度为11.4km。文章结合地表考察破裂、震源机制解等研究结果,对余震空间分布进行了更为详细的分段和讨论,提出以下3点认识:1)余震震中沿主破裂带表现出明显的空间分段活动特征,根据余震空间分布特征和震源机制解可推测断层运动方式由一开始的逆冲为主,经过渡段最终转换为以右旋走滑为主;2)沿小鱼洞-棉篪-理县和青川-文县方向延伸的北西向余震带存在两个与龙门山构造带走向近似垂直的捩断层;3)龙门山构造带的北段(水观乡以北),存在一个斜跨北川-映秀断裂和青川-平武断裂的隐伏断层,并且该隐伏断层参与了北段余震的发震过程。
Seismic observation data from May 12, 2008 to December 31, 2008 provided by Sichuan Network were sorted out and 2957 earthquake events were selected for seismic location research according to the research needs. Then, the double-difference method was used to reposition the M_s8.0 Wenchuan earthquake and the selected aftershocks, and the focal locations of 2678 earthquakes were obtained. After relocation, the root-mean-square residual error decreased from 1.01s before repositioning 0.20s, the horizontal and vertical standard deviations are respectively ± 0.85km and ± 1.3km. The total length of the aftershocks distributed along the strike is about 350 km. The depth distribution of focal depths is 5 ~ 20 km and the average focal depth is 11.4 km. In this paper, the spatial distribution of aftershocks is discussed in detail in the light of the research results of surface rupture and focal mechanism solution. The following three points are put forward: 1) The aftershock epicenters show obvious spatial segmentation along the main rupture zone According to the spatial distribution characteristics of aftershocks and focal mechanism solutions, it can be inferred that the fault movement mode is mainly from the beginning of thrusting, and is mainly converted to dextral strike-slip after the transition; 2) There are two faults in the NW-trending aftershock extending along the Wenchuan-Wenxian County and the Qingchuan-Wenxian direction. There are two faults that are approximately perpendicular to the Longmen Shan tectonic belt. 3) There is a diagonal Beichuan Yingxiu fault and Qingchuan-Pingwu fault, and the buried fault is involved in the seismogenic process of aftershocks of the northern segment.