2014年三峡秭归M4.5、M4.7震群序列定位及震源区三维P波速度结构研究

Relocation of the 2014 Zigui, Sanxia M4.5, M4.7 Earthquake Swarm and 3D P-wave Velocity Structure in the Source Region

摘要:

采用双差层析成像方法，对2014年3月27日M4.7和3月30日M4.5秭归震群重定位显示：0~5 km深度层P波高速区分布在仙女山断裂北中段和九畹溪断裂北段，天阳坪断裂一带为低速区；8 km深度层高速区分布在九畹溪断裂东侧，仙女山断裂较低；11 km层高速区仅分布在高桥断裂和周家山—牛口断裂之间地带。在地震集中区的下方（即8~12 km处）存在分布较为稳定的低速区，较大地震事件主要分布在高速区或高低速区交界地带，低速区内则很少有地震分布。局部高速体的存在为岩石发生瞬间破裂提供了物质基础，其与低速体间的梯度带是发震构造常发育的区域。研究区内的仙女山断裂北段、九畹溪断裂正是在该梯度带内发育的两条活动断裂。本地震序列的自地表至5 km和5~10 km深度范围内均有大量破裂存在表明，浅层地震仍在水库渗透范围内，而深部地震则与流体渗透无关。此次地震活动同时存在水库诱发地震和构造地震存在。

Abstract:

In this paper, the double-difference tomography method was used to relocate the Zigui, Sanxia M4.7 earthquake swarm on March 27 and M4.5 earthquake swarm on March 30, 2014. The inversion results showed that at depths of 0-5 km, the high-velocity zones of P-wave are mainly distributed in the northern and middle sections of Xiannushan fault and the north section of Jiuwanxi fault, and the low-velocity zones are mainly distributed along the Tianyangping fault; the high-velocity zones at depth of 8 km are distributed in the east side of Jiuwanxi fault; the high-velocity anomalies at depth of 11 km are only distributed in the junction zone of Gaoqiao fault and Zhoujiashan-Niukou fault. The low-velocity zone below the earthquake concentration area (8-12 km) is relatively stable. Large earthquake events are mainly distributed in high-velocity zones or high-low velocity junction zone, while few earthquakes are distributed in the low-velocity zone. Local high-velocity body provides the material basis for instantaneous fracture of rocks, and the gradient zone between it and the low-velocity body often develops seismogenic structures. A large number of fractures exist in the depth range from the surface to 5 km and 5-10 km, indicating that shallow earthquakes are still in the range of reservoir permeability, while deep earthquakes are irrelevant to fluid permeability. There are both reservoir-induced earthquakes and tectonic earthquakes in the earthquake swarm.