贵州西部多流域水库区地壳三维速度结构

3D Crustal Velocity Structure of Reservoir Areas in the Multiple River Basins of Western Guizhou Province

摘要:

使用基于机器学习构建的贵州西部多流域水库区地震目录和震相报告,采用波速比一致性约束的双差层析成像方法联合反演得到了该地区的地震位置和三维v_p、v_s、v_p/v_s结构。结果显示,研究区内的地壳速度结构具有明显的不均匀性,不同大地构造变形分区展现出不同的速度结构特征。在10km以上深度,横穿黔西中部NW向的威宁构造变形区显示出显著的低速异常条带,揭示了威宁—水城深大断裂带的影响深度和范围。受库区岩性和流体渗透的影响,0km深度的速度结构显示普遍的低波速和高波速比特征,包括夹岩、平寨、光照和马马崖水库区域。重定位后,地震的空间分布勾勒出大量隐伏断层的几何展布特征,结合三维速度结构,推测该区域的地震活动与水库周围的断层活化有关。

Abstract:

In this paper,we applied the v_p/v_s model consistency-constrained double-difference seismic tomography method with the earthquake catalogue and phase report constructed by machine learning and t,to obtain the seismic location and 3D v_p,v_s,v_p/v_s structures in the reservoir areas of western Guizhou Province. The results show that the velocity structures in the study area are of obvious heterogeneity,and different tectonic deformation zones show different velocity structure characteristics. At the depth of less than 10km,the NW-trending Weining tectonic deformation zone that crosses the central part of western Guizhou Province shows significant low-velocity anomaly bands,revealing the depth and range of the influence of the Weining-Shuicheng fault zone. Due to the influence of lithology and fluid permeability,the velocity structures at 0km depth in the reservoir area generally show the characteristics of low-velocity and high v_p/v_s, including Jiayan,Pingzhai,Guangzhao and Mamaya reservoir areas. The spatial distribution of relocated earthquakes provides the evidence of the geometric distribution characteristics of a large number of buried faults. Combined with the 3D velocity structure,it is inferred that the seismic activity in this area is related to the fault activation around the reservoir.