南汀河西支断裂深浅构造特征——来自深地震反射剖面的证据

云南省西南部,发育一组由不同断裂组成的北东向断裂构造带,沿这些断裂数十年来相继发生过多次强震.本文以其中的南汀河西支断裂为研究对象,采用深地震反射剖面方法,获得了断裂及两侧地壳精细结构和构造图像.探测结果表明:研究区纵向上,分为上、下两层地壳结构,总厚度约为31.25~35.6 km;横向上,以南汀河西支断裂为界,两侧反射特征差异较大,分别以弧状或倾斜反射波组为主·测线经过地区,莫霍面反射特征较为清晰,为2-3个反射同相轴组成的反射条带.南汀河西支断裂为一个由5条分支断层组成的断裂带,呈花状结构,反映了一种走滑挤压的应力状态.断裂带下方,存在一条切穿下地壳及莫霍面并延伸至上地幔的深大断裂·这种深、浅断裂共存的构造格局是控制南汀河地区地震孕育和发生的重要因素之一.

Shallow and deep structural characteristics of the west branch of the Nantinghe fault:evidence from deep seismic reflection profiling

Sourthwestern Yunnan Province hosts a NE-trending fault zone consisting of many faults,on which several major earthquakes have taken place successively in past decades.This work focused on the west branch of Nantinghe fault zone. Using deep seismic reflection profiling, we have imaged fine crustal structures and tectonics beneath the fault and either side of it. The results show that the crust of this area is 31.25~35.6 km thick,comprisings two layers. On either side of the west branch of Nantinghe fault, reflection features diffent much,dominated by arc-like and tilting reflective wave sets,respectively.Along the profile,the Moho interface can be identified by reflective strips made up of 2 or 3 reflection events. The west branch of the fault zone is composed of 5 faults that exhibit a flower structure indicative of a stress state of strike-slip and compression. Beneath the fault zone, there is a deep fault cutting low crust and the Moho and extending downward to upper mantle.Such a coexistence structural pattern of shallow and deep faults is one of the factors to control seismicity in the Nantinghe area.