重力异常反映的郯庐带中南段构造边界与应力场

Tectonic Boundary and Stress Field in the Middle-Southern Segment of Tan-Lu Fault Zone as Reflected by Gravity Anomaly

为解决传统基于重力场数据一阶导数定义的总水平导数和解析信号振幅存在无法均衡深浅异常振幅的问题,应用重力全张量梯度数据,提出改进的倾斜导数地质体边界识别方法NTD_(M)。经模型验证,NTD_(M)在收敛性、抑噪性和边界识别精度方面均有提升。利用NTD_(M)将郯庐带中南段及邻区划分为14个边界较为清晰的构造单元,借助垂线偏差数据对郯庐带中南段的构造应力场和壳幔密度差进行反演。结果显示,二者在水平方向上存在显著差异,在空间上显著相关,构造应力最大差异值约为16 MPa,壳幔密度差约为0.2 g/cm^(3),构造应力等值线密集处与构造单元划分的边界以及地震分布情况对应较好。郯庐带中段最大主应力方向为NEE-EW,南段主应力方向以EW-NWW为主,总体呈EW向,与震源机制解、地应力测量和GPS反演结果具有较好的一致性。

The total horizontal derivative and the amplitude of analytic signal defined by the first derivative of gravity field data cannot balance the amplitude of shallow and deep anomalies.Inorder to solve this problem,we propose an improved boundary identification method of inclined derivative geological body using gravity full tensor gradient data called NTD_(M).The NTD_(M) shows improvement in the convergence,noise suppression and boundary resolution of the new method.We obtain fourteen structural units with clear boundaries and use NTD_(M) for the gravity data in the middle-southern segment of Tan-Lu fault zone.Then,using gravity vertical deviation data,we inverse the tectonic stress field,crust-mantle density difference.The results show that there are significant differences in horizontal direction and spatial correlation.The maximum difference of tectonic stress is about 16 MPa,and the crust-mantle density difference is about 0.2 g/cm^(3).The dense area of tectonic stress isolines corresponds well to the boundary of structural unit and seismic distribution.The direction of the maximum stress of the middle part of Tan-Lu fault zone is NEE-EW and the southern part is EW-NWW,and the overall direction is EW.The results are in good agreement with those obtained based on focal mechanism solution,in-situ stress measurement and GPS inversion.