汾渭地堑岩石圈的应力场数值模拟与分析

Numerical simulation and analysis of lithospheric stress field in Fenwei graben

汾渭地堑系位于秦岭造山带以北,鄂尔多斯地块以东,是我国东部重要的一个强震活动带,构造活动十分密集.目前关于汾渭地堑的研究主要集中于其成因机制与构造演化历史、活动构造分布及地震统计、有限元数值模拟等方面.其中地震地质相关的研究主要覆盖了沉积层和地表断层层面,地球物理研究则主要关注地球的深部结构问题,整体而言较少涉及到浅部断层与岩石圈深部结构对于区域应力场的综合影响,在"深浅结合"方面仍有进一步研究的空间.本文在前人工作的基础上对研究区的地质背景进行了总结与研究,并且基于Crust 1.0地球物理数据库,结合板块运动、岩石圈结构以及区域内断层分布等各方面情况构建了三维分层黏弹性有限元数值模型,用以计算汾渭地堑岩石圈应力场分布特征.其中模型计算所得的位移场与最大水平主压应力方向与实际数据均吻合较好,本文采用最大差应力指标(σ_(1)-σ_(3))来衡量区域应力集中的程度.综合上述计算分析,我们得出了以下结论:(1)板块运动、岩石圈结构控制整体的构造应力场;(2)断层,尤其是活断层对局部应力场分布同样具有显著而重要的影响;(3)研究区构造应力场特征呈"不对称哑铃状",并且最大差应力的空间分布与地震分布特征具有一致性.

The Fenwei graben system is located to the north of the Qinling orogenic belt and to the east of the Ordos block. It is a strong earthquake belt in eastern China, with dense tectonic activities. The current research on the Fenwei graben mainly focuses on its genetic mechanism and tectonic evolution history, active structure distribution, seismic statistics, and finite element numerical simulation. Among them, seismic geology-related research mainly covers sedimentary layers and surface faults, while geophysical research mainly focuses on the deep structure of the earth. Generally speaking, it rarely involves the comprehensive influence of shallow faults and deep lithospheric structure on the regional stress field, it’s necessary for further research in the “combination of depth and shallowness”. This paper summarizes and studies the geological background of the study area on the basis of previous work. Based on the Crust 1.0 geophysical database, a three-dimensional layered viscosity model is constructed in combination with plate motion, lithospheric structure, and fault distribution in the region. The elastic finite element numerical model is used to calculate the lithospheric stress field distribution characteristics of the Fenwei graben. The displacement field calculated by the model and the direction of the maximum horizontal principal compressive stress are in good agreement with the actual data. This paper uses the maximum differential stress index(σ;-σ;) to measure the degree of regional stress concentration. Based on the above analysis, we have drawn the following conclusions:(1) Plate movement and lithospheric structure control the overall tectonic stress field;(2) Faults, especially active faults, also have a significant influence on the local stress field distribution;(3) The characteristics of the tectonic stress field in the study area are “asymmetric dumbbell-shaped”, and the spatial distribution of the maximum differential stress is consistent with the seismic distribution characteristics.