华北地区实测应力特征与断层稳定性分析

Analysis of characteristics of measured stress and stability of faults in North China

以中国大陆地壳应力环境基础数据库为基础,选取华北地区水压致裂法与应力解除法的实测地应力数据共计1 017条,得到华北地区及研究子区宏观应力场特征:(1)华北地壳浅层最大水平应力H、最小水平应力h随深度D呈线性增加;(2)在0~4 000 m测量深度范围内,华北各研究子区中间深度H值总体表现出"东高西低"的特征;(3)华北地区侧压系数Kav=225/D+0.61,浅部离散,随着深度增加而集中,并趋向0.61,D=577 m时Kav=1,是水平作用为主导向垂直作用为主导转换的"临界深度";(4)华北各研究子区H的优势方向统计显示,华北东部研究区H优势方向基本上为近EW、NEE、NE向。鄂尔多斯块体及环鄂尔多斯的研究区H优势方向呈现出NE向或NEE向。华北平原的研究区H优势方向主要为NE、NEE向,部分研究区呈现出NW向。分析华北区域断层稳定性发现,500 m深度以下实测差应力值不超过理论临界值,区域内断层基本上处于相对稳定的状态;0~500 m深度之间部分差应力值已达到或接近走滑临界状态,在方位合适的断裂或节理面上发生走滑断层型活动的可能性较大。

The hydraulic fracturing and stress relief measurement data of North China was collected mainly from 'Fundamental database of crustal stress environment in continental China'.The entries of in situ stress data are 1 017.The characteristics of macroscopic stress field in North China and study regions are investigated.The results are as follows:(1) The maximum horizontal stress H and minimum horizontal stress h all increase linearly with depth.(2) The intermediate regression value of(at 2 000 m depth) is various in study regions;and the basic characteristic of magnitude is high in east and weak in west.(3) The range of the lateral pressure coefficient Kav =225/D+0.61 with depth is: 15/D+0.42≤Kav ≤1 030/D+0.76.The distribution of Kav is scattered in superficial crust,becomes more concentrated in the deeper crust and trends to 0.61.At a critical depth of 577 m Kav equals to 1 which indicates the transition from horizontal to vertical stress domination.(4) The predominant directions of H are nearly E-W,NEE-SWW and NE-SW in east regions of North China.The directions of in study regions in and around Ordos block are mainly NE-SW and NEE-SWW.In study regions of North China Plain,the H directions are dominantly shown as NE-SW;and NNW-SSE,and some directions are NW-SE.Fault stability in North China are investigated: The stress difference at depths bellow 500 m has not reached the critical value of fault activity;and stress difference at depth above 500 m has reached or exceeded the sliding friction threshold of the strike-slip fault.