鄂尔多斯地块南缘地应力测量研究

利用水压致裂法得到的地应力测试数据对鄂尔多斯地块南缘地壳浅部地应力分布规律及断层活动性进行研究。结果表明:(1)两个水平主应力随深度线性增长,应力梯度分别为0.032和0.021,在测量深度域内水平和垂直应力的关系为S_HS_hS_V,该应力状态有利于断层发生逆断层活动,与1556年华山大地震的发震正断层的性质不同;(2)研究区的最大水平主应力方向为北南—北北西向,与区域速度矢量场方向一致,与其他资料解译的区域构造应力方向有一些差异,主要是受鄂尔多斯地块周缘断层活动的影响;(3)利用Mohr-Coulomb准则及Byerlee定律,摩擦系数取0.6~1.0,对研究区的地应力状态进行分析,发现鄂尔多斯地块南缘的测点未达到或超过地壳破裂极限状态,不存在断层失稳或地震等其他形式的地壳活动,处于较稳定地壳应力状态;(4)实测数据为该区补充了新的地应力测量资料,研究结果为该区工程设计及建设、构造应力场数值模拟提供了边界条件,对于该区地质灾害评价、地壳稳定性以及大陆动力学的研究具有重要意义。

IN-SITU MEASUREMENTS IN THE SOUTHERN MARGIN OF THE ORDOS BLOCK

The crustal stress distribution pattern and fault activity of the shallow crust in the southern margin of the Ordos block are studied by using the stress test data obtained from hydraulic fracturing method. The results reveal that the maximum and minimum horizontal principal stress show a good linear relationship with depth. The gradient is 0.032 and 0.021, respectively. Stress structure of S_H > S_h > S_V is favorable for the activity of the reverse fault and that is different from the normal fault occurred in the 1556 Huashan earthquake. The direction of the maximum horizontal principal stress is NS-NNW, which is consistent with the direction of velocity vector field. It is different from regional tectonic stress direction interpreted by other data, which may be affected by the fault activity around the Ordos block. The crustal activity in the study area is discussed by using the Mohr-Coulomb criterion and Byerlee''s law under the premise that the friction coefficient is 0.6~1.0. We found that the measured points in the southern margin of Ordos block have not reached or exceeded the limit of the earth''s crust rupture and there are no fault instability or earthquake and other forms of the activities, which is in a relatively stable state of crustal stress. New in-situ stress measurement data have been added to the area. The research results provide the boundary conditions for the engineering design and construction, numerical simulation of tectonic stress field in the area, which is of great significance for the study of geological hazard assessment, crustal stability and continental dynamics.