青海共和盆地地应力状态与断层稳定性分析

The State of the In-situ Stress and Fault Slide Evaluation of Gonghe Basin,Qinghai Provice

青海共和盆地地质构造条件复杂,断层十分发育,区域内既有地热、太阳能、矿产等资源丰富,存在龙羊峡水库诱发地震环境背景。因此,分析青海共和盆地地应力特征与地质结构易滑性对于青海东部地区防震减灾具有重要意义。对盆地及附近区域内19个钻孔、65条水压致裂数据和44条应力解除实测数据进行统计分析,并基于断层摩擦强度理论、Byerlee-Anderson理论等断层力学相关理论讨论了研究区域断层易滑性与地震危险性。研究结果表明:研究区域内应力状态在深度350 m左右由逆冲型转换为走滑型,与区域内分布北北西右旋高角度逆断层相吻合;区域内最大水平主应力优势方位为N45°~E60°;地应力场初步结果反演表明研究区域应力场以逆冲型为主,局部地区兼走滑特征,与震源机制解反演结果一致;区域内断层平均摩擦系数为0.41,断层处于稳定状态,即断层易滑性较低,侧压力系数与应力积累指标插值分析结果同样表明断层整体易滑性较低,局部浅部断层带应力积累水平较高,综合分析推测断层易沿NW-SE向滑动。

The Gonghe Basin has complex geological structural conditions,well-developed faults,abundant geothermal,solar,and mineral resources in the area,as well as the Longyangxia Reservoir-induced earthquake environment background.Therefore,analyzing the characteristics of the in-situ stress and the slidability of the geological structure in the region is very important for earthquake prevention and disaster reduction in the eastern part of Qinghai.Based on the analysis of 65 hydraulic fracturing data and 44 stress relief measured data from 19 boreholes in the basin and nearby areas,and based on the theory of fault friction strength,Byerlee-Anderson theory and other related fault mechanics theories,the fault slidability and seismic risk of the study area are discussed.The results show that the stress state in the study area changes from thrust to strike-slip stress state at a depth of about 350 m,which is consistent with the north-north-west right-lateral high-angle reverse faults in the area;The dominant position of the maximum horizontal principal stress in the area is N45°~E60°;The preliminary inversion of the in-situ stress field also shows that the stress field in the study area is dominated by thrusting,and the local area is also characterized by strike-slip,which is consistent with the inversion result of the focal mechanism solution;The average friction coefficient of the fault in the area is 0.41,and the fault is in a stable state,that is,the fault is relatively slippery;At the same time,the results of interpolation analysis of the lateral pressure coefficient and the stress accumulation index found that the overall slidability of faults in the Gonghe Basin is low,and the level of stress accumulation in local shallow fault zones is high.Comprehensive analysis predicts that it is easy to slide along the NW-SE direction.