地质学报2017，Vol.91Issue(5)：969-978,10.
芦山地震前后龙门山断裂带西南段地应力状态对比分析
Comparative Analysis of In-situ Stress State in the Southwestern Segment of Longmenshan Fault Zone before and after Lushan Earthquake
摘要
Abstract
Hydraulic fracturing and piezomagnetic overcoring in-situ stress measurements were carried out in two boreholes in the southwestern Longmenshan Fault Zone to understand the current in-situ stress state and stress change after the Lushan Ms 7.0 earthquake on the April 20th,2013.Measurement results show that the maximum horizontal principal stress and minimum horizontal principal stress at the Qiaoqi borehole is 19.60～25.83 MPa and 10.47～18.47 MPa within the depth of 128～188 m,with an orientation of N63°～85°W;the maximum horizontal principal stress and minimum horizontal principal stress at the Tianquan borehole is 8.21 ～ 9.31 MPa and 5.20 ～ 7.73 MPa within the depth range of 114 ～ 142m,with an orientation of N59°W.Relationships between horizontal stress and vertical stress of the two measuring points are σH＞σh＞σv.The average ratios of maximum and minimum horizontal stress to vertical stress at the Qiaoqi borehole are 5.27 and 3.01 respectively.The average ratios of maximum and minimum horizontal stress to vertical stress at the Tianquan borehole are 2.60 and 1.76 respectively.The results that horizontal stress is higher than vertical stress will lead to a reverse fault activity.Comparison of insite stress states in this area before and after the Lushan earthquake suggests that after the earthquake the accumulation of stress of the unbroken active faults on both sides of the epicenter has been increasing.What's more,the stress magnitude at the Qiaoqi borehole improves significantly after the earthquake,which is in consistent with the monitoring results at the Qiaoqi.On the basis of in-situ stress data and Coulomb faulting criterion,the maximum horizontal principal stress at Qiaoqi was between the minimum and the maximum of fault slip before the earthquake,and exceeded the maximum after the earthquake.The maximum horizontal principal stress at Feixianguan was lower than the maximum of fault slip before earthquake.μm,the ratio between the maximum horizontal principal stress [(σ1-σ3)/2] and average stress [(σ1+σ3)/2],can be used to evaluate the present stress accumulation level and the seismic risk.The pre-earthquake μm value at Qiaoqi was 0.16～0.72,with an average of 0.50,and the post-earthquake μm value at Qiaoqi is 0.71 ～ 0.81,with an average value of 0.77.The pre-earthquake μm value at Feixianguan was 0.31～0.35,with an average of 0.32,and the post-earthquake μm value at Tianquan was 0.53～0.57,with an average value of 0.55.μmvalues in two study areas show a big difference.This study concludes that the stress in the northern and southern segments of the Longshan fault zone has been accumulated,which can increase possibility of fault slipping,especially in the northern segment.关键词
芦山地震/龙门山断裂带西南段/地应力测量/地应力变化/断层滑动Key words
the Lushan earthquake/southwestern segment of Longmenshan fault zone/in situ stress measurement/change of in situ stress/fault slip引用本文复制引用
邱君,吴满路,范桃园,张重远,李冉,陈利忠..芦山地震前后龙门山断裂带西南段地应力状态对比分析[J].地质学报,2017,91(5):969-978,10.基金项目
本文为中国地质调查局项目(编号12120114002101)资助的成果. （编号12120114002101）
