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

作　　者：邱君[1,2] 吴满路[1,2] 范桃园[1,2] 张重远[1,2] 李冉[1,2] 陈利忠[1,2,3] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]国土资源部新构造运动与地质灾害重点实验室,北京100081 [3]中国石油大学(北京)地球科学学院,北京102249

出　　处：《地质学报》2017年第5期969-978,共10页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号12120114002101)资助的成果

摘　　要：2013年4月20日芦山Ms7.0级地震后,为研究龙门山断裂带西南段震后的地应力状态,应用水压致裂法和压磁应力解除法在该区开展了2个钻孔的原地应力测量工作。测量结果显示硗碛测点在128～188m深度范围内最小水平主应力的量值为10.47～18.47 MPa,最大水平主应力的量值为19.60～25.83 MPa,方向为N63°～85°W;天全测点在114～142m深度范围内最小水平主应力的量值为5.20～7.73 MPa,最大水平主应力的量值为8.21～9.31 MPa,方向为N59°W。两个测点水平主应力与垂直应力的关系均为σ_H>σ_h>σ_v,其中硗碛测点最大、最小水平主应力与垂直应力比值的平均值分别为5.27和3.01,天全测点最大、最小水平主应力与垂直应力比值的平均值分别为2.60和1.76,表明有利于逆断层活动。通过比较该地区芦山地震前后实测地应力状态,发现芦山地震后,龙门山断裂带西南段的北段(即邛崃大邑西-宝兴北-汶川南一带)和南段(即天全-荥经-泸定-康定一带)应力积累量增加。相同深度范围内,北段硗碛测点震后的应力大小要比地震前有明显的提高,这也与硗碛测点地应力监测结果一致。实测应力方向与震前基本一致,都为NW-NWW。基于实测地应力资料,根据库伦破裂准则和Byerlee定律分析,位于北段的硗碛测点震前部分压裂段的最大水平主应力处于使断层滑动临界值的上下限之间,而地震后最大水平主应力则均已超过断层滑动临界值的上限。位于南段的飞仙关测点震前最大水平主应力均未达到断层滑动临界值的下限,而地震后天全测点的最大水平主应力则均处于使断层滑动临界值的上下限之间。采用最大剪应力(σ_1-σ_3)/2与平均应力(σ_1+σ_3)/2的比值μ_m(断层摩擦)参数评估研究区地应力的积累水平和地震危险性。震前硗碛测点μ_m的量值为0.16～0.72,平均为0.50,震后为0.71～0.81,平均为0.77。震前飞仙关测点μ_m的量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 in- site 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 [�

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 

分 类 号：P315.2[天文地球—地震学]