芦山地震前后龙门山断裂带西南段地应力状态对比分析

发布时间：2018-10-08 13:28

【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_Hσ_hσ_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的量值为0.31～0.35,平均值为0.32,震后天全测点μ_m的量值为0.53～0.57,平均值为0.55,两个研究区的μ_m的量值均变大。分析认为芦山地震后龙门山断裂带西南段的北段和南段的应力积累量增加,都有发生断层滑动的可能性,尤其是北段。
[Abstract]:After the Lushan Ms7.0 earthquake on April 20, 2013, in order to study the in-situ stress state in the southwest segment of Longmenshan fault zone, the in-situ stress measurement of two boreholes was carried out in this area by using the hydraulic fracturing method and the pressure-magnetic stress relief method. The measured results show that the minimum horizontal principal stress at the Moraine / Residential site is 10.47 ~ 18.47 MPa, in the depth of 128 ~ 188m, and the maximum horizontal principal stress is 19.60 ~ 25.83 MPa, in the direction of N63 掳/ 85 掳W, and the minimum in the depth of 114 ~ 142m in the Tianquan survey site. The magnitude of horizontal principal stress is 5.207.73 MPa,. The maximum horizontal principal stress is 8.21 ~ 9.31 MPa, direction and N59 掳W. The relationship between horizontal principal stress and vertical stress of the two measuring points is 蟽 H 蟽 s h 蟽 v, in which the maximum is observed at the residential moraine, the average value of the minimum ratio of horizontal principal stress and vertical stress is 5.27 and 3.01, respectively, and the maximum is the total measured point. The average values of the minimum ratio of horizontal principal stress to vertical stress are 2.60 and 1.76, respectively, which indicates that they are favorable to the reverse fault activity. By comparing the measured in-situ stress state before and after the Lushan earthquake in this area, it is found that after the Lushan earthquake, The accumulation of stress in the southwest section of the Longmenshan fault zone (i.e. Qionglai, Dayi-Baoxing, North and South Wenchuan) and south (Tianquan, Xingjing, Luding and Kangding areas) has increased. In the same depth range, the post-earthquake stress of the moraine site in the northern section is obviously higher than that before the earthquake, which is consistent with the results of in-situ stress monitoring at the residential moraine site. The measured stress direction is basically the same as that before the earthquake, and all of them are NW-NWW.. Based on the measured in-situ stress data, according to Coulomb's fracture criterion and Byerlee's law, the maximum horizontal principal stress of the fracturing section in the northern section is between the upper and lower limits of the critical value of fault sliding. The maximum horizontal principal stress after the earthquake has exceeded the upper limit of the critical value of fault slip. The maximum horizontal principal stress of the Feixianguan survey point located in the southern segment before the earthquake did not reach the lower limit of the fault slip critical value, while the maximum horizontal principal stress of the Tianquan survey point after the earthquake was between the upper and lower limits of the critical value of fault sliding. The ratio of the maximum shear stress (蟽 1- 蟽 3) / 2 to the average stress (蟽 1 蟽 3 / 2) 渭 M (fault friction) parameter is used to evaluate the accumulation level of in-situ stress and the seismic risk in the study area. Before the earthquake, the value of 渭 m at the moraine measuring point is 0.160.72, the average value is 0.50, and the value after the earthquake is 0.71 ~ 0.81, with an average of 0.77. Before the earthquake, the value of 渭 stack is 0.31 ~ 0.35, the average value is 0.32, the value of 渭 _ m is 0.53 ~ 0.57, the average is 0.55. The value of 渭 _ (M) in the two study areas has become larger. It is considered that after the Lushan earthquake, the accumulation of stress in the southwestern part of the Longmenshan fault zone increases, and that there is a possibility of fault sliding, especially in the northern part.
【作者单位】：中国地质科学院地质力学研究所;国土资源部新构造运动与地质灾害重点实验室;中国石油大学(北京)地球科学学院;
【基金】：中国地质调查局项目(编号12120114002101)资助的成果
【分类号】：P315.2

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