芦山地震震前应力应变动态过程及同震位错反演研究

发布时间：2018-06-22 08:05

本文选题：汶川地震 + 芦山地震　；参考：《中国地震局地震预测研究所》2015年硕士论文

【摘要】：2013年4月20日,位于龙门山断裂带南段,雅安市芦山县发生Ms 7.0地震。由于震级较大,地震发生区域地质条件复杂,并且与龙门山断裂带中北段发生的汶川地震在时间和空间上相近,因二者之间可能的关联性,分析芦山地震震前地壳形变状态并与汶川地震震后应力变化进行对比就显得十分必要。另一方面,芦山地震发震断层未破裂到地表,不同研究者给出破裂方式的不同,更需要进一步分析芦山地震的同震滑动分布并深究其内在原因。本文以芦山地震为研究对象,以不同时段的GPS速度场数据和芦山地震同震位移数据为约束,对芦山地震震前的应力应变变化及同震位错进行相关研究,主要内容如下:1.基于1999~2007时段和2009~2013时段GPS速度场数据,讨论了芦山地震震前龙门山断裂带附近区域的应变变化及其与应力的关系通过最小二乘配置方法,计算龙门山断裂带附近面应变率及主应变。结果显示,汶川地震前龙门山断裂带中北段应变积累率接近于0,表明这一地区应变积累达到极限,当巴颜喀拉块体继续推挤时,中北段相对南段更容易发生破裂;汶川地震后南段仍处于断层闭锁状态,并且应变积累率增加,使得该地区地震危险性增强;汶川地震前主应变主要集中在鲜水河断裂带,且对其产生左旋变形背景;利用半无限空间位错程序计算汶川地震震后余滑与粘滑造成的主应力变化,与GPS所计算主应变进行对比。结果显示,汶川地震后巴颜喀拉块体南侧主应变的减小与北侧主应变的增大主要受汶川地震震后效应的影响;芦山震源区主应变的变化主要受区域构造的影响;川滇地块受汶川地震震后影响不显著。2、以芦山地震同震位移数据为约束,反演芦山地震同震滑动分布,并分析芦山地震左旋破裂方式产生的原因。在前人研究的基础上,对断层模型采用接近实际的曲面断层设定,断层倾角随深度均匀变化,并用指数函数模拟断层的几何特征。考虑发震断层未破裂到地表特点及地球的分层情况,以芦山地震同震位移为约束,采用SBIF反演方法反演得到芦山地震同震滑动分布。利用最小二乘配置方法分析汶川地震前后芦山地震震源区域主压应变方向角的变化,以加深对芦山地震左旋破裂方式产生原因的理解。结果显示,芦山地震破裂以逆冲为主兼有左旋走滑特征;左旋特征在断层南部更为明显,滑动角随断层深度的增加而减小;将同震位移的模型值与GPS观测值进行对比,两者拟合效果较好,改正了平面断层设定下LS06点位垂向误差较大的情况;汶川地震后,由于龙门山断裂带中北段断层解锁,背景场发生变化,使得芦山地震震源区域主压应变方向角发生顺时针旋转,表明龙门山断裂带南段长期积累的背景场对芦山地震发震断层施加了左旋走滑作用。
[Abstract]:On April 20, 2013, Ms 7.0 earthquake occurred in Lushan County, Ya'an City. Because of its large magnitude and complex regional geological conditions, it is similar to the Wenchuan earthquake in time and space in the middle and north segment of the Longmenshan fault zone, because of the possible correlation between the two. It is necessary to analyze the crustal deformation state before the Lushan earthquake and compare it with the post-Wenchuan earthquake stress change. On the other hand, the Lushan seismogenic fault did not break to the surface of the earth. Different researchers have given different rupture modes, so it is necessary to further analyze the coearthquake slip distribution of the Lushan earthquake and study its internal reasons. Taking the Lushan earthquake as the research object and taking the GPS velocity field data and the coseismic displacement data of the Lushan earthquake at different periods as constraints, this paper studies the stress-strain changes and coseismic dislocations before the Lushan earthquake. The main contents are as follows: 1. Based on the GPS velocity field data from 1999 to 2007 and 2009 to 2013, the strain variation and the relationship between strain and stress in the Longmenshan fault zone before the Lushan earthquake are discussed by the least square collocation method. The surface strain rate and principal strain around the Longmenshan fault zone are calculated. The results show that the strain accumulation rate of the central and northern segment of the Longmenshan fault zone is close to zero before the Wenchuan earthquake, which indicates that the strain accumulation in this area has reached the limit, and when the Bayan Kara block continues to push, the central and northern segment is more prone to rupture than the south segment. After the Wenchuan earthquake, the south segment is still in the state of fault closure and the strain accumulation rate increases, which makes the seismic risk increase in this area, the main strain before the Wenchuan earthquake is mainly concentrated in the Xianshuihe fault zone, and the left-handed deformation background is produced. The variation of principal stress caused by afterslip and stick-slip after Wenchuan earthquake is calculated by using semi-infinite space dislocation program, which is compared with the principal strain calculated by GPS. The results show that the decrease of the main strain in the south side of Bayan Kara block and the increase of the main strain in the north side after the Wenchuan earthquake are mainly affected by the post-earthquake effect of Wenchuan earthquake, and the variation of the main strain in the focal area of Lushan earthquake is mainly affected by the regional tectonics. The Sichuan-Yunnan block is not significantly affected by Wenchuan earthquake. Taking the Lushan earthquake coseismic displacement data as the constraint, the distribution of the Lushan earthquake co-seismic slip is inversed, and the causes of the Lushan earthquake left-lateral rupture mode are analyzed. On the basis of previous research, the fault model is set up with curved surface fault, the dip angle of fault varies uniformly with depth, and the geometric characteristics of fault are simulated by exponential function. Considering the characteristics of unruptured fault to the surface of the earth and the stratification of the earth, the coseismic slip distribution of the Lushan earthquake is obtained by using SBIF inversion method, which is constrained by the Lushan earthquake coseismic displacement. The change of principal compressive strain direction angle of Lushan earthquake focal area before and after Wenchuan earthquake was analyzed by using least square collocation method in order to understand the cause of Lushan earthquake left-lateral rupture mode. The results show that the Lushan earthquake rupture mainly consists of thrust and left-lateral strike-slip, the left-lateral feature is more obvious in the southern part of the fault, and the slip angle decreases with the increase of fault depth, and the model values of co-seismic displacement are compared with the observed values of GPS. After Wenchuan earthquake, the background field changed due to the fault unlocking in the middle and north segment of Longmenshan fault zone, the vertical error of LS06 point was larger than that of LS06 point under the setting of plane fault, after the Wenchuan earthquake, the background field changed because of the fault unlocking in the middle and north segment of Longmenshan fault zone. The rotation of the principal compressive strain direction angle in the focal area of the Lushan earthquake occurs clockwise, which indicates that the long-accumulated background field in the southern segment of the Longmenshan fault zone exerts a left-lateral strike-slip effect on the Lushan earthquake generating fault.
【学位授予单位】：中国地震局地震预测研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.727

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