基于InSAR观测同震地表形变场反演汶川地震断层滑移

发布时间：2018-07-10 10:29

本文选题：汶川地震 + 雷达干涉测量　；参考：《西南交通大学》2015年博士论文

【摘要】：2008年5月12日,以中国四川省汶川县映秀镇为震中(N31.01°,E103.42°)发生了Mw7.9级地震,地震造成龙门山断裂带的映秀-北川断层北东向单侧破裂320km,前山彭县-灌县破裂70km,断层错动引发剧烈的地表运动,造成大量的人员伤亡和经济损失。基于大地测量的空间观测技术,可精确获得大范围同震地表形变场,采用地表形变场反演发震断层的运动模式,可为地震发生机制、区域断层应力迁移、破裂风险评估提供重要的科学依据。星载合成孔径雷达干涉测量(Interferometric Synthetic Aperture Radar,InSAR)是一种新兴的空间大地测量技术,具有监测精度高、覆盖范围广、监测密度大等显著的技术优势。本文采用ALOS卫星覆盖汶川地震前后的PALSAR影像开展雷达干涉测量,获得了汶川地震大范围同震地表形变场。针对InSAR同震形变场存在显著的轨道残余相位误差,开展了基于GPS数据的轨道误差校正,较好地移除了InSAR残余轨道相位。依据相邻条带形变观测一致性原则,利用高质量邻轨数据对干涉条带平滑性予以校正。结果表明,校正后同震形变场的准确度与平滑性得以显著提高,InSAR高相干点残差约3.6cm,精度提高约60%,校正后形变场的邻接平滑因子标准差减小33%。为准确获得汶川地震发震断层的铲状几何模型,提出一种基于倾角渐变分层模型的断层几何确定方法。沿地壳深度方向对断层进行分层离散化,依据断层倾角渐变关系传递倾角搜优区间,以InSAR和GPS地表同震形变为约束进行断层倾角优化。对汶川地震的发震断层几何计算表明,映秀-北川断层沿深度方向具有复杂的几何结构,断层倾角在地表浅层极为陡峭,深度小于2km范围内倾角达73°,在深度2-6km范围内,断层倾角逐渐减小但均大于65°,而在6-14km范围内断层倾角减小趋势增大,14km处倾角降为450,14-20km深度处,断层倾角急剧减小,由45°锐减至2°,呈现为铲状几何结构,在20km深处与彭灌断层一同归并入地壳。为获得汶川地震断层滑动分布模型,将GPS数据和InSAR形变场联合约束用于断层滑动反演,探索出反演模型残差、地震矩与滑动模型粗糙度关系曲线的平滑因子选择方法,在满足模型残差和地震矩联合最小的情况下获得最优平滑因子。联合反演的InSAR数据模型残差约为7.1cm,精度改善超过50%。反演结果表明,断层滑动在震源处以逆冲分量为主兼具少量右旋走滑,沿东北向破裂传播,走滑分量逐渐增大,在断层破裂末端的青川区域,滑动基本以右旋走滑分量为主,在都江堰、高川、北川、房石和红光呈现出五个显著的滑动密集区,最大滑动量达10.03m。为克服单一大地测量数据对断层深部滑动反演不敏感的问题,采用联合断层表面应力变化和GPS形变数据,对汶川地震断层滑动分布进行联合约束反演。与单一大地测量数据的反演结果对比,联合反演方法在深度方向上具有更好的识别分辨能力。计算结果表明,在都江堰区域除了地壳浅部存在显著逆冲滑动成分外,在10-16km的地壳深部接近震源位置处存在一个显著滑动密集区,最大滑动量达9.67m,平均滑动量级超过8.5m。此外,在震源向西南延伸16km处地下7-19km范围内也发现了右旋走滑区域,平均滑动量级超过4.8m。联合反演结果较好地兼容了GPS形变和应力改变两种数据,GPS残差为1.7cm,断层应力改变残差为0.02Mpa,基于滑动模型计算得到汶川地震矩震级Mw=7.96。
[Abstract]:In May 12, 2008, a Mw7.9 magnitude earthquake occurred in the epicentre (N31.01, E103.42) of Yingxiu Town, Wenchuan County, Sichuan Province, China. The earthquake caused the Yingxiu Beichuan fault in the Longmen mountain fault zone to unilaterally rupture 320km, and the Qianshan Peng county irrigation County broke 70km, and the fault caused the severe surface movement, resulting in a large number of casualties and economic losses. The space observation technology based on geodetic measurement can accurately obtain the surface deformation field of large scale and same earthquake, and use the ground form variable field to inverse the motion mode of the seismogenic fault. It can provide an important scientific basis for the seismic occurrence mechanism, the regional fault stress migration, the fracture risk assessment, and the spaceborne synthetic aperture radar interferometry measurement (Interferometric Synthetic). Aperture Radar, InSAR) is a new spatial geodetic technique with high monitoring precision, wide coverage and large monitoring density. This paper uses ALOS satellite to cover the radar interferometry before and after the Wenchuan earthquake, and obtains the surface deformation field of the large scale of Wenchuan earthquake. In view of InSAR same earthquake There is a significant orbital residual phase error in the deformation field, the orbit error correction based on GPS data is carried out, and the phase of the residual orbit of the InSAR is well removed. According to the consistency principle of the observation of the adjacent strip deformation, the smoothness of the interference strip is corrected by the high quality adjacent rail data. The result shows that the accuracy of the correction of the same earthquake deformation field after correction is obtained. The smoothness can be improved remarkably, the InSAR high phase dry point residual is about 3.6cm, the accuracy is improved by about 60%, the standard deviation of the adjacent smooth factor of the corrected field is reduced 33%. to obtain the shovel geometry model of the Wenchuan earthquake fault accurately, and a method of fault geometry determination based on the gradient stratification model is proposed. Stratified discretization is carried out, and the dip search interval is transmitted according to the gradient relation of the fault dip, and the fault dip is optimized by the same seismic deformation as the InSAR and GPS surface. The geometric calculation of the seismogenic fault of the Wenchuan earthquake shows that the Yingxiu Beichuan fault has a complex geometric structure along the depth direction, and the dip angle of the fault is steep and deep in the shallow layer of the surface. In the range of less than 2km, the dip angle is 73 degrees. In the range of depth 2-6km, the dip angle of fault gradually decreases but is more than 65 degrees, and the trend of the dip angle decreases in the 6-14km range, the dip angle of 14km is reduced to 450,14-20km depth, the dip angle of the fault decreases sharply from 45 degree to 2 degree, and it is now a shovel geometry structure, together with the Peng irrigation fault in the depth of 20km. In order to obtain the Wenchuan seismic fault slip distribution model, the GPS data and the InSAR deformation field are combined to be applied to the fault slip inversion, and the smoothing factor selection method of the inversion model residual and the relation curve of the seismic moment and the sliding model roughness is explored, and the optimal method is obtained to meet the minimum of the model residual and the seismic moment. The residual error of the InSAR data model of the combined inversion is about 7.1cm, and the precision improvement over 50%. inversion shows that the fault slip is mainly the thrust component with a small amount of dextral strike slip in the source of the epicenter, propagating along the northeast to rupture, the strike slip component gradually increases, and the slip is basically the dextral strike slip component at the Qingchuan region at the end of the fault rupture. In Dujiangyan, Dujiangyan, Gao Chuan, Beichuan, housing stone and red light, there are five significant sliding areas. The maximum slip amount is up to 10.03m. to overcome the insensitivity of the single geodetic data to the deep slip inversion of the fault. The joint fault surface stress change and the number of GPS deformation are used to jointly restrain the sliding distribution of the Wenchuan seismic fault. Compared with the inversion results from the single geodetic data, the joint inversion method has a better recognition resolution in the depth direction. The results show that there is a significant sliding area in the deep crust of the 10-16km in the area of the crust of the Dujiangyan, except for the significant thrust slip in the shallow part of the crust. The slip volume is 9.67m and the average sliding magnitude exceeds 8.5m.. The right spin strike slip area is also found in the 7-19km range of the south-west extension 16km. The average slip magnitude exceeds the 4.8m. combined inversion results, which is well compatible with the GPS deformation and stress change two kinds of data, GPS residual difference is 1.7cm, the fault stress change residuals are 0.02Mpa. The Wenchuan earthquake moment magnitude Mw=7.96. is calculated by sliding model.
【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P315.7;P228.4

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