汶川地震后青藏高原东北缘GPS地壳形变场特征研究

发布时间：2018-06-22 13:03

本文选题：GPS + 汶川地震　；参考：《中国地震局地震预测研究所》2013年硕士论文

【摘要】：空间大地测量GPS技术广泛应用于地壳形变监测以来，其在孕震形变场识别，同震位移场观测和震后地壳运动变化监测等方面都发挥着重要作用，已成为现今研究与地震相关的地壳形变场的主要手段之一。2008年5月12日，四川省汶川县发生了Ms8.0级地震，因其震级较大，必然对周边地壳形变场产生一定影响，因此，利用GPS数据对震后形变场特征问题进行研究显得十分必要。本文以青藏高原东北缘作为研究区域，基于不同时段GPS数据，对汶川地震后该区地壳形变场特征进行分析，，论文主要完成了工作如下： 1.基于1999～2007时段和2007～2009时段GPS数据，讨论了震后短期青藏高原东北缘地壳运动变形特征及其成因问题。通过对庄浪河断裂和祁连山中东段断裂进行跨断层剖面分析，表明地震前后这两条断裂滑动速率变化显著；采用球体位错模型获得汶川地震同震位移场分布，结果显示同震对这两条断裂有一定影响，但更大程度上不是来自同震，而是由震后形成的；计算震后一年粘弹性松弛效应在青藏东北缘产生的变形，结果显示变形很小，可以忽略；反演了龙门山断层面上震后余滑的滑动分布，再计算该滑动分布在青藏高原东北缘产生的地壳变形，结果表明震后余滑对该区域影响微乎其微，可以忽略；通过分析地震前后块体欧拉矢量变化，显示受同震分布样式影响，不同块体震后运动调整的差异对震后变形的形成有重要影响；分析认为汶川地震震后短期地壳变形特征的形成不是由现有的震后余滑、粘弹性松弛等变形机制模型所能解释的，可能是由于青藏高原东北缘属于多块体构造系统，震后块体间的运动调整差异使得块体边界带的运动发生显著变化。 2.基于1999～2007、2007～2009和2009～2011时段GPS数据，研究了震后青藏高原东北缘地表形变场特征。利用最小二乘配置方法获得青藏高原东北缘地表应变率场（包括最大剪应变率场和面应变率场），分析了区域地表应变率场特征，结果显示2007～2009时段部分区域地表应变率变化显著，2009～2011时段则有所恢复；通过块体欧拉矢量法计算了主要断裂的滑动速率，利用跨断层剖面分析距断裂不同尺度处变形特征，结果表明在2007～2009时段，托莱山断裂、冷龙岭断裂和金强河断裂左旋走滑速率明显增大，断裂变形在断裂附近50km范围内尤为显著，在2009～2011时段，各断裂滑动速率和跨断层剖面结果均与震前1999～2007时段相差不大。 3.主要断裂带深部闭锁程度与滑动亏损分布及其震后变化为利用GPS地表观测资料研究青藏高原东北缘地区主要断裂带应变积累状态及其在汶川地震后的变化，开展了基于负位错模型反演主要断裂深部闭锁程度和滑动亏损分布，分析主要断裂深部应变积累特征，以1999～2007年GPS速度场数据为约束反演了汶川地震前主要断裂带上断层闭锁程度和滑动亏损分布，进一步用2007～2009年、2009～2011年资料反演了汶川地震后主要断裂带断层闭锁和滑动亏损的变化。结果显示震前金强河断裂、毛毛山断裂和六盘山断裂南段震前闭锁程度强，并且在2007～2009时段进一步增强，2009～2011时段，托莱山断裂和冷龙岭断裂闭锁程度有一定增强，金强河断裂变化不大，闭锁依然较强，其他断裂均闭锁有所减弱，可能受到了日本9.0地震对该区域影响。综合形变场特征认为金强河断裂未来强震危险性相对较高。
[Abstract]:SPATIAL GEODETIC GPS technology has been widely applied to the monitoring of crustal deformation. It has played an important role in the identification of seismogenic deformation field, the observation of the same earthquake displacement field and the monitoring of the change of the crustal movement after the earthquake. It has become one of the main sections of the crustal deformation field related to the earthquake in May 12th, Wenchuan County, Sichuan province. It is necessary to have a certain influence on the deformation field of the surrounding crust because of the large magnitude of the Ms8.0 magnitude earthquake. Therefore, it is necessary to study the characteristics of the deformation field after the earthquake by using the GPS data. This paper takes the northeastern margin of the Qinghai Tibet Plateau as the study area and based on the GPS number of different periods of time, the crustal deformation field of the Wenchuan region after the earthquake is introduced. In line with the analysis, the main work of the paper is as follows:
1. based on the GPS data of 1999~2007 and 2007~2009 periods, the crustal movement and deformation characteristics of the northeast margin of the Qinghai Tibet Plateau and their causes are discussed shortly after the earthquake.
Through the cross fault section analysis of the Zhuanglang River fault and the east part of the Middle East section of the Qilian mountain, it is shown that the slip rates of the two faults are significant changes before and after the earthquake, and the distribution of the seismic displacement field of the Wenchuan earthquake is obtained by using the model of the sphere dislocation. The results show that the same earthquake has a certain effect on the two faults, but to a great extent, it is not from the same earthquake, but not the same shock. After the earthquake, the deformation of the viscoelastic relaxation effect of one year after the earthquake was calculated in the northeastern margin of the Qinghai Tibet Plateau. The results show that the deformation is very small and can be ignored. The slip distribution of the post earthquake on the Longmen Mountain Fault layer is retrieved and the crust deformation caused by the sliding distribution on the northeastern margin of the Qinghai Tibet Plateau is calculated. The results show that the residual slip after the earthquake is on the region. The influence of the Euler vector changes on the block body before and after the earthquake shows that the difference of the post earthquake movement adjustment of different blocks has an important influence on the formation of the post earthquake deformation, and it is considered that the formation of the short-term crustal deformation characteristics after the Wenchuan earthquake is not by the existing post earthquake residual slip and the viscoelasticity. The deformation mechanism model of sexual relaxation may explain that the northeast margin of the Qinghai Tibet Plateau belongs to the multi block structural system, and the movement adjustment difference between the post earthquake blocks makes the movement of the block boundary zone significantly change.
2. based on the GPS data from 1999~20072007 to 2009 and 2009~2011 periods, the characteristics of the surface deformation field in the northeastern margin of the Qinghai Tibet Plateau were studied.
The ground strain rate field (including the maximum shear strain rate field and the surface strain rate field) on the northeastern margin of the Qinghai Tibet Plateau is obtained by using the least square method, and the regional surface strain rate field is analyzed. The results show that the change of the surface strain rate in the part of the 2007~2009 period is significant and the 2009~2011 period is restored; the block Euler vector method is used. The slip rate of the main fracture is calculated, and the deformation characteristics at different scales are analyzed by cross fault section. The results show that in the 2007~2009 period, the Laishan fault, the Leng Long Ling fault and the Jin Qiang River fault are obviously increased, and the fracture deformation is particularly prominent in the 50km fan enclosure near the fault, and in the 2009~2011 period, the fracture slip is slippery. The results of dynamic velocity and cross fault section are not significantly different from those of the 1999~2007 period before the earthquake.
3. the deep block degree and slip loss distribution of major fault zones and their post earthquake changes.
In order to study the strain accumulation state of the main fault zone in the northeastern margin of the Qinghai Tibet Plateau and the changes in the Wenchuan earthquake, a negative dislocation model is used to inverse the depth of the main fault and the slip loss distribution based on the negative dislocation model. The strain accumulation of the main faults is analyzed, and the data of the 1999~2007 year GPS velocity field is taken as the data of 1999~2007 years. The degree of fault atresia and slip loss distribution on the main fault zone before Wenchuan earthquake are retrieved, and the changes of fault locking and slip loss in the main fault zone after Wenchuan earthquake are retrieved from the data of 2007~2009 years and 2009~2011 years. The results show that the Jin Qiang River fault, Maomao Shan fault and the southern segment of six Panshan fault before the earthquake were locked. The degree of the Laishan fault and the cold Long Ling fault is enhanced in the 2009~2011 period, and the faults of the Laishan fault and the Leng Long Ling fault have a certain enhancement. The fault of the Jin Qiang river is not changed, the interlocking is still strong, and the other fractures are locked down, which may be affected by the 9 earthquake in Japan. The risk of future strong earthquakes is relatively high.
【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】：2013
【分类号】：P228.4;P542

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