【作者】 陈斌；

【导师】 瞿伟；

【作者基本信息】 长安大学 ， 测绘科学与技术， 2022， 硕士

【摘要】 强震灾害当前在世界范围特别是我国已成为了一种严重威胁人们生存环境与生命财产安全的主要地质灾害之一。然而,强震释放的巨大能量不仅会造成周边区域地壳形变场发生显著变化,甚至会在发生后的几十年里持续影响周边区域应力场环境,成为促发后续地震发生的潜在因素。2008年5月12日,发生在我国四川的汶川Mw 7.9强震是近几十年来中国大陆震级最大的一次强震,强震的发生不仅对当地人民的生命和财产安全造成了严重的危害,而且也对发震断层及周边区域的构造活动带来深远且显著的影响,其同震和震后效应也成为了国际地学界近年来的研究热点。基于此,本文首先基于青藏高原东南缘1999-2007和2011-2017年高精度GNSS水平速度场,建立了研究域多尺度球面小波地壳运动与应变模型,揭示了汶川强震前后研究区域内较长期地壳运动形变、应变积累及发震断裂和邻近断裂两侧块体的差异运动特征。进一步,在确定发震断层滑动分布模型的基础上,采用了两种地壳分层介质模型,分别计算了研究域内龙门山断裂及邻近断裂同震和震后的库仑应力变化,获得了对汶川强震震后效应的深入认知。本文的主要工作与成果如下:(1)GNSS监测资料揭示出汶川强震前后研究域整体地壳运动与变形具有一定的继承性发展特征,地壳运动整体呈现出在向南东运移同时自身作顺时针旋转运动特征,在龙门山、安宁河、则木河与小江断裂处形成明显的速度差异梯度带,且高应变率值也主要位于主干构造断裂及其附近区域。(2)球面小波模型在不同尺度因子下能够揭示出研究区域不同空间范围内的地壳应变场积累特征。针对于青藏高原东南缘而言,当组合尺度因子33-7时,模型可较好地综合展示出研究区域地壳形变大尺度(整体)与局部变形特征;当尺度因子36时,模型可较好展示出汶川强震后龙门山断裂处的面压缩、主压应变与最大剪应变率的高值现象。(3)基于地壳分层介质模型Ⅰ和Ⅱ计算的龙门山断裂带及附近区域的同震和震后库仑应力变化表明龙门山断裂带中北段本身以及断裂带的东北端和西南端是库仑应力变化的增加区域。其中,东北端的库仑应力变化符号为正的量值在震后5年就已大于阈值,且长期保持增加的趋势,说明该断裂处的地震危险性在增加。西南端的库仑应力变化符号为正的量值虽然增加的幅度较小,但在震后第50年时断裂大部分段的增加量值已大于阈值,说明该断裂处的地震危险性也在提高。(4)基于地壳分层介质模型Ⅰ和Ⅱ计算的研究域内主干断裂的同震和震后库仑应力变化表明鲜水河断裂乾宁-康定段的库仑应力变化符号为正的量值在汶川地震的同震时就已接近阈值,在震后第5年时就已超过阈值,且保持增加的态势,表明此断裂处的地震危险性在增加。更多还原

【Abstract】 Strong earthquake disaster has become one of the main geological disasters at present which seriously threaten people’s living environment and life and property safety in the world,especially in China.The huge energy released by strong earthquakes not only causes significant changes in the crustal deformation field in the surrounding area,but even continues to affect the stress field environment in the surrounding area for several decades after the occurrence,which is a potential factor to trigger subsequent earthquakes.On May 12,2008,the Mw 7.9Wenchuan earthquake occurred in Sichuan Province,China,which was the largest earthquake in mainland China in recent decades.The occurrence of the strong earthquake not only caused serious harm to the lives and property safety of local people,but also brought profound and significant impact on the tectonic activities of the seismogenic fault and the surrounding area.In recent years,the co-and post-seismic effects have become a hot topic in the field of geology.A multi-scale spherical wavelet crustal movement and strain model is established based on the high-precision GNSS horizontal velocity field in the southeastern margin of the QinghaiTibet plateau from 1999 to 2007 and from 2011 to 2017.The characteristics of long term crustal deformation,strain accumulation and differential movement of blocks on both sides of seismogenic faults and adjacent faults in the study area before and after Wenchuan earthquake are revealed.Then,based on the established slip distribution model of seismogenic faults,the Coulomb stress change of the Longmenshan fault and its adjacent faults in the study area are calculated respectively by using two crustal stratified media models,and the post-earthquake effects of the Wenchuan earthquake are gained.The main work and achievements of this paper are as follows:1.GNSS monitoring data revealed that the overall crustal movement and deformation in the study area before and after the Wenchuan earthquake had a certain inheritance of development characteristics.The crustal movement as a whole showed a characteristic of clockwise rotation while migrating to the southeast,and formed an obvious gradient zone of velocity difference at the Longmen Shan,Anninghe,Zemuhe and Xiaojiang faults.The high strain rate values are mainly located in the main structural faults and their vicinity.2.The spherical wavelet model can reveal the accumulation characteristics of crustal strain field in different spatial ranges under different scale factors.For the southeastern margin of the Qinghai-Tibet Plateau,when the combined scale factor 33-7,the model can comprehensively display the characteristics of large-scale(global)and local crustal deformation in the studied region.When the scale factor 36,the model can well display the high values of surface compression,principal compressive strain and maximum shear strain rate at the Longmenshan fault after the Wenchuan earthquake.3.The co-and post-seismic Coulomb stress change of the Longmenshan fault zone and its adjacent areas calculated based on the stratified crustal media models Ⅰ and Ⅱ indicate that the middle-north segment of the Longmenshan fault zone itself and the northeast and southwest ends of the fault zone are the increasing regions of Coulomb stress change.Among them,the magnitude of Coulomb stress with positive sign in the northeast end has exceeded the threshold value five years after the earthquake,and keeps increasing trend for a long time,indicating that the earthquake risk of the fault is increasing.Although the magnitude of the Coulomb stress change sign is positive at the southwest end,the magnitude of the increase is small,but in the50 th year after the earthquake,the increase value of most sections of the fault is greater than the threshold,indicating that the seismic risk of the fault is also increasing.4.The co-and post-seismic Coulomb stress changes of the main faults in the research domain calculated based on the crust layered medium model Ⅰ and Ⅱ show that the Coulomb stress change of Qianning to Kangding of the Xianshuihe fault has been close to the threshold in the Wenchuan earthquake,the five years after the quake was more than threshold,and keep increasing trend,show that the seismic risk of the fault is increasing.更多还原