GPS观测与数值模拟揭示的滇西北地区地壳形变特征及主要断层运动变化  

Crustal deformation characteristics and recent movement changes of main fault zones in northwest Yunnan revealed by GPS and numerical simulation

作　　者：李腊月[1] 刘峡[1] 万永魁 郑智江[1] LI Layue;LIU Xia;WAN Yongkui;ZHENG Zhijiang(First Crust Monitoring and Application Center,CEA,Tianjin 300180,China)

机构地区：[1]中国地震局第一监测中心,天津300180

出　　处：《地质学报》2021年第11期3205-3219,共15页Acta Geologica Sinica

基　　金：国家重点研发计划(编号2018YFC150330506);中国地震局震情跟踪课题(编号2019010203、2020010223)联合资助的成果。

摘　　要：滇西北地区地质构造复杂,强震孕育背景显著。本文利用滇西北地区不同期次(1999~2007期、2013~2018期)GPS观测数据解算地壳应变率场,分析地壳应变率场的动态演化特征。以不同期次GPS观测数据作为边界约束,利用二维有限元接触计算,模拟给出滇西北主要断裂带运动学特征与应力积累速率的变化;并结合汶川、芦山等历史强震和近场跨断层观测等资料,探讨滇西北地区地壳变形特征及其变形机理。结果表明:滇西北地区现今地壳变形特征表现为近东西向的拉张和近南北向的挤压,同时还叠加了南西—北东向的剪切变形,地壳应变率场在不同时段经历了动态调整,但最大主压应变方向在两个时段未发生改变,为NNW向。汶川地震前,滇西北地区主要断裂带的运动速率、运动性质与现有地质、形变结果较为一致;汶川、芦山等地震后,部分断裂带的运动性质与受力状态发生变化,本文分析认为与汶川等远场强震及断裂带近场中强震的发生有关,这些地震对滇西北地区局部应力场产生一定的影响,是部分断层运动性质发生变化的原因之一。The geological structure of the northwest Yunnan is complicated,and the strong earthquake preparation background is remarkable.In this paper,the crustal strain rate fields are calculated using GPS observation data in different periods(1999~2007 and 2013~2018)in northwest Yunnan,and the dynamic evolution characteristics of the strain rate fields are analyzed.Then,the GPS observation data is used as boundary constraints,and based on the block loading method,we simulated the kinematic characteristics and stress accumulation rate of the main fault zones in northwest Yunnan.Finally,combining historical strong earthquakes such as the Wenchuan and the Lushan and near-field cross-fault observation data,we discuss the crustal deformation characteristics and deformation mechanism in the northwest Yunnan.The results showed that the current crustal deformation in the northwest Yunnan is characterized by roughly E—W-directed extension and N—S-directed compression,as well as SW—NE-directed shear deformation.The crustal strain rate fields had experienced dynamics adjustment at different periods,but the direction of the maximum principal compressive strain did not change in two periods,all of which were NNW-directed.Before the Wenchuan earthquake,the movement rate and the nature of the main fault zones in northwest Yunnan were consistent with the existing geological and deformation results.After the Wenchuan earthquake,the movement properties and stress states of some fault zones have changed.In this paper,we suggest that this is related to the occurrence of strong earthquakes in the far field such as the Wenchuan and the moderate strong earthquakes in the near field.These earthquakes have some effects on the local stress fields,which is one of the reasons for the changes of the movement properties of some faults.

关 键 词：GPS观测 GPS应变率场 数值模拟 断层运动 滇西北地区 

分 类 号：P228.4[天文地球—大地测量学与测量工程] P542[天文地球—测绘科学与技术]