摘要
根据1990年青海共和地震震后地表垂直形变,通过模型拟合得到了支配共和地区震后形变场时空演化的形变源及其力学机制.分析穿过断层的震前1期和震后6期水准数据,结果表明震后垂直形变具有以下特征:①震后震区上盘继续发生继承性的大幅度上升,其中震后头一年上升速率最大;②震后上升区范围显著,范围随时间变化不大,但较同震形变上升区范围增大;③震后相邻测站高差观测值的时间序列明显具有对数衰减特征或指数衰减特征,衰减特征时间分别为0.165年和1.344年.本文还发展了一个利用水准数据与连续介质位错模型研究震后形变机制的新方法.该方法用相邻水准点之间的原始高差观测值而非它们相对参照点的积分值来约束连续介质位错模型,可以有效减少误差累积带来的偏差并充分利用观测数据.利用这一方法的初步分析结果表明,断层震后滑移和介质黏弹性松弛共同导致了共和地震震后形变.前者表现为发生在断层面及其延伸部分的滑移,特别是位于主破裂上方沉积层内的滑移;后者则表现为下地壳与上地幔内的黏弹性松弛,黏滞系数为1020Pa.s量级.
We model leveling deformation data observed on the Earth＇s surface following the 1990 MS7.0 Gonghe earthquake,Qinghai province,to infer the postseismic deformation source and mechanism. By analyzing the leveling data observed one epoch before and six epochs after the quake across the coseismic fault,we find the following characteristics of the postseismic deformation：① the near field on the hanging-wall side of the coseismic rupture continued to uplift at large scale after the earthquake,with the highest rate measured in the first year; ② the scope of postseismic uplifting region was larger than that of coseismic uplifting,but did not change during the postseismic deformation period; ③ the time series of elevation change between two adjacent benchmarks can be modeled by a logarithmic relaxation function or an exponential relaxation function,and the relaxation time constants are 0.165 years and 1.344 years,respectively. In the paper we also introduce a new method using leveling data and dislocation model in continuum to investigate the source and mechanism of postseismic deformation. The new method utilizes the raw observations of elevation differences between two adjacent benchmarks,not their integrals with respect to a reference point,to constrain a dislocation model in a continuum,effectively reducing biases introduced from cumulative errors due to data integration and making full use of the leveling data. Our preliminary result suggests that two mechanisms operate simultaneously to produce the postseismic vertical deformation of the surface：（a） afterslip on the coseismic rupture fault plane of the main shock and its peripheral extensions,particularly upward to the sediment layer above the main rupture,and （b） viscoelastic relaxation of the lower crust and upper mantle,with a viscosity in the order of 1020 Pa·s.
出处
《地震学报》
CSCD
北大核心
2010年第5期557-569,共13页
Acta Seismologica Sinica
基金
国家重点基础研究发展规划项目(2004CB418403)
国家自然科学基金重点课题(40334042)
地震科学联合基金(C08048)
地震行业科研专项经费项目(200708002)资助
关键词
共和地震
水准测量
震后形变
震后滑移
黏弹性松弛
Gonghe earthquake
leveling measurements
postseismic deformation
afterslip
viscoelastic relaxation
