中文摘要：

2013年芦山MS7.0地震发生后，鲜水河断裂北西段的侏倭、虚墟等跨断层测点基线测项均出现不同程度的异常变化，异常核实结果认为基线异常属实.该异常变化是否与芦山地震的发生存在一定关联性，值得深入研究.本文首先分析芦山地震发生前后鲜水河断裂北西段不同基线长度的变化特征.基于鲜水河断裂带及邻区三维非线性黏弹性有限元模型，以GPS观测资料、同震静态滑移量作为约束，通过开展多组数值模拟实验，探讨下地壳不同流变特征下，芦山地震发生前后不同阶段，不同跨断层基线长度的时序动态变化特征.初步研究结果表明，1）侏倭、虚墟基线测点原始观测资料均表现出地震发生时基线长度减小，发生后短时间内反向快速恢复及增加的协同变化；2）在以GPS观测数据为约束的块体间差异性运动的动力学边界条件下，鲜水河断裂表现为左旋走滑运动；3）模拟结果显示，地震发生时测点间距离迅速减小，表现为断层右旋的特征，这与实际观测资料反映的结果一致；4）鲜水河断裂带两侧地块的下地壳黏滞系数分别取10^18Pa·s、10^19 Pa·s时，由于黏弹性松弛效应的影响，造成基线长度在地震发生后短时间尺度内快速增加.对比分析认为，地震后短时间内实测资料反映的基线长度快速增加的特征可能是黏弹性松弛效应与构造作用共同作用的结果.

英文摘要：

The cross-fault baselines at the Zhuwo and Xuxu stations show anomalous characteristics following the 2013 Lushan MS7.0 earthquake, which are confirmed by the preliminary analysis. These provide a unique opportunity for us to explore the possible relation between the anomalous change and the Lushan earthquake. In this paper, we firstly analyze the characters of different baseline lengths along the northwestern Xianshuihe fault before and after the Lushan earthquake. Then, a three-dimensional nonlinear viscoelastic finite element model of the Xianshuihe fault and adjacent regions is constructed. Based on the defined multiple models with different lower crust rheology, we further explore the temporal characters of different cross-fault baselines before and after the Lushan earthquake in terms of the present GPS data and coseismic static slip data, which are applied successively at the model boundary and relative inner nodes, respectively. The results show that the baseline length expresses the coordinated change, which decreases when the Lushan earthquake occurs, and shows the subsequent rapid reverse recovery process in a short time, also a continual increase tendency according to the original observation data at Zhuwo and Xuxu stations. The Xianshuihe fault model successfully reproduces the sinistral strike-slip feature with the block kinematics from GPS-derived velocity constrained. The modeling results suggest the rapid decrease tendency of the baseline length when earthquake occurs, indicating the dextral characteristic of the fault, which coincides with the result from observation data analysis. In a short time following the Lushan earthquake, the modeling result suggests that the baseline length exhibits an increasing tendency due to the viscoelastic relaxation when the lower crust viscosity is assumed to be 10^18Pa·s and 10^19Pa·s, respectively. Comparing the modeling results with the actual observation data, we can conclude that the stress adjustment deduced from the viscoelastic relaxation and tectonic