基于GNSS资料分析漾濞MS6.4地震前应变时空演变特征

基于云南省内及邻区2009—2020年GNSS观测数据解算结果,在各个测点时间序列和速度场的基础上,采用克里金插值方法估计区域应变率场;以连续基准站时间序列为约束,获取漾濞M_S6.4地震近场区域的块体应变时间序列。分析发现:漾濞地震发生在前期最大剪应变高值区以及面应变高梯度带的张压转换区,发震的时间处于区域应变积累速率逐渐降低的过程之后。震中近场区域均以NW向断层的右旋走滑应变积累为主,且大多呈现持续增强趋势,与漾濞地震的发震断层走向及其破裂特征一致。震前震区东部块体出现了短期应变趋势转折及反向加速的异常现象,反映了应力-应变积累在接近临界破裂状态时的非线性调整。

Analysis of Strain Evolution before the Yangbi MS6.4 Earthquake Based on GNSS Observation Data

Based on the time series and velocity fields of GNSS observation data in Yunnan from 2009 to 2020,the Kriging interpolation method is used to estimate the regional strain rate field. The time series of continuous reference stations are used as constrain,the block strain time series of the near-field area of the Yangbi M_S6.4 earthquake is obtained. The analysis results show that the Yangbi M_S6.4 earthquake happened in the high-value area of the maximum shear strain in the early stage and the tension-compression transition area of the high gradient zone of surface strain. The earthquake happened just after the gradual decrease of the regional strain accumulation rate. From the time sequence of the maximum shear strain and the first shear strain,the local area near the earthquake area is dominated by the accumulation of the right-lateral strike-slip strain of the NW-trending fault,and most of them show a continuous increasing trend. This is in line with the fault trend and fracture characteristics of the Yangbi M_S6.4 earthquake. There was a short-term strain trend turning phenomenon before the earthquake in the eastern area. This reverse acceleration anomaly reflects that the compression strain accumulation rate in the earthquake zone has increased significantly,and the strain accumulation is close to the critical point. The nonlinear adjustment in the rupture state accelerated the gestation process of the Yangbi M_S6.4 earthquake.