汶川地震前后四川盆地CORS站运动特性分析

为探讨四川盆地在汶川地震前后地壳运动的规律，本文对2006年3月至2012年9月四川12个连续运行参考站（Continuously Operating Reference Stations, CORS）6年多的观测资料进行了详细的处理和分析。通过比较震前震后CORS站运动的相似性和差异性发现：由于震后形变的影响，震后第一主成分(Principle Component First, PC1)的贡献率下降20%~40%；震后多站的速度场发生了明显的变化，突出表现在PIXI，CHDU，MYAN等站，YAAN，QLAI站处于闭锁状态；盆地垂直分量的周年振幅在震前一年偏大，震后逐年减小。以上发现表明汶川地震可能改变了四川盆地原有的运动特性。

Characteristics of Position Time Series at CORS Stations in Sichuan Basin before and after Wenchuan Earthquake

The sites’ movement characteristics before and after Wenchuan Earthquake are investigated using the daily position time series of 12 continuously operating reference stations (CORS) in Sichuan Province from 2006 March to 2012 September. The displacements due to surface mass loading effects such as pressure loading, nontidal ocean loading, snow depth and soil moisture loading have been calculated and removed to reduce the root mean square (RMS) of the vertical component. A spatial filtering method based on the principle component analysis (PCA) is employed to extract the common mode errors (CME) from the daily time series. The method of maximum likelihood estimation is also utilized to choose the optimal noise model and assess the model parameters of the time series. The results indicate that the spatial response of the first principal component with the PCA analysis is reduced obviously by 20%~40% after the earthquake due to the effect of the post-seismic deformation. The velocity field has also changed obviously, especially at the PIXI, CHDU and MYAN sites, while they seem to be locked at the YAAN and QLAI sites. The annual amplitude of Sichuan Basin is the largest just one year before the earthquake, and after that it becomes smaller gradually. The results above imply that the Wenchuan Earthquake has potentially changed the movement characteristics of Sichuan Basin.