汶川地震孕育过程中变形场变化特征研究

揭示与地震孕育过程相关的变形场特征是判别地震孕育阶段及地震危险性的一个重要途径。收集汶川Ms 8.0地震震中区汶川台自2002年10月至汶川地震前的地倾斜观测数据，利用小波分析方法和分段拟合方法，提取了震前地倾斜变化的阶段性特征；利用2001年以来全球卫星导航系统（global navigation satellite system, GNSS）站坐标日解数据，计算了震中附近的泸州GNSS站与周围GNSS站间基线，通过基线变化与区域地震的Benioff蠕变结果的对比，发现了二者的协同性特征。分析结果表明，2004年底汶川台地倾斜速率出现显著下降，西向倾斜速率由230 ms/a减少到130 ms/a；2007年初至发震前减少到60 ms/a；2007年底至发震前未出现指数型加速变化。广州-泸州GNSS基线在2005年初开始的加速缩短异常与Benioff蠕变亏损异常具有较高的相关性，相关系数为0.89；该基线加速缩短持续时间约2.5 a，对应地震的震级估计为7.9级，与汶川地震震级相当，反映了其与汶川地震的应变积累具有一定的相关性。2004年苏门答腊Ms 8.9地震的发生对川滇地区应力应变场影响较为显著，对汶川地震的孕育发生起到了加速作用。研究结果对于认识地壳形变观测的意义及创新地震预测思路具有参考价值。

Pre-Seismic Deformation Related to the Wenchuan Earthquake

  Objectives  Revealing the characteristics of deformation field related to earthquake preparation process is an important way to distinguish earthquake preparation stage and earthquake risk. In order to reveal the significance of crustal deformation observation, the deformation field related to the Wenchuan Ms 8.0 earthquake preparation and the relationship between the deformation field and the seismic activity are discussed from a large spatial scale.  Methods  The original data of crustal tilt observed at Wenchuan station in the epicenter area of the Wenchuan earthquake since 2002 are collected, and the phased characteristics of crustal tilt change are extracted by using wavelet analysis method and piecewise fitting method. Based on the daily solution data of global navigation satellite system (GNSS) station coordinates since 2001, the baselines between Luzhou station and the surrounding stations are calculated. By comparing the baseline change with the Benioff creep, the synergistic characteristics between them are found.  Results  The tilt rate in EW direction at Wenchuan station began to decrease significantly at the end of 2004, from 230 ms/a to 130 ms/a, and it decreased to 60 ms/a until the earthquake occurrence. There was no significant exponential acceleration change from the end of 2007 to the earthquake occurrence. The rapidly shortening anomaly of Guangzhou-Luzhou GNSS baseline in early 2005 has a high correlation with the earthquake creep loss anomaly, and the correlation coefficient is 0.89. The duration of rapidly shortening is about 2.5 years, and the magnitude of the corresponding earthquake is estimated to be 7.9, which is close to the magnitude of the Wenchuan earthquake. The Sumatra Ms 8.9 earthquake in 2004 has a significant impact on the stress-strain field in the eastern Tibet Plateau and accelerates the preparation process of the Wenchuan earthquake.  Conclusions  The different influence of surrounding earthquakes should be considered in the analysis of crustal deformation and earthquake risk. The research results of this paper have reference value for understanding the significance of crustal deformation measurements and innovating earthquake prediction ideas.