汶川大地震前后GPS观测的精密单历元解得到的震区地壳运动

Crustal movement in the earthquake area before and after 2008 Wenchuan earthquake as detected by precise single epoch positioning of GPS observations

利用BERNESE软件的单历元观测值双差定位功能,获取了接近2008年5月12日汶川MS8.0大地震震中5个GPS观测站(PIXI,CHDU,JYAN,NEIJ和LUZH站)震前的短临位移过程及震后短时间的位移.通过拟合和对比分析,讨论了单历元解的精度.计算结果表明,以YANC站为固定站,LUZH站震前5月9日N(南北向)、E(东西向)和U(垂直向)3个分量日变化明显异常;而近震中的PIXI,JYAN和NEIJ站震前1小时内垂直位移非常显著,特别是离震中36km的PIXI站在震前不到1小时的时间内垂直位移变化达300mm以上.震后,PIXI站的水平位移更为突出,2个分量均超过400mm,十分接近高精度的周解结果.这些变化均显著大于单历元解的误差水平.尽管目前的GPS数据处理尚不能实时获取单历元解,但所得到的结果为观测研究大地震近震中临震前的地壳运动提供了依据.

Displacement time series of precise single epoch positioning imminently before the great Wenchuan earthquake on May 12,2008,and shortly after the earthquake at 5 GPS stations of PIXI,CHDU,JYAN,NEIJ and LUZH are obtained from the double difference positioning of the BERNESE software.Through analysis on the best fit result and comparison of different results the accuracy of the single epoch solutions is discussed.The result of data processing with YANC used as a fixed station show that there were significant anomalies in 3 displacement components of NEU at LUZH station on May 9 before the earthquake,while the vertical displacements at stations of PIXI,JYAN and NEIJ,close to or near the epicenter,were quite significant within 1 hour before the earthquake,especially the vertical displacement at PIXI station,36 km to the epicenter,accumulated to more than 300 mm within 1 hour before the earthquake.The post seismic horizontal displacements at PIXI station were even more striking with more than 400 mm displacement for both components,quite close to the result of more precise weekly solutions.All these changes are significantly larger than the RMS（rooted mean squares）of the single epoch positioning solutions.Though the real time single epoch positioning solutions can not be obtained at present,the result may be used as an evidence in the study on crustal movement close to or near the epicenter imminently before great earthquakes.