区域网GPS观测得到的2008年汶川M(下标 s)8.0地震前的地壳水平运动

The Wenchuan M(subscript s)8.0 earthquake on May 12, 2008, occurred in an area with dense GPS observation stations in the regional network of CMONOC (the Crustal Movement Observation Network of China). The regional network with 1000 GPS stations for non-continuous observations carried observations in 1999, 2001, 2004 and 2007. Horizontal displacements at GPS stations in the regional network before the Wenchuan earthquake show that the main driving tectonic force of the earthquake was the northward pushing of the Indian plate, with additional pushing of plates on the eastern and southern side. In comparison with the displacements in other regions, a most striking feature of the horizontal displacements near and around the earthquake area is the eastward diverging motion, that is, the stations north of the epicenter moved in the ENE direction while those south of epicenter moved in ESE direction, with small displacements at stations near the epicenter. The accuracy of estimated strains is briefly discussed. In order to obtain the anomalous information before the earthquake, both methods of trend surface fit and statistics have been used in the study with the aim of looking for potential epicentral area from the strain accumulation in the regional network observed from 1999 to 2007 before the Wenchuan earthquake. Besides the epicentral area of the 2001 Kunlun Mountain earthquake of M(subscript s)8.1 in 2001, the best fit result of a trend surface of strain accumulation from 1999 to 2007 in the regional network before the earthquake show that the Wenchuan earthquake occurred at the eastern fringe of a large region with remarkable accumulation of the first shear strain, and also at the northeastern fringe of a smaller region with significant areal compression accumulation. Statistics of the accumulation of strain components show that there were also anomalous strain distribution patterns in this region and its neighborhood with increasing accumulation of both shear strain and areal compression.