汶川地震前GPS资料反映的应变率场演化特征

对中国大陆东西向应变率场的研究结果表明，青藏块体西部（92°E以西）东西向拉张区和青藏块体东部（92°E以东）东西向挤压区反映了青藏高原物质东向流动受到了华北 华南地块的阻挡，形成了空间跨度约900 km的压缩区，3期应变率场结果均显示南北地震带中段位于东西向压应变率高值区。川滇地区应变率场结果表明，巴颜喀拉地块东向运动的增强导致了汶川地震震源区面应变率的集中；在东西向挤压高值区逐渐向东迁移的过程中，龙门山断裂带的东西向挤压变形逐渐增强；旋转率场动态演化结果表明，2004—2007年龙门山南段的逆时针旋转变形强度有所减弱，龙门山断裂带中北部的顺时针旋转变形有所增强；主应变率分布特征由散乱到一致的演化特征表明龙门山断裂带闭锁状态伴随着挤压和右旋剪切作用的增强达到了极高点。

EVOLUTION CHARACTERISTICS OF STRAIN RATE FIELD REFLECTED BY GPS DATA BEFORE WENCHAUN EARTHQUAKE

On the analysis of deformation information reflected by GPS velocity data in different reference, the difference between movement and deformation is discussed and we emphasize the deformation is independent from reference basis. On the basis of reliability analysis of GPS strain rate calculation results with least square collocation method, the evolution characteristics of GPS strain rate fields are discussed in different spatial scale. The east west strain rate fields shows that the area in west to 92°E has a EW stretch and the area in the east to 92°E has an EW compression in Qinghai Tibet block. This character reflects the eastward flow of the material of Qinghia Tibet plateau is barred by North China and South China Blocks and forms a spatial span of 900km compression zone, that the strain rate results of 3 sections shows the high compression zone locating at the middle area of South North seismic zone. The strain rate result in Sichuan Yunnan illustrates that the eastward movement of Bayankala block lead to the surface strain concentrating in the source of Wenchuan eartqhake, and the east west compression deformation becomes more intensive in Longmenshan faults while the high area of east west compression transferring to east. The evolution result of rotation rate fields shows that the anticlockwise deformation is weaken in the south of Longmenshan fault and the clockwise deformation has been strengthened in the north of Longmenshan fault from 2004 to 2007. The distribution of principal strain rate changing from disheveled to consistent reveals that the locking status of Longmenshan fault has reached high point with the compression and dextrorotation deformation strengthening.