基于GPS资料研究云南地区地壳形变动态特征*

(云南省地震局,云南 昆明 650224)

最小二乘配置; GPS速度场; 应变参数; GPS速度剖面

Study on Dynamic Characteristics of Crustal Deformation in Yunnan Area using GPS
WANG Yan,HONG Min,SHAO Desheng,WANG Zhimin

(Yunnan Earthquake Agency,Kunming 650224,Yunnan,China)

least squares configuration; GPS velocity field; strain parameter; GPS velocity profile

备注

基于1999—2007年和2011—2013年2期云南地区的GPS速度场资料,结合最小二乘配置方法给出了2个时段应变参数和GPS速度剖面结果,综合分析了汶川8.0级地震前后云南地区地壳变形动态演化特征。GPS 速度场动态演化结果表明:整体上GPS速度场方向从川滇块体南部的南向逐渐转为滇南块体的南东向,块体边界断裂带附近存在明显的相对运动特征。相比于1999—2007年,点位更加密集的2011—2013年GPS速度场结果还反映了断裂带分段变形特征; 在滇南块体及周边地区,南东向的运动有显著的增加。应变参数动态演化结果表明:整体上呈现“中部拉张、两端挤压”的特点; 区域变形(剪切、拉张或挤压)的分布特征与区域主要断裂带的背景运动及变形特征密切相关; 相比于1999—2007年,2011—2013年的拉张变形区有所扩大,并且有向东和向南扩展的趋势; 川滇块体东边界(小江断裂带)整体的挤压变形已经不再显著,主要集中在小江断裂带北段靠北的区域。跨断裂带GPS速度剖面结果显示:小江断裂带左旋滑动速率从北向南逐渐减小(由10 mm/a减至5 mm/a),北段变形宽度较宽; 红河断裂带右旋滑动速率约为4 mm/a,变形宽度较宽; 动态结果表明,汶川地震对2条断裂带变形模式影响较小。

Based on the GPS velocity field data of 1999—2007 and 2011—2013,we used the least squares configuration method and GPS velocity profile results to synthetically analyze the dynamic evolution characteristics of crustal deformation in Yunnan area before and after the Wenchuan earthquake. The dynamic evolution of GPS velocity field shows that the direction is gradually changed from the south of the southern part of the Sichuan-Yunnan block to the south-west of the southern Yunnan block and there is a clear relative motion characteristic near the block boundary fault zone. Compared with the GPS velocity of 1999—2007,the results of 2011—2013 also reflect segmental deformation characteristics of the block boundary fault zone. South-east movement has a significant increase. This may be related to crustal deformation adjustment after the Wenchuan earthquake. The dynamic evolution of strain parameters shows that ‘middle tension,squeeze at both ends' is in the whole area and the distribution of deformation(shear,tension or extrusion)is closely related to the background motion and deformation characteristics of the main fault zone. Compared with results during the period of 1999—2007,the tensile zone in 2011—2013 has been expanded in the eastward and southward direction. The extrusion deformation of the eastern boundary(Xiaojiang fault zone)of the Sichuan-Yunnan block is no longer significant,mainly concentrated in the northern section of the Xiaojiang fault zone,which may be related to the post-seismic deformation adjustment of the Wenchuan earthquake. The GPS velocity profile results show that the left-lateral slip velocity of the Xiaojiang fault zone reduced gradually from north to south(from 10 mm/a to 5 mm/a),and the width of the northern section is wider. The right-hand slip rate of the Honghe fault zone is about 4 mm/a,and the deformation width is wider. The dynamic results show that the Wenchuan earthquake has little effect on the deformation modes of the two fault zones.