利用GPS形变资料研究天山及邻近地区地壳水平位移与应变特征

HORIZONTAL MOVEMENT AND STRAIN CHARACTERISTICS IN TIANSHAN AND ITS ADJACENT REGION WITH GPS DEFORMATION DATA

以天山及邻近地区的230个GPS观测站长期水平运动速率为基础,计算并绘制了该地区GPS站速度场及地壳水平应变场分布图,得到了以下结论:在以欧亚板块为参考基准的背景下,天山及邻近地区GPS速度场表明,天山地壳缩短方式由南向北,以东经77°±1°(北纬38°～42°)为界向两侧逐渐递减;同时表明,板块的推挤作用力随着天山的褶皱变形减小相应趋缓.天山及邻近地区的主压应变方向分布近北北西向,基本与天山山体走向正交.反映了在印度板块碰撞推挤的强烈构造运动影响下天山及邻近地区的最大主应力分布与变化情况.其最大剪应变场集中分布在两个区域:北天山的吉尔吉斯斯坦依赛克湖附近;南天山伽师与帕米尔弧形断裂交会地带.整个地区多年来的地震震中分布,反映了该区域大地震通常发生在剪应变高值区或其边缘地带.

Based on the multiple-term horizontal velocity solutions of 230 GPS monitoring sites in Tianshan and its adjacent region, the GPS site velocity fields and crustal horizontal strain fields in the area have been obtained. The results show that the crustal shortening rate of Tianshan, with the longitude （77°±1°）E as the boundary, gradually decreased towards two sides, from the south to the north, indicating that the pushing force of plate becomes weaker along with the fold deformation decreasing of the Tianshan. The direction of principal compressive strain of Tianshan and its adjacent area, nearly NNW, is basically perpendicular to the Tianshan cordillera trend, suggesting the distribution and variation of maximum principal compressive stress in Tianshan and its adjacent region resulted from collision and extrusion of Indian Plate. This paper indicates that the maximum shear strain field mainly concentrates on two areas, one is Isyk lake of North Tianshan, Kyrgyzstan, and the other is the juncture of Jiashi （South Tianshan） and Pamir arc faults. In the above areas, it can be shown from the epicentral distribution that the strong earthquakes mostly occurs at the high shearing strain accumulation filed or its edge.