基于GPS应变与震源机制解应力反演喜马拉雅构造带现今地壳形变特征

喜马拉雅构造带及其临近区域是印度板块与欧亚大陆板块挤压碰撞的前缘地带.本文利用GPS实测速度场与震源机制解数据分别计算了研究区域现今地壳岩石圈表面的GPS应变场及岩石圈内部的主应力分布,研究了印度板块持续挤压作用下板块边界带地壳岩石圈现今地壳形变的空间分布特征.结果显示,南北向的剧烈挤压变形与东西向的拉伸变形是现今青藏高原南缘地壳岩石圈的主要变形特征.其中南北向的地壳挤压变形主要集中在主前缘冲断带与雅鲁藏布江缝合带之间.东西方向上,南北走向的亚东—谷露断裂是区域地壳东西向伸展变形的重要分界断裂.75°E是研究区域地壳形变的另一条显著不连续边界,其西侧地壳主压应变强度低、方向弥散且最大主压应力方向一致性较差,而东侧地壳主压应变方向与主压应力方向以及地壳水平运动速度场方向均具有较好的一致性.布格重力异常的小波多尺度辨析结果显示该分界带与循喜马拉雅西构造结楔入欧亚大陆的印度板块密切相关.

Study on current crustal deformation of the Himalayan tectonic zone by GPS strain-rate estimation and focal mechanism stress inversion

The Himalayan orogenic belt and its adjacent regions are the front zones of the compression and collision between the Indian plate and the Eurasian plate. In this paper, the GPS strain field on the surface of the current crust and lithosphere in the study region and the distribution of the principal stress in the lithosphere are calculated respectively by using the GPS measured velocity field and earthquake mechanism solution data. The spatial distribution features of the current crustal deformation of the crust and lithosphere in the plate boundary belt under the continuous compression of the India plate are studied. As is shown in the results, the main deformation characteristics of the crust and lithosphere in the southern margin of the Qinghai Tibet Plateau are the intensely-compressed deformation in the north-south direction and the extensional deformation in the east-west direction. The north-south crustal deformation is mainly concentrated between the main front thrust belt and the Brahmaputra suture belt. In the east-west direction, the north-south Yadong-Gulu rift is an important boundary rift for the east-west extensional deformation of the regional crust. 75°E is another significant discontinuous boundary of crustal deformation in the study region. The main compressive strain in the west side of the boundary is low in intensity, diffuse in direction and poor in consistency with the direction of the maximum main compressive stress, while the main compressive strain in the east side is consistent with the direction of the main compressive stress and the direction of the horizontal velocity field. The result of wavelet multi-scale analysis of Bouguer gravity anomaly shows that the boundary zone is closely related to the Indian plate wedged into Eurasia along the west structural junction of Himalaya.