利用加密GNSS数据和震源机制解分析川滇块体南部现今地壳活动特性

Study on the Characteristics of Current Crustal Activity in the Southern Sichuan-Yunnan Block Using Dense GNSS Data and Focal Mechanism Solution

利用多源项目获得的补充加密GNSS观测资料计算研究区高空间分辨率的GNSS水平运动速度场和应变率场,采用地震波形资料,通过CAP方法求解震源机制解,在此基础上使用阻尼区域应力反演方法分析川滇地块区域构造应力场的空间分布特征。结合主要断裂的活动特性,综合分析川滇地区的地壳形变特征。结果表明:1)块体浅部的最大主压应力与地表的最大主压应变率由SSE向转变为近SN向,呈现出较好的一致性,GNSS观测至少可反映20 km以内的地壳形变;2)川滇块体南部的东向滑移和顺时针旋转,可能受青藏高原推挤、华南块体阻挡及印度板块与欧亚板块之间北向运动速率自西向东递减而形成的右旋剪切拖拽作用的顺时针力偶的综合影响;3)川滇块体在综合力偶作用下SE向挤出和顺时针旋转的同时,受到走滑逆冲断裂带的吸收转换,使得青藏高原物质SE向挤出有限。

Based on the dense GNSS data from the multi-source projects,we calculate the high spatial resolution GNSS horizontal velocity field and strain rate field of the study area.Using seismic waveform data,the focal mechanism solution is solved by CAP method.On this basis,the damping regional stress inversion method is used to obtain the spatial distribution characteristics of the regional tectonic stress field in Sichuan-Yunnan block.Combined with the seismic activity characteristics of major faults,the crustal deformation characteristics in Sichuan-Yunnan region are comprehensively analyzed.The results show that:1)The maximum principal compressive stress of the shallow part of the block and the maximum principal compressive strain rate of the surface change from SSE to near SN,which present good consistency.The deformation depth inferred from GNSS data can extend to at least 20 km.2)The cause of eastward sliding and clockwise rotation of the Sichuan-Yunnan block are the pushing/thrust effect caused by the Tibet Plateau,the obstruction effect caused by the South China block,and the right-lateral shear dragging effect caused by northward movement decreases from west to east between the Indian plate and the Eurasian plate.3)Under the effects of the clockwise rotation and the absorption and conversion of the strike-slip thrust fault zone caused by the comprehensive couple forces,the SE extrusion of material in the Tibet Plateau is limited.