The Structure Of Shear-Wave Velocity Of Lithosphere Beneath Eastern Yunnan And Adjacent Area By Joint Inversion Of Receiver Function And Surface Wave Dispersion

The continuous collision and compression of the Indian plate and the Eurasian plate not only caused the uplift of the Qinghai-Tibet Plateau,but also led to the growth and expansion of the southeastern edge of the Qinghai-Tibet Plateau.The Xiaojiang fault zone is one of the main boundary fault zones on the southeastern margin of the Qinghai-Tibet Plateau,and it is also one of the most active structures in Sichuan and Yunnan.The existing research results generally believe that there is a low-velocity weak layer in the lower crust.However,whether its distribution range and its origin are related to the material flow in the plateau is still controversial..In addition,the eastern Yunnan area located to the east of the Xiaojiang fault zone was considered a stable platform in the past.In recent years,moderate and strong earthquakes have occurred frequently.Therefore,it is very necessary to reveal the material migration process in the deep crust and mantle of this area,and to explore the dynamic background and seismogenic mechanism of the earthquake origin in this area.Based on the teleseismic observation data recorded by 100 mobile stations in the study area from 2011 to 2013 and 46 fixed stations from 2011 to 2017,this paper uses time-domain iterative deconvolution technology to extract low frequency(Gaussian parameter of 1.0)and High frequency(Gaussian parameter of 2.5)P wave receiving function.After selection,a total of 4153 low-frequency and high-frequency receiver functions were obtained.We establish a simple initial model based on certain prior information.On the basis of linear inversion,we use low-frequency and high-frequency receiver functions to separately and simultaneously combine the two-step inverse of Rayleigh wave phase velocity dispersion and Love wave group velocity dispersion.Based on the simulation technology,the S-wave velocity structure with a resolution of 0.5°×0.5° in the study area was obtained.In the inversion process,in order to make the results more accurate,Bootstrap re-sampling technology is used to analyze and count multiple velocity structures obtained from the same station inversion.The results of the study are as follows:The low-velocity anomaly area of the Xiaojiang fault zone is confined in a limited space in the middle and lower crust,and is not connected with other low-velocity zone around it.We believe that the low-velocity layer is probably not formed by the eastward extrusion of the Qinghai-Tibet Plateau material,but is related to its own deep thermal action.The southern margin of the Sichuan Basin is covered with a thicker sedimentary layer.The results of this article show that the lower crust presents a high velocity overall,which means that it is not significantly affected by the extruded material from the Qinghai-Tibet Plateau and is still a stable geological block.The Cathaysia block located in the southeast of the study area has a thin crust of only 30-40 km.There are high-speed brittle upper crust and low-velocity weak middle and lower crust at the same time under Zhaotong and Lianfeng fault zones.Such deep structural environment may be the inducement of moderate and strong earthquakes in this area.