Research On Crustal Deformation And Dynamic Background Of Eastern Region Of The Red River Fault

The eastern region of the red river fault which located at the southeastern margin of Tibetan Plateau is the frontier of the collision between the India and Eurasia.As an important channel of east flowing-material of Tibet,there were frequent strong earthquakes happened in this study area which lies several large fault zones.Study area become the "natural laboratory" of crustal deformation and tectonic evolution law due to the advantaged geological tectonic environment.Large scale deformation of underground medium produces a seismic wavelength scale earthquake anisotropy,which makes an effective means to investigate the deformation and the movement process of underground medium.Thus,investigating the upper and lower crust anisotropy of eastern region of the red river fault and combining previous research which focus on the upper mantle anisotropy,S wave velocity structure and the GPS strain field make a comprehensive analysis of the crustal deformation characteristics and the flow patterns of the lower crustal flow in the southeastern margin of Tibet affected by the "east-running” material of Tibet is meaningful to understand the collision between the India and Eurasia,crustal deformation,regional tectonic relationship and dynamic background of the southeastern margin of Tibetan Plateau.To obtain the higher density distribution of crust anisotropy beneath eastern region of the red river fault,we extracted the p-wave receiving function with Gaussian parameter of 2.5 based on 255 events greater than 6.0Ms recoded by 158 broadband mobile stations from the Chin Arry Phase I and 180 events greater than 6.2Ms recoded by 39 fixed stations from the China national seismic network layout in the area.And then investigating the Pms and Pis split beneath stations by azimuthal stacking,arrival time variance minimizing and layer stripping.It shows that the splitting time of Pms phase varies from 0.08 s to 1.22 s,with an average of 0.54 s from the result.The fast polarization directions of Pms in southern margin of Sichuan basin is approximately NE-SW,and generally NNW or N-S in the north of Sichuan-Yunnan rhomboid block,and a chaos in most central Yunnan with a counterclockwise rotation between 25°N and 27°N,and a counterclockwise rotation from NW to NE.The results of two layers of anisotropy showed that the lower crust splitting time was generally greater than that of the upper crust,so it can be verified that the crustal anisotropy is mainly generated with the lower crust.And it is only coupled that the upper and lower crust in the north of Sichuan-Yunnan rhomboid block,while the other areas are decoupled.Besides this,it can be considered that there is only coupling between the lower crust and the mantle in Sichuan-Yunnan rhombic body.The results show that the anisotropy of Sichuan-Yunnan rhombic block reflects the present crustal deformation,while the anisotropy results of the southern margin of Sichuan basin and south China block reflect the early crustal deformation.Besides,the fast polarization directions of the stations which close to faults are parallel to the faults,implying the orientation of anisotropic substances in crust is constrained by faults.The upper-crustal deformation in the study area is mainly affected by the regional stress field and fault.The lower crustal deformation is mainly controlled by the combined action of the lower crustal flow and fault?It can be speculate that after entering the sichuan-yunnan rhombic block,the "escaping" material from the south of the Tibetan Plateau is impededThe eastward flow of the lower crust thickens the crust of the northern block,which is impeded by the hard Sichuan basin.After passing through the Lijiang-Jinhe fault the lower crust material that continued to flow southward entered the central Yunnan block and was blocked by the Red-River fault and failed to flow smoothly into the Indochina block.Because the lower crust beneath the Xiaojiang fault is an anomaly at a low speed,the lower crust flow accumulates outside the southern subblock in the middle of Yunnan,and a small part of the crust flows into the South China block through the “pipeline”.