Analysis Of Current Crustal Movement Characteristics In Sichuan-Yunnan Region By Clustered GPS Velocity Field

Active block is the basic unit of regional tectonic activities,the objectively division of which is of great significance to crustal movement and kinematic research.In this paper,simulation experiments are performed to verify the feasibility of cluster analysis for block partitioning.In the experiment,the effects of GPS station distribution and GPS speed accuracy on clustering results for block partitioning are simulated.Based on the experimental results.The GPS site within the area was screened with a threshold of 2.0 mm/a in one direction.In this study,the hierarchical clustering method is adopted to classify GPS horizontal velocity field of the Sichuan-Yunnan region firstly,and then the F statistic test is employed to correct the misclassification of the GPS site in the geographical space.On this basis,taking account of the DB index and the irreversibility of the hierarchical clustering,the former classification is re-clustered.Finally,the Sichuan-Yunnan region is ultimately divided into six blocks:Tibet block(BYw),Aba block(BYe),Sichuan-Yunnan rhombic block(CD),South China Block(SC),Tengchong-Baoshan Block(DSw)and Indosinian block(DSe).Among them,the west and north boundaries of the CD block are the three-river fault area of "three-river parallel flow" and a velocity step line in the Batang region,respectively.Moreover,main Bayan Har fault divides the Bayan Har block(BY)into two blocks:BYw and BYe.The block division model of the Sichuan-Yunnan region is a reasonable scheme in mathematical sense,which is basically consistent with the results from geological data,can provide an explanation in another dimension for the division of the Sichuan-Yunnan region.Based on the linear block model,the above six blocks were modeled and inverted to obtain Euler vector parameters for each block.Simultaneously,the slip rate of the major faults in the region was calculated:the slip rates of Xianshuihe,Anninghe,the Zemuhe,Xiaojiang,Ganzi-Yushu,Longrioba,Honghe,Lancangjiang,Nujiang and Bayan Hara were 12.4±0.5 mm/a,12.2±0.4 mm/a,11.2±0.5 mm/a,9.0 ±0.4 mm/a,12.8±1.1 mm/a,7.2 ± 0.7 mm/a,3.6 ±0.8 mm/a,5.4±0.9 mm/a,6.3±1.2 mm/a,and 13.7±1.4 mm/a,respectively.The slip rate of the southern part of the fault is somewhat lower than that of the northern part,indicating that the fault has a certain segmentation,and the internal strain of each block is estimated and the strain accumulation in the Sichuan-Yunnan area is mainly distributed in the CD block,which is near the boundary fault,the strike-slip of the fault does not release all the strain.