Study On Segmented Activity Characteristics Of Red River Fault Zone Based On GPS Data

Sichuan-Yunnan region is located in the southeast margin of Tibet Plateau,which is the key area to coordinate the Cenozoic intracontinental tectonic deformation in Southeast Asia.Since the late Quaternary,a series of strong active faults have been bred there.The Red-River fault zone is an important block boundary fault in Sichuan-Yunnan region.Understanding the activity characteristics of different sections of the Red-River fault zone is of great significance for us to understand the movement characteristics of Sichuan-Yunnan region and the southeastern margin of the Tibet Plateau.This paper integrates the GPS data of the study area and makes a preliminary analysis.Based on the GPS data published by Wang et al.(2020),the GPS velocity field in Sichuan-Yunnan region from 1999 to 2018 was obtained by using the GPS stations encrypted on the Red River fault zone from 2014 to 2018.The Red River fault zone was subdivided and the surrounding area was divided into blocks.The Red River fault zone can be divided into three segments from north to south,the north segments from Eryuan to Midu,the middle segments from Midu to Yuanjiang,and the south segments from Yuanjiang to Yuanyang.The surrounding area can be divided into five relatively independent blocks: South China block,Daliangshan block,Northwest Sichuan block,Central Yunnan block and Southwest Yunnan block.Through comparative experiments,the best fitting parameters of strain field interpolation are obtained,and the strain field of the study area is inversed,and the activity characteristics of the main faults in the study area are preliminarily obtained:the south segment of Xiaojiang Fault Zone and the north segment of Red River fault zone have strong tectonic activity characteristics;the extension movement trend of Red River fault zone is transformed from the north segment to the compression movement trend of the middle and south segment;The Chuxiong-Jianshui fault zone and Wuliangshan fault zone on the left and right sides of Red River fault zone are more active in the middle and south part of the Red River fault zone.Through comparative experiments,the Lijiang-xiaojinhe fault and Xiaojiang Fault are added to carry out modeling analysis,and the model resolution of the three fault zones is tested respectively.The node models of the three fault zones are: Red River fault zone 4 * 4(strike node number * dip node number),Xiaojiang Fault zone6 * 4 and Lijian-xiaojinhe fault zone 4 * 4.Using the three-dimensional elastic block model,the motion parameters of each block in the study area,the sliding rate and the degree of earthquake locking of the three fault zones are obtained.Finally,combined with the results of two-dimensional dislocation model of surrounding faults,the characteristics of fault zone locking and regional strain field are discussed and analyzed.The following conclusions are drawn:(1)the north segment of Red River fault zone still has high seismic risk;(2)the middle and south part of Red River fault zone is no longer independent as the southwest boundary of the central Yunnan block,but not with both sides The fault zone of Wuliangshan and Chuxiong Jianshui fault take on the role of block boundary,especially in the south section of Red River fault zone;(3)the south section of Red River fault zone is located in the transition zone between the central Yunnan block and the South China block,and the movement property has changed,showing the trend of left-hand strike slip movement.