| The location of the Sichuan-Yunnan region is unique and geological disasters occur frequently.It is a hot spot for the study of China's modern crustal movement.With the rapid development of GPS technology,observation data with high temporal and spatial resolution have been obtained,providing technical support for the study of contemporary crustal movement.Based on the GPS observation data from 1999 to 2015 in the Crustal Movement Observation Network of China,this article analyzes the crustal movement characteristics in the Sichuan-Yunnan area and provides some conclusions for the earthquake research in this area.The specific research content and achievements are as follows:1.Using GPS observation data from 1999 to 2015 and processing by GAMIT/GLOBK software,the speed vector under the reference frame of ITRF2008 is obtained.Then through the Euler vector rotation,the relative Eurasian plate in Sichuan-Yunnan region is obtained from 1999 to 2001.2004 to 2007,2011 to 2013 and 2013 to 2015 GPS speed field.Through analysis,it can be found that the activities of various fault zones in the Sichuan-Yunnan region affect the horizontal movement of the crust,and the overall movement speed of the region decreases from north to south and from west to east.The Xianshuihe fault zone has a strong activity.The GPS velocity field in the fault zone changes from 10mm/a to 12mm/a,and the rate of motion decreases until becoming 8mm/a.The Longmenshan fault zone has a velocity field of 2 mm/a before the Wenchuan earthquake breaking.Since it is in the process of adjustment and recovery after the earthquake,the rate gradually decreases from 10 mm/a.Because of the combined effect of the Burma Arc diving and the Sichuan-Yunnan rhombus block wedging,the southwestern Yunnan region increases its velocity from 2mm/a to 4mm/a and then gradually decreased.2.Using the GPS speed field from 1999 to 2015,the maximum shear strain rate,surface expansion rate,and main strain rate from 1999 to 2001,2004 to 2007,2011 to 2013,and 2013 to 2015 are obtained through the least-squares configuration method.It can be obtained through analysis that the shearing activity of the Xianshuihe fault zone is strong,and the maximum shear strain rate appears in the southern segment of the fault,and the magnitude is about 24×10-8/a.The south section of the Longmenshan fault was in a low-strain region before the Wenchuan earthquake,and the strain value increased significantly after the earthquake,in which the main compressive strain rate increased to 12×10-8/a.The evolution of strain in the middle section of the Honghe fault is not obvious,while the evolution characteristics of the southern section and the northern section are significant.The south section of the Wuliangshan fault is in the boundary area between surface expansion and surface compression.At the same time,the maximum shear strain rate of the fault zone is greatly increased from 4×10-8/a to 20×10-8/a,and then gradually decreased to 8×10-8/a.In order to further investigate the stress distribution of the Honghe fault and the Qujiang fault zone,the tectonic stress field in the northwestern Yunnan was established using finite element numerical simulation method.The simulation results show that the north section of the middle section of the Honghe fault and the north section of the Qujiang fault are the low-tensile areas with the maximum principal stress.Simultaneously with the southward effect of the middle block of the central Yunnan block and the regional tectonic setting,the maximum principal stress of the middle section of the Honghe fault on the side presents a distribution characteristic that is parallel to the tensile elongation.Therefore,the crustal movement in the middle section of the Honghe fault and the southern section of the Wuliangshan fault is complex and deserves attention. |
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