Analysis Of Crustal Deformation And Strain Characteristics In Yunnan Area

GNSS measurement technology can not only detect the surface displacement and deformation caused by earthquake,but also the tectonic movement deformation,seismogenic deformation,post-earthquake deformation and other minor tectonic deformation.It has become a powerful means to observe the crustal movement at present.Based on GNSS observation data,crustal deformation and strain information are extracted to analyze and study regional crustal strain characteristics and distribution rules,which is conducive to understanding the mechanism and development history of crustal tectonic movement and is of great significance for further research on seismic dynamics.In this paper,GAMIT/GLOBK software was used to calculate the observation data of 45 consecutive GNSS benchmark stations in Yunnan from 2015 to 2019,and the least-squares collocation method was adopted to obtain the crustal deformation and strain characteristics in Yunnan,and the relationship between crustal deformation and earthquakes in Yunnan from 2015 to 2019 was analyzed by combining the seismic information of magnitude 5.0 and above in Yunnan.The research contents and achievements of this paper are as follows:(1)The principle of GNSS measurement and the theoretical method of data solution are introduced in detail,as well as the method of strain field calculation.The main methods include multi-surface function fitting,spherical wavelet and least square configuration,and the least square configuration method is introduced in detail.(2)Based on the observation data of 45 GNSS benchmark stations running continuously in Yunnan from 2015 to 2019,the velocity field of Yunnan under the framework of ITRF2014 and the velocity field after deducting Euler rotation vector were calculated.The results show that under the framework of ITRF2014,the horizontal motion velocity in Yunnan region rotates in the southeast direction as a whole.There are obvious differences in relative motion in Yunnan,the relative motion in central and western Yunnan is weak,the relative motion at the junction of Sichuan and Yunnan is more violent,and the Xiaojiang fault zone presents significant sini-rotation characteristics,among which the sini-rotation characteristics at the southern end of The Xiaojiang fault zone are more severe than that at the northern end.(3)Based on the velocity field after deducting Euler rotation vector,the kriging interpolation method was used to interpolate the velocity of the station,and the least square collocation method was used to calculate the strain field in Yunnan region.The results show that the residua of the measured speed and fitting speed at the site are mostly within 1mm(except the residua of one site is 1.3mm),indicating the validity and reliability of the calculation method in this paper.Can be seen from the obtained strain parameters in Yunnan region,Yunnan region face inflation general alternates tension and compression phenomenon,that the earth's crust in Yunnan region of complex stress,tectonic movement is active,including tensile strain is the most prominent place in Muli-Yan Yuan area,compressive strain is the most prominent place in Tonghai-in Mengzi area;The maximum shear strain in Yunnan region is mainly divided into two high value zones,which are distributed along the Lijiang-Xiaojinhe and Xiaojiang fault zones,among which the maximum shear strain high value zone is located in the Kunming-Tonghai area,and the shear strain accumulation in other areas is low,indicating that the shear deformation is weak.(4)To get the velocity field and strain field in Yunnan before the earthquake of magnitude 5.0 and above in Yunnan form2015 to 2019 by the least square method.the results show that : it occured that part site accelerated sharply movement before the Changyuan,Yunlong,Yangbi,Tonghai earthquake,it showed that the relative balance of the motion state is broken,which induced earthquake;Before the Changning earthquake,the site at the junction of Sichuan and Yunnan moved from the chaotic motions into a uniform accelerated motion to southwest direction,however,movement range is not large relative to other site;There was not obvious anomaly characteristics of the site movement before the Mojiang earthquake;Accelerated motion characteristics appeared at the partail site before Changyuan,Chang ning,Tonghai earthquake earthquake,the earthquake happened in the direction of site acceleration,it had occurred in surface expansion rate near zero value area;The acceleration movement of part of site significantly appeared before Yunlong,Yangbi earthquake,but the earthquake did not happen in the direction of motion of the site,Yunlong earthquake occurred in the maximum shear strain of high value area,but not the peak value area,the Yangbi earthquake occured in the high value area of maximum shear strain;Mojiang earthquake occurred in the edge of the high inflation rate value.(5)The analysis of the above seismic train shows that when some sites have accelerated large abnormal movement,it is necessary to pay attention to the possibility of earthquake occurring in the area with 0 value of surface expansion rate,high value of maximum shear strain or the edge of high value area in the movement direction of the site;When the strain accumulation in the region is too high and the strain value tends to decrease,attention should be paid to the risk of earthquake occurring at the edge of the region with high surface expansion rate.