Crustal Deformation In Shanxi Province Based On High Precision GPS

Shanxi Province is located in the middle of the North China Plate,the southeast edge of the Ordos block,the hinterland of the Loess Plateau,with complex terrain,taihang Mountain in the east and Luliang Mountain in the west,and an asymmetric basin in the middle,roughly in the shape of "S",which runs through the whole West of the Mountain from north to south.Moreover,the geological structure is also very special,showing a uplift area on the whole,while the internal structure is complex and uneven,including both fault depression and uplift.It is an area prone to geological disasters.At the same time,as a resource-based province,perennial coal and bauxite mining has caused serious secondary geological disasters.As one of the strongest seismic belts in North China,shanxi fault depression plays an important role in the tectonic activity pattern of north China,which can reflect the strength and dynamic changes of tectonic activity in north China to a certain extent.In recent 20 years,with the development of earth science and GPS station of encryption,"crustal movement observation network of China" and "China environmental structure monitoring network" upgrade,site density and data accuracy has been greatly improved,for geodesy and geodynamics research emerged many new theory method.Combining previous research methods and making full use of the advantages of GPS geodetic,solve the problem of crustal movement and tectonic activities.This paper collected the tectonic background,main fault characteristics and seismic activity characteristics of Shanxi fault depression belt and its surrounding areas.Based on the observation data of "China continental Environmental structure Monitoring Network","North China Geophysical Field" and "Shanxi GPS Seismic Monitoring network",High precision GPS data processing software GIPSY(V6.0)was used to process the velocity field of Shanxi fault depression zone under reference frame ITRF2014,and three-dimensional coordinate time series analysis of the site was carried out to describe its corresponding motion characteristics.On this basis,in order to make the analysis of crustal deformation in the study area more hierarchical,the crustal strain characteristic parameters of shanxi fault depression zone are calculated,including the main strain rate,surface expansion rate and shear strain rate.Through analysis,it can be concluded that the whole Shanxi fault depression belt moves towards SE in the horizontal direction,the velocity is 34.07mm/a;and the movement intensity on the east and west sides is less than that of the inner fault depression basin.In the vertical direction,the whole subsidence trend is presented,but the subsidence rate is different,the average rate was 25.62mm/a,and the surrounding mountains mainly show continuous rise,the average rate was 25.39mm/a.The main research contents and achievements of this paper are as follows:(1)The geological tectonic background,main fault characteristics and seismic activity data of Shanxi Province and its surrounding areas are collected.Huashan piedmont fault presents different characteristics under different geomorphic and structural backgrounds.Luoyunshan piedmont fault is a fault zone with EW-NNE strike normal fault and dextral strike-slip nature.Zhongtiaoshan piedmont fault is NE-SW trending,Huoshan piedmont fault is near NW trending,Taigu fault and Jiaocheng fault are NE-NW trending,Wutai Piedmont fault is NNE trending,northern piedmont fault of Hengshan is NE-SW trending normal fault,Liulingshan piedmont fault is NE trending.After wenchuan earthquake in 2008,the fault depression belt of Shanxi Province entered the high frequency of earthquakes.(2)On this basis,we selected long-term GPS observation data with high precision and high spatial and temporal resolution of continuous stations and surrounding areas in Shanxi Province from 1996 to 2021.Data processing software such as GIPSY was used to obtain horizontal and vertical velocity field maps of the study area under the framework of ITRF2014.On the whole,the movement direction of Shanxi fault depression belt and its surrounding areas shows a trend of ES direction change,the surrounding mountainous areas and secondary uplift mainly show a continuous rise,the average rate was 25.39mm/a,and the central basin mainly shows a general characteristic of decline,but the decline rate is different.(3)There may be some errors in the coordinate time series obtained by using PPP method,among which some obvious systematic errors and periodic errors need to be eliminated according to their own characteristics and processed by wavelet transform to obtain more accurate coordinate time series.(4)Because the Shanxi fault depression zone is part of the Eurasian plate,the movement of the stations in the study area is included in the movement of the Eurasian plate itself,and the movement mode of the Eurasian plate will affect the local movement mode between the GPS stations in the plate.In order to highlight the crustal deformation characteristics of the Shanxi fault depression belt and its adjacent areas,the euler vector method was used to remove the velocity background field of the Eurasian plate and obtain the velocity field of the Shanxi fault depression belt and its surrounding areas relative to the Eurasian plate and the Ordos block,which reflects the consistent and different movement characteristics of the fault depression belt around the Ordos block.(5)The methods for calculating the three strain rates are briefly introduced,including the principal strain rate,plane strain rate and shear strain rate,the principal strain rate varies between 2.87-27.49nano-strain/a,the maximum surface expansion rate is 28.93nanostrain/a,and the maximum surface compression rate is 22.74 nanostrain/a.The maximum shear strain rate is 38.07nano-strain/a,indicating that the shanxi fault depression zone is characterized by NE-Nee compression and NW extension.