GNSS Analysis Of Present Crustal Movement And Tectonic Deformation In North China

The North China?Its latitude and longitude range is 30°-42°N,104°-124°E?region is located in the eastern part of mainland China.Since the Mesozoic,it has experienced large-scale crustal extension and lithospheric thinning.It has a complex tectonic background and frequent earthquakes.Since the 1990s,rich GNSS monitoring activities have been carried out in North China,providing high-precision quantitative observation data for understanding crustal movement and tectonic deformation in this area.In this paper,using the GNSS velocity field data in North China,the multi-dimensional wavelet analysis method is first used to calculate the regional strain rate field.The distribution characteristics of the shear strain rate,surface expansion rate and rotation rate are analyzed in combination with the active tectonic background of the study area and the distribution of the focal mechanism solution..Then,based on the existing geological seismic fault zone data,the North China area is divided into blocks,using the DEFNODE negative dislocation model,the grid search algorithm and simulated annealing algorithm are used to invert the Euler vector,motion velocity and fault slip rate of the main block And other parameters.Finally,combining the strain rate field and the motion parameters of each block in North China,the structural deformation and crustal motion characteristics are analyzed to provide data for the assessment of earthquake risk.?1?The research results show that the North China region moves from west to east,from north to south,and there is a clockwise deflection trend.The horizontal movement characteristics of the block boundaries change significantly,and the movement of each block is also very different;?2?The distribution of strain rate in North China is consistent with the long-term tectonic background and seismic distribution in this area.The shear strain rate,surface expansion rate and rotation rate in most areas are less than 0.5×10^-8/a.The high strain rate areas are mainly concentrated near the block edge or block boundary fault zone,and the strain rates in other areas are relatively small.In areas where the higher values of the surface expansion rate and the shear strain rate coincide,that is,the parts where the strain field changes significantly,the probability and risk of earthquakes are high.Among them,the Yinchuan fault in the west of the Ordos block and the Zhangjiakou-Penglai fault in the north of the North China Plain block have relatively high strain rate and rotation rate,reflecting the energy accumulation related to earthquake breeding;?3?Each block in North China rotates clockwise,and the rotation rate is below0.3°/Ma.Each block and the surrounding blocks show eastward movement,but there is a slight difference in north-south movement.Among them,the maximum eastward velocity of the South China block is 6.9 mm/a,and the minimum velocity of the Yanshan block is 2.2 mm/a.The eastward velocity of each block in North China is about 5 mm/a.Among them,the Ordos block and South China block do not undergo large-scale structural deformation and are relatively stable moving blocks.The blocking depth of each fault is 15km.On the whole,the sliding rate of faults in North China is relatively small,and the main slip is slip.The Qinling-Dabie Mountain,Zhangjiakou-Penglai fault zone and the northern marginal fault zone of Ordos are left-lateral strike-slip,and the other five fault zones show right-lateral strike-slip.The fault-prone sliding rate in North China is generally below 1 mm/a;?4?According to the analysis of the GNSS velocity field and the motion parameters of each block in North China,the present structural deformation and crustal movement in North China present block characteristics.The weak boundary within the block tectonic activity is intense,but the North China Plain can be divided into three secondary active blocks:Yuhuai,Jilu and Taihangshan secondary active blocks.Because of the difference in force,different blocks and faults will have different states of motion such as tension,squeezing,and sliding,but the motion rate and Euler vector of each block and fault are relatively small.After comparing the research results of the block division by the geological and seismic tectonic background and the activity of the block fault zone discovered by GNSS research,it is found that the conclusions obtained by the two are basically the same.