Surface Seasonal Mass Loading Changes And Vertical Crustal Deformation In North China From GPS?GRACE And Surface Loading Models Measurements

The solid earth is an elastic body,and the surface mass loading changes such as the atmospheric and hydrologic loading will lead to elastic loading deformation on the surface of the Earth.Since 1970 s,the groundwater has been extensively exploited in the North China Plain,and unrecoverable land subsidence in some areas has been occurred due to excessive exploitation of groundwater,which has seriously affected the socio-economic development of North China.Therefore,studying the surface mass loading changes and vertical crustal deformation in North China is of great significance for the rational development of groundwater and economic sustainable development.As an effective means of earth observation,the Global Positioning System(GPS)has a wide range of applications in the field of monitoring the Earth's crustal deformation with the improvement of its detection accuracy.The Earth Gravity Recovery and Climate Experiment(GRACE)has accumulated a large amount of scientific observation data since it lunched,and the time-varying gravity field information obtained by it has played an important role in studying the change of Terrestrial Water Storage.It can also be used to monitor the vertical crustal displacement caused by seasonal surface mass changes.Global Surface Load Models,including atmospheric,non-tidal ocean and terrestrial water storage loadings can reflect the effects of surface loading changes on vertical displacement of the Earth's crust.In this paper,30 continuous GPS observations stations in North China are used to analyze the seasonal surface mass loading changes and vertical crustal deformation,comparing with the GRACE model and the Surface Load Models results,and the GRACE model is used to improve the vertical velocity field in North China.The observation data of 30 continuous observation GPS stations from Crustal Movement Observation Network of China were collected,and the time series of each station based on ITRF2008 framework was obtained by GAMIT/GLOBK software.The empirical mode decomposition method(EEMD)is used to analyze the time series for nonlinear signals,and the annual signal,semi-annual signal and long-term trend are extracted.The crustal vertical displacement corresponding to the position of each GPS station was obtained by GRACE satellite gravity inversion.By using the Fourier power spectrum analysis of the vertical displacement time series obtained from the Surface Load Models,comparing with the GPS time series power spectrum,and the principle of the seasonal signal in the GPS time series is analyzed,which indicates that the seasonal signal was mainly caused by the change of surface loading.Comparing the GPS time series,GRACE mass loading deformation and global surface load model time series of 30 continuous observation GPS stations for more than 5 years observation time,it is found that all three measurements show obvious seasonal signal.For most GPS stations,the correlation is good.The average correlation coefficient between GPS and GRACE is 90%,and the maximum value is up to 99%,while the correlation coefficient between GPS and surface load models is 88.7%.The weighted root-mean-square(WRMS)reduction was calculated by deducting the GRACE/SLMs-derived seasonal deformation from the detrend GPS-derived time series.For GPS and GRACE,the mean WRMS reduction for all selected 30 stations is 58%,and the maximum is up to 85.18%,which indicates a good consistency of the seasonal vertical deformation between GPS and GRACE measurements,and the possibility by using the GRACE model to simulate the non-structural deformation of GPS observation signals is confirmed.However,the consistency between GPS and SLMs results is not so good,with a mean WRMS-reduction of 31%,which means that the consistency of the seasonal vertical information between GPS and SLMs measurements is not so good,and it is due to the fact that the global SLMs perform not good in North China.The vertical velocity field of 30 continuous observation GPS stations is estimated by using the maximum likehood estimation method,and the vertical velocity field based on the ITRF2008 framework is obtained.The seasonal land water loading signals in GPS signals are analyzed according to the surface vertical deformation rate obtained by GRACE model.The long term trend of the crustal vertical deformation measured by GRACE is not obvious,which means that its contribution for GPS result is very small.The crustal vertical deformation field is analyzed.It is concluded that the vertical crustal deformation in North China is closely related to its geomorphic features.In the plateau area and the orogenic belt area,it performed as crustal uplift,while it performed as subsidence in plain area.For example,Shanxi Plateau and Yanshan,where is on the west of the Taihang Mountains and is in the north of the North China,show a crustal uplift.The vertical crustal uplift rate of SXXX Station,SXGX Station and HEZJ Station is 1.57 mm./yr,2.97 mm/yr,1.08 mm/yr respectively.The TJBH station and the HECX station in the plain area show very high sedimentation rates of-17.67 mm/yr and-25.25 mm/yr,respectively,and the results of the above two sites reflect the land subsidence caused by the groundwater losing.