Research On GPS Non-tectonic Vertical Deformation

Since the 1990 s,with the rapid development of GPS technology,it has had a huge impact on national economic and scientific research.During the "11th Five-Year Plan" period,China invested in the construction of a major national scientific and technological infrastructure " Crust Movement Observation Network of China "(CMONOC).This network has built 260 GPS continuous observation stations and more than 2,000 short-term observation stations in China mainland and surrounding areas.CMONOC has built a high-precision,high-density monitoring network for China's mainland.CMONOC is mainly used to monitor the crustal movement,gravitational field changes,atmospheric tropospheric water vapor changes and ionospheric ion concentration changes in the Chinese mainland,in order to study the temporal and spatial changes of the crustal movement,the three-dimensional fine features of tectonic deformation.It also provide basic data and products for scientific issues such as the time and spatial change characteristics of crustal deformation in the short-term earthquake phase,the establishment and maintenance of modern geodetic reference systems,the large-scale water vapor transport model of heavy rains during the flood season,the dynamic changes of the ionosphere and space weather over China,.Since 2012,CMONOC have accumulated a large amount of observation data,and can obtain high-precision coordinate time series.These observational data can help scholars conduct deeper research in the fields of plate motion,coseismic deformation,and geodynamics.However,in addition to tectonic deformation in the GPS time series,interference from external factors such as land water mass loading,atmospheric loading,ocean tide loading,thermal expansion and other environmental loading,makes GPS observation time series contain a lot of non-tectonic deformation information.Although the periodic component of non-tectonic deformation will not have a fundamental impact on the extraction of large-scale tectonic deformation,it will have a periodic impact on the construction of a reference frame.It is the fundamental way to strip the non-tectonic deformation through the analysis of GPS continuous station observation non-tectonic data.It is an effective guarantee to improve the GPS observation results,and it also plays a vital role in the analysis of plate motion and geodynamic process.In this paper,the calculation methods and error sources of GPS observations are discussed,and 260 GPS continuous station observation data of the CMONOC are solved,and the three-dimensional coordinate time series data of the stations are obtained.The annual and semi-annual periodic signal of the vertical non-tectonic deformation are analyzed,and the vertical non-tectonic deformation periodic signal is extracted.The main research content and results of this paper are as follows:(1)The development status of GPS and the main research results of GPS non-structural deformation in recent years are summarized,and the research significance and research status of GPS non-structural seasonal deformation are reviewed.The influence of soil periodic deformation of the non-tectonic deformation of GPS continuous stations is discussed.(2)The calculation methods and error sources of GPS observations are discussed.The observation data of 260 GPS continuous stations in CMONOC were culculated,and the three-dimensional coordinate time series data of the stations are obtained.The annual signal and semi-annual signal of vertical non-tectonic deformation are analyzed.Moreover,annual signal of vertical non-tectonic deformation is extracted.(3)By calculated the atmospheric load deformation in China and surrounding areas,30 GPS continuous stations in the land network are corrected.The results show that atmospheric loading can explain about 9% of the annual periodic amplitude of GPS non-tectonic vertical deformation,and WRMS can decrease by 3% on average.Non-tidal ocean loading has a greater impact on coastal areas.With the increase in distance of inland areas,the non-tidal ocean loading impact gradually becomes smaller.The calculation results show that the vertical deformation of non-tidal ocean loading along the Bohai Sea and the Huanghai Sea can explain about 11% of the annual periodic amplitude of GPS non-tectonic,and the WRMS improvement effect is obvious,which can be reduced by 5% on average.However,the GPS non-tectonic deformation along the coast of the Donghai Sea and the Nanhai Sea has a low correlation with the non-tidal ocean load deformation,resulting in an increase in the amplitude of the GPS non-tectonic after correction,and the WRMS has not been improved.This may be related to the different impacts between open seas and enclosed seas.Open seas are more likely to be affected by storm surges and other complex effects.Therefore,it is not rigorous enough to use ocean bottom pressure to calculate non-tidal ocean loading.(4)The effect of thermal expansion on the non-tectonic deformation of GPS cannot be ignored.The effect of thermal expansion is divided into the monument and the bedrock which caused by the temperature.The monument is calculated by linear thermal expansion formula,and the result can explain the 5% annual periodic amplitude of GPS non-tectonic deformation.However,since all the GPS observation stations of the CMONOC are built in houses,and some houses provided heated in winter,the thermal expansion effect of most observation piers has been overestimated.Two bedrock thermal expansion models are compared and analyzed,the semi-infinite space thermal expansion model and the limited space sphere thermal expansion model.The limited space sphere thermal expansion model takes into account the thermal attenuation of the limited space and fixes the center of mass of the earth.The calculated result is larger than the semi-infinite space heat conduction model,and the physical meaning is clearer.(5)Based on the GRACE time-varying gravity field,the terrestrial water storage(TWS)load deformation is inverted.The results show that the TWS load deformation has a high correlation with GPS,and the correlation coefficient of the annual period term can reach 0.87 on average.At the same time,the nonlinear autoregressive model(NARX)was used to simulate the land water load deformation of 8 GPS continuous stations based on GRACE and GLDAS data.The land water load deformation value simulated by NARX can be corrected to reduce WRMS by 1%-30%.The correction effect can be improved by an average of 5% compared with GLDAS.(6)It focused on the the soil periodic deformation obtained by continuous observation of static leveling.It links the leveling results of Liqizhuang bedrock point with the vertical observation results of GPS continuous observation,and discusses the leveling results,static leveling and GPS.The relationship between leveling and GPS two different elevation systems is explained.Through the comparison with the leveling data,the reliability of the static leveling observation data is verified.And the accuracy of the continuous observation of the static leveling is higher.The soil periodic deformation can explain about 16% of the annual amplitude of CH01 station.And the WRMS of the GPS non-tectonic deformation can be reduced by about 4%.Obviously,the GPS non-tectonic deformation can be effectively corrected by the static leveling continuous observation results.This method is also the most effective method for correcting the periodic soil deformation at present.(7)Taking the Tianjin CORS network as the research object,the basic geological structure conditions of Tianjin are analyzed,and it is found that the thickness of the sedimentary layers on the north and south sides of the Baodi fault is different.The soil periodic deformation is only applicable to the area south of the Baodi fault at a small spatial scale.The soil periodic deformation can explain the 14% annual amplitude of non-tectonic deformation in Tianjin area.After correction,the WRMS of GPS vertical non-tectonic can be reduced by 2% on average.For the unimproved GPS continuous station,a comparative analysis of the groundwater level data near the site showed that in areas where groundwater was over-exploited which affected the soil periodic deformation.