Study On Vertical Crustal Motion In Chinese Mainland And Typical Areas Based On Continuous GPS

The study on vertical crustal movement(including crustal long-term linear motion and seasonal motion)has important theoretical and practical value.Firstly,the long-term crustal vertical velocity field can directly reflect the dynamic characteristics of the Earth's surface,and its precise acquisition has great significance to regional economic construction and social development;Secondly,an understanding ofseasonal vertical crustal motions(SVCM)supports accurate measurement of the station altitude and improves the stability of the terrestrial reference frame at seasonal scale.Thus,SVCM is closely related to the change of the regional geophysical fields,and can be used to monitor mass variations of regional snow,groundwater and so on.Compared with other vertical crustal motion monitoring methods(such as InSAR and level),continuous GPS(CGPS)has the advantages of high temporal resol ution,low cost,which can record the SVCM precisely and identify the temporal uneven deformation of vertical crustal motions.With the construction of CGPS network established in Chinese mainland(e.g.the Tectonic and Environmental Observation Network in China),a large number of long-term observations have been accumulated,which provides good data support for the analysis of vertical crustal motion in Chinese mainland.Therefore,this paper first analyzed the large spatial scale of vertical crustal motions in Chinese mainland.Secondly,Yunnan(with significant SVCM)and Tianjin(with significant linear vertical motion)were selected as the research areas,and relevant researches were carried out based on the analysis of the more intensive GPS continuous observation data in this two typical regions.The results are as follows:(1)Vertical crustal motions(linear and seasonal motions)in Chinese mainland were assessed from 235 CGPS stations observations over the period 2010 to 2016.The results demonstrated significant SVCM in Chinese mainland with annual cyclic movements as the dominant pattern(the mean annual cyclic amplitude is 4.8mm).The SVCM in Chinese mainland exhibited regional differences due to different influencing factors of SVCM in different regions;(2)The vertical crustal linear motion in Chinese mainland derived from CGPS is relatively stable during the period 2010-2016,and the absolute values of velocities on most stations are within 6mm/yr.On the whole,the linear motion in Chinese mainland can be characterized by inheritance movement,that is,"mountains rise,while basins and plains decline";(3)SVCM in Yunnan are assessed from 27 CGPS stations observations over the period 2010-2015.The results demonstrate that during data processing,the variations in the amplitude of annual verticalcyclic crustal movements in Yunnan caused by the differences in the reference frame point and reference frames did not exceed 1 mm.Annual vertical cyclic crustal movements in Yunnanhave two characteristics:?these annual cyclic movements exhibit a high degree of spatial uniformity as a whole;? taking the Jinshajiang-Red River Fault as the boundary between western and eastern Yunnan,some spatial differences in SVCM exist across regions,the annual vertical cyclic crustal movements in western Yunnan is more significant than that in eastern Yunnan;(4)GPS seasonal vertical time-series movement in Yunnan shows strong consistency with GRACE(Gravity Recovery and Climate Experiment)data result,providing further indication that regional deformation exerts a dominant effect on the GPS vertical time-series.Over the period 2010-2015,the Yunnan area featured substantial precipitation that shows significant annual periodicity and a strong correlation with the GPS vertical time-series.Therefore,it is considered that the regional deformation caused by rainfall is the main reason for the vertical cyclical movement of Yunnan crust,and the seasonal precipitation is therefore concluded to be the regional dominant factor that governs vertical cyclic crustal movements in this area.Differences in precipitation,underground medium parameters and crustal structure between western and estern Yunnan(i.e.across the Jinshajiang-Red River Fault)result in a greater magnitude of SVCM in western Yunan compared to that in eastern Yunnan.(5)Linear vertical motions rates of Tianjin are assessed from 22 CGPS stations observations over the period 2006-2017.The results demonstrate that the northern part of Tianjin shows a low-speed uplift of about 2mm/yr,and the other areas are rapidly sinking due to human activities(such as groundwater exploitation),with a maximum subsiding rate of 79mm/yr.GPS continuous observation data show that sink of some stations is not identical in time,the maximum of annual variations in vertical timeseries on most stations are found in 2011 or 2015.