InSAR Time Series Monitoring And Mechanism Analysis Of Land Subsidence In Shenzhen Area From 1997 To 2020

Since China's reform and opening up,the ground subsidence disasters in Shenzhen have been increasing.However,it is still unclear about the land subsidence mechanism and evolution law of land subsidence in Shenzhen.In response to this problem,this paper uses InSAR technology and SAR satellite data from 1997 to 2020 in Shenzhen to obtain the ground deformation rate field in Shenzhen.At the same time,the accuracy of the ground deformation results extracted by different satellites was evaluated,and the reliability of the ground deformation detection results of InSAR was demonstrated.Then based on the InSAR detection results of land subsidence,combined with land use changes,tectonic activities,engineering construction,quaternary strata,changes in precipitation,groundwater dynamic changes and other factors,this paper studies the temporal-spatial changes of land subsidence and the mechanism of land subsidence in Shenzhen.The main work and conclusions of this paper are:(1)Based on InSAR technology and SAR images of different periods from 1997 to 2020,the deformation field in Shenzhen area is extracted.The results show that from 1997 to 1998,large areas of land subsidence occurred in the southeast of Baoan District,the central part of Nanshan District,the central and western part of Futian District,and Luohu District,the maximum settlement rate is-150.65 mm/year,these subsidence areas form the"Shenzhen-Hong Kong Subsidence Belt".(2)In order to explore the difference in the evolution of land subsidence before and after land use change in Shenzhen,the results of land use change in Shenzhen from 1997 to 2020were extracted and compared with land subsidence.The results show that land subsidence has a good correlation with the temporal and spatial evolution of land use change.Take Shenzhen Bao'an District as an example.Between 1997 and 2010,the area of construction land in Bao'an District increased from 136.28 km~2 in 1997 to 281.12 km~2 in 2010,The water area of55 km~2 and the vegetation area of 91 km~2 are turned into construction land,and these newly added building sites have monitored various degrees of settlement.From 2010 to 2020,as land use changes in Bao'an District of Shenzhen tend to stabilize and the stratum gradually consolidated,the land subsidence area began to decrease.(3)In order to further the impact of urban expansion on land subsidence in the area,the settlement sequence analysis and tectonic movement analysis are carried out.The results show that urban expansion has caused regional land subsidence to a large extent.Taking the Yangtaishan fault zone as an example,when there was no large-scale development in the early stage,the average deformation rate along the Yangtaishan fault zone was 6.04 mm/year.However,along the fault zone is gradually developed as construction land,and the surface deformation along the Yangtaishan fault zone shows a sinking trend.(4)In order to explore the influence of the Quaternary strata on land subsidence in the Shenzhen area,hydrogeological analysis was carried out based on geological drilling data.The results show that,due to the characteristics of large void ratio and high compressibility in the loose layers widely distributed in the stratum in Shenzhen area,settlement may be induced during the construction of the project.In addition,through the gray correlation analysis method,it is found that the minimum gray correlation degree between ground deformation and precipitation change is 0.60,and the maximum is 0.75.The minimum gray correlation degree between ground deformation and groundwater dynamic changes is 0.68,and the maximum is 0.85.It shows that the land subsidence rate decreases during the period of increasing precipitation.One of the reasons for this phenomenon may be that when the rainy season comes,the underground loose layer absorbs large amounts of water and swells in contact with water,alleviating ground subsidence.Another reason may be that the rainy season brings abundant surface water,which supplements the groundwater to a certain extent.As the groundwater level rises,the ground shows a rising trend.