Quantitative Analysis Of The Drivers Of The Guobu Slope Deformation Based On Time-series InSAR

The rockslide of the reservoir bank is one of the common types of landslides,and precipitation and water level fluctuations are two important factors affecting the stability of the reservoir bank landslide.Quantitative research on the response of the rockslide to precipitation and water level changes is of great significance for avoiding the occurrence of the landslide,warnings,disaster prevention,and reduction.The Guobu slope is an ancient rockslide on the upstream reservoir bank of the Laxiwa Hydropower Station,which was reactivated during the storage period in 2009.Therefore,this study used 103 Sentinel-1images provided by the European Space Agency’s Copernicus Earth Observation Program and SBAS-InSAR technology to obtain the deformation time series of the Guobu slope from September 2015 to December 2019.Based on this,a detailed deformation feature analysis of the Guobu slope area was carried out.To fully explore the information contained in the InSAR deformation time series,this paper used three kinds of wavelet transformation tools to extend the one-dimensional time deformation sequence to the two-dimensional timefrequency domain and quantitatively analyzed the correlation and response relationship between different areas of the Guobu slope and external driving factors such as precipitation and water level of the reservoir.The aim was to provide a scientific basis for deformation warning,mechanism research,and stability evaluation of rockslides in the Guobu slope area.This paper obtained the following three conclusions through experiments:(1)The spatiotemporal characteristics of the Guobu slope deformation.The SBASInSAR deformation results show that the maximum deformation area is located at the edge of the Guobu slope platform,and the deformation rate of the top platform area and the slope foot area near the water surface are roughly equal.There are obvious spatial differences in the deformation rate,showing the motion mode of the upper part toppling with tearing damage and the down part shallow creep deformation.The average deformation rate and the cumulative deformation map do not show obvious expansion of the landslide boundary and deformation range,indicating that the deformation of the Guobu slope is a holistic motion.(2)Qualitative analysis of deformation driving factors.Three characteristic points,P1,P2,and P3,were selected on the surface of the slope,and linear and nonlinear deformation data for each point were separated by the least-squares linear fitting method.It was found that the nonlinear deformation amplitude changes of the high position area P1 at the edge of the platform and the low position area P2 at the foot of the slope are roughly the same,and the nonlinear deformation amplitude of the platform area P3 is smaller,indicating that the top platform is relatively stable.The combined analysis of nonlinear deformation and external precipitation and water level shows that there are four amplitudes in P1,and there is a good response relationship between precipitation and water level.P2 and P3 only have a certain amplitude response change from January 2016 to March 2017 and from June 2018 to March 2019.The relationship between the images can only qualitatively explain that the deformation of the Guobu slope is jointly driven by precipitation and water level and has a certain lag.(3)Quantitative analysis of deformation driving factors.Through the joint analysis of nonlinear deformation in regions P1,P2,and P3 and external precipitation and reservoir water level data using three types of wavelet transformation tools,the results show a positive correlation between P1,P2,and precipitation,and the deformation in the two regions lags behind precipitation by approximately 70 days,indicating that the sliding surface depths in the two regions are roughly equivalent.P1 and P2 exhibit a negative correlation with changes in reservoir water level,and the deformation in the two regions lags behind the changes in reservoir water level by 80 and 20 days,respectively.This may be because the P2 region is located at the foot of the slope where there is a good pathway for underground water and pore water,leading to a more rapid deformation response.The relationship between the P3 region and precipitation and reservoir water level is difficult to determine,and there may be other influencing factors.Additionally,the normalized wavelet coherence values indicate that precipitation contributes more to deformation than changes in reservoir water level...