HR: 0800h
AN: G21A-0125    [Abstracts]
TI: Ground motion measurement in the lake Mead (Nevada, USA) area by temporal analysis of multiple interferograms.
AU: * Cavalie, O
EM: cavalie@geologie.ens.fr
AF: ENS, 24 rue Lhomond, Paris, 75231 France
AU: Doin, M
EM: doin@geologie.ens.fr
AF: ENS, 24 rue Lhomond, Paris, 75231 France
AU: Lasserre, C
EM: lasserre@geologie.ens.fr
AF: ENS, 24 rue Lhomond, Paris, 75231 France
AU: Briole, P
EM: briole@ipgp.jussieu.fr
AF: IPGP, 4 place Jussieu, Paris, 75252 France
AB: SAR interferometry has proven to be a reliable method for detecting small displacements due to ground subsidence. In this study, we propose to measure ground motion around the lake Mead (Nevada, USA) using InSAR. This artificial lake has been filled with water in 1935. An earlier studie, based on levelling measurements, has shown that the lake impoundement has induced a subsidence of 17 centimeters (Kaufmann et al., 2000). This relaxation process is analogous to the postglacial rebound, but at a smaller scale. To quantify the deformation and constrain the crust and mantle rheological parameters in the lake area, we have analysed multiple interferograms (245) based on 45 ERS images between 1992 and 2001. The interferometric phase contains information about deformation occurring between two satellite passes, as well as satellite orbits errors, topographic, and atmospheric artefacts. The topographic signature is removed using the 3-arc seconds SRTM data. To correct for orbital errors, we remove a best fitting linear ramp. Atmospheric artefact, in our interferograms, are mainly due to the variation of water vapor vertical stratification between the two passes. This results in a interferometric phase correlation with altitude which we remove by minimization. These corrections are then refined through an iterative procedure and validated using data from global atmospheric models. Corrected interferograms are then inverted to solve for deformation using a method based on the large spatial coverage of coherent pixels, allowing to strengthen the signal to noise ratio (Schmidt and Burgmann, 2003). This data inversion provides a time series of the expected deformation in the lake Mead area. The analysis of the deformation evolution during the period covered by the ERS satellites (1992-2001) shows a correlation between the vertical motion and the water level changes. So, we observe a subsidence of up to 1.5 cm between 1996 and 1998, followed by an uplift due to the drop of the water level after 2000. Apart from this deformation, we observe a local anticorrelated movement in a 20*10 km area located North of the lake with a significative uplift of 1.2 cm during the period of the lake area subsidence. Finally, the west side of our ERS scene shows a small subsidence located in Las Vegas. This ground motion is independant of the lake water load variation.
DE: 1208 Crustal movements--intraplate (8110)
DE: 0933 Remote sensing
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting