HR: 11:35h
AN: G42A-06    [Abstracts]
TI: Ground Motion Measurement in the Lake Mead Area (Nevada, USA), by Temporal Analysis of Multiple Interferograms.
AU: * Doin, M
EM: doin@geologie.ens.fr
AF: Ecole Normale Supérieure Laboratoire de Géologie, 24 rue Lhomond, Paris Cedex 05, 75231 France
AU: Cavalie, O
EM: cavalie@geologie.ens.fr
AF: Ecole Normale Supérieure Laboratoire de Géologie, 24 rue Lhomond, Paris Cedex 05, 75231 France
AU: Lasserre, C
EM: lasserre@geologie.ens.fr
AF: Ecole Normale Supérieure Laboratoire de Géologie, 24 rue Lhomond, Paris Cedex 05, 75231 France
AU: Briole, P
EM: briole@ipgp.jussieu.fr
AF: Institut de Physique du Globe, place Jussieu, Paris, 75005 France
AB: SAR interferometry has proven to be a reliable method for detecting small displacements due to ground subsidence. In this study, we measure ground motion around the lake Mead (Nevada, USA) using InSAR. This artificial lake has been filled with water in 1935. An earlier study, based on leveling measurements, has shown that the load associated with lake impoundment has induced a delayed subsidence of 17 centimeters. This relaxation process has been argued to be due to viscous displacement in the uppermost mantle, analogous to the postglacial rebound, but at a smaller spatial scale and with a much lower viscous relaxation scale. To quantify the deformation and thus constrain the crust and mantle rheological parameters in the lake area, we analyse multiple interferograms (~280) based on 43 ERS images acquired between 1992 and 2001 and on 12 Envisat images acquired between 2003 and 2005. ERS-Envisat interferograms are performed to merge the two data sets in one time series. With baselines smaller than 300 m, all interferograms have a very good coherence due to the desert region. Most interferograms show strong atmospheric artefacts that are partly due to the variation of water vapor vertical stratification between two satellite passes. Tropospheric delay is computed for each interferogram using the correlation between phase and elevation far from the lake area. It is then inverted for each date of SAR images before interferograms correction. These corrections are validated using data from global atmospheric models (ERA40). Corrected interferograms are then inverted to solve for time series of the expected deformation in the lake Mead area . The linear inversion treats each pixel independently from its neighbours and use the data redundancy to reduce errors such as local decorrelations. Smoothing constraints added in the inversion efficiently eliminate local atmospheric artefacts. We obtain a time series of the expected deformation in the lake Mead area. The analysis of the deformation evolution during 1992-2005 the period shows a very good correlation between the ground motion and the water level changes. Our method allows to obtain a millimetric accuracy of a non linear deformation in time over a large spatial scale. In particular, we observe a subsidence of up to 1.7 cm between 1995 and 1998 due to a large water level increase, followed by an uplift due to the drop of the water level after 2000. Forward elastic and viscoelastic models of the ground subsidence response to surface load are compared to the spatial and temporal subsidence inferred from SAR interferometry.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
SC: Geodesy [G]
MN: Fall Meeting 2005