HR: 1340h
AN: G13A-0789    [Abstracts]
TI: Post-seismic deformation across the central Nevada Seismic Belt, USA, and rheology of the lithosphere.
AU: * Gourmelen, N
EM: ngourmelen@rsmas.miami.edu
AF: RSMAS, University of Miami, 4600 Rickenbacker causeway, Miami, FL 33149 United States
AU: Amelung, F
EM: amelung@rsmas.miami.edu
AF: RSMAS, University of Miami, 4600 Rickenbacker causeway, Miami, FL 33149 United States
AB: We investigate the post-seismic surface deformation in the Central Nevada Seismic Belt (CNSB), located at the south western end of the Basin and Range, USA. The CNSB was the location of major normal and strike-slip earthquakes in 1915 (Pleasant Valley M7.6), 1932 (Cedar Mountain M7.2) and in 1954 (Fairview Peak M7.2 & Dixie Valley M6.8). These earthquakes represents an interesting set of events to study post seismic deformation because of their magnitude, number and temporal repartition. Moreover, GPS measurement over the CNSB shows abnormal pattern, first the rate of present deformation is higher by ~2mm/yr in comparison with the quaternary strain rate obtained by paleoseismology, then, the GPS shows compressionnal pattern in an extensional context, which suggest transient post-seismic deformation following the earthquakes. We measure surface deformation in the CNSB using Interferometric Synthetic Aperture Radar (InSAR). We obtained 9 interferograms from 18 SAR images each covering four adjacent frames (~400 km in along-track direction), spanning 4-7 years using ERS SAR imagery acquired between 1992 and 2001. A precise displacement map obtained by stacking (averaging) the interferograms shows shortening of the distance between the ground and the satellite at a rate of ~2-3mm/yr (range change). The maximum range changes occur in the epicentral area of the 1915 Pleasant Valley, 1954 Fairview Peak and 1954 Dixie Valley earthquakes. We modeled the post-seismic deformation expected after the earthquakes using VISCO1D code (Pollitz F.) which allow to compute the surface deformation caused by viscoelastic relaxation within the lithosphere. We include the stress imposed by the four earthquakes, tested different lithosphere models and invert for the viscosity of both lower crust and upper mantle, elastic thickness and earthquakes magnitudes. We found that post-seismic deformation explain the observe deformation for an elastic thickness equal to the crustal thickness and a viscoelastic upper mantle with low viscosity value of ~2e18 Pa.s. Both abnormal high extension rate and compressionnal pattern measured by GPS are explained by our model for the post-seismic deformation.
DE: 7205 Continental crust (1242)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting