HR: 0800h
AN: G51C-0843    [Abstracts]
TI: Subsidence and Differential Surface Movement in the Upper Coachella Valley, California, as Indicated by InSAR
AU: * Wisely, B A
EM: bwisely@darkwing.uoregon.edu
AF: University of Oregon, 1272 University of Oregon, Eugene, OR 97403 United States
AU: Schmidt, D
EM: das@uoregon.edu
AF: University of Oregon, 1272 University of Oregon, Eugene, OR 97403 United States
AB: We present interferometric synthetic aperture radar (InSAR) results for the Coachella Valley, California, indicating land subsidence in the Upper Coachella Valley and regions of differential movement along faults east of San Gorgonio Pass. The Coachella Valley is a northwest trending basin, bounded to the east by the southern San Andreas Fault, to the west by the San Jacinto and Santa Rosa Mountains, and to the south by the Salton Sea. To the northwest, the Coachella Valley terminates in the San Gorgonio Pass stepover region, a contractional left step in the San Andreas Fault Zone, composed of a complex system of interacting faults. Several hundred differential interferograms are processed using SAR data from ERS1/2 satellite to image the deformation from 1992-2000. Up to 20 differential interferograms with temporal baselines greater than 3 years are stacked to reduce atmospheric noise. The greatest land subsidence rates indicated by the InSAR results can be seen in the Upper Coachella Valley, located along the Interstate 10 corridor. The maximum subsidence rates observed are ~5mm/yr from 1992-2000, and encompass the cities of Coachella, Indio, and Palm Springs. Subsidence rates of ~3mm/yr near Thousand Palms, Palm Desert and the Coachella Valley Preserve are also observed. We quantify the spatial and temporal distribution of subsidence in the region and compare subsidence time histories with well level data. Surface deformation is detected along the northwest trending, right-lateral Garnet Hill Fault (GHF) and along the sub-parallel, right-lateral Coachella Valley segment of the Banning Fault (CVBF). A deformation signal is detected along a section of the CVBF currently considered inactive due to a lack of surface geomorphic expression categorically associated with other active fault strands in the region. A range change of 1-1.5mm/yr is seen across each fault. The sign of the range change across these faults would correspond to left-lateral motion if it is assumed that the deformation is purely horizontal. This is contradicted by overwhelming geologic evidence for right-lateral motion. Considering only vertical motion, the range change suggests south-side up motion across each of these northwest trending faults, consistent with differential land uplift. The differential movement that is localized along regional faults is likely a hydrologically induced signal associated with the Whitewater recharge facility located near the intersection of the GHF and the CVBF. The differential movement shown by the distinct phase changes across the faults provides an opportunity to study fault zone porosity and permeability. Whitewater has been recharging the Coachella Valley Aquifer through percolation ponds since the 1970's to remedy overdraft-induced land subsidence. Our results suggest that the Whitewater facility has been unsuccessful at recharging regions of the Upper Coachella Valley Aquifer, as evidenced by continued subsidence observed in areas 15-45 km to the southeast.
DE: 1211 Non-tectonic deformation
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1719 Hydrology
DE: 1829 Groundwater hydrology
SC: Geodesy [G]
MN: Fall Meeting 2005