HR: 0800h
AN: G51C-0844    [Abstracts]
TI: InSAR Reveals a Potpourri of Deformation Signals in the Yucca Mountain -- Amargosa Valley -- Death Valley Region, Southwestern Nevada/Southeastern California
AU: * Katzenstein, K W
EM: kkatzens@unr.nevada.edu
AF: Department of Geologic Sciences and Engineering, University of Nevada, M/S 172, Reno, NV 89557 United States
AU: Bell, J W
EM: jbell@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, M/S 178, Reno, NV 89557 United States
AB: InSAR studies have revealed a variety of surface deformation signals attributed to several causes in the Yucca Mountain -- Amargosa Valley -- Death Valley region. This study utilizes 26 ERS 1 and 2 scenes to produce 34 interferometric pairs that cover the period of 1992 - 2000. Prominent signals that have been previously studied include the 1992 Little Skull Mountain Earthquake and groundwater subsidence in the Pahrump Valley (Lohman et al., 2002, and Utley, 2005). Several subsidence signals (2.5 -- 3.5 cm) present within Amargosa Valley represent aquifer response in close proximity to local groundwater withdrawal. Observed groundwater level declines in the vicinity of the subsidence bowls are also present. However, signals near Amargosa Flat and Ash Meadows National Wildlife Refuge appear to be a more complex regional aquifer response related either to distant groundwater use or other hydrologic processes related to the abundant spring activity in the area as groundwater levels have remained fairly steady in these regions. A subsidence signal at Frenchman Flat, within the Nevada Test Site, shows approximately 2 cm of subsidence with the majority occurring between 1998 and 2000. Groundwater use in this area was actually lower during this time period than during the previous six years covered by this study, and monitoring wells suggest a relatively constant depth to groundwater with no notable trend up or down. This suggests another mechanism behind the subsidence, including the possibility that three nuclear blast centers located within the subsidence bowl have altered groundwater recharge conditions in the area. The signal with the largest magnitude is related to mining activity at the Bullfrog Mine located west of Beatty, NV. At this location, as much as 8 cm of subsidence, occurring between 1995 and 2000, is centered on the eastern edge of the mine site and extends into the bedrock to the northeast. GPS data (Bennett et al, 2003 and Wernicke et al, 2004) suggest that a velocity contrast of approximately 3.5 mm/yr exists between the Yucca Mountain Block and the Furnace Creek Fault in eastern Death Valley. Unit vector values for the SAR data suggest that this velocity contrast translates to a line of sight (LOS) change of approximately 0.90 -- 0.95 mm/year. Therefore, over the eight year study period, a total LOS change of approximately 0.7 -- 0.8 cm is theorized. Although this LOS change is large enough to be detected using InSAR, this study was unable to detect and locate a signal that could be confidently attributed to this velocity contrast. This is likely due to the wide aperture over which the shear is acting, as well as topographic interference inherent in InSAR studies in regions of variable relief. This study was supported by NASA grant NAG 13 -- 02017.
DE: 1211 Non-tectonic deformation
DE: 1829 Groundwater hydrology
DE: 6924 Interferometry (1207, 1209, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005