HR: 0800h
AN: H11D-0322    [Abstracts]
TI: Response of Water Levels in Devils Hole, Death Valley National Park, Nevada, to Atmospheric Loading, Earth Tides, and Earthquakes
AU: * Cutillo, P A
EM: paula cutillo@nps.gov
AF: Paula A. Cutillo, National Park Service, Water Resources Division, 1201 Oakridge Drive, Suite 250, Fort Collins, CO 80525 United States
AU: Ge, S
EM: ges@colorado.edu
AF: Shemin Ge, Department of Geological Sciences,University of Colorado, Boulder, CO 80309 United States
AB: Devils Hole, home to the endangered Devils Hole pupfish (Cyprinodon diabolis) in Death Valley National Park, Nevada, is one of about 30 springs and the largest collapse depression in the Ash Meadows area. The small pool leads to an extensive subterranean cavern within the regional Paleozoic carbonate-rock aquifer. Previous work has established that the pool level fluctuates in response to changes in barometric pressure, Earth tides and earthquakes. Analyses of these fluctuations indicate that the formation is a sensitive indicator of crustal strain, and provide important information regarding the material properties of the surrounding aquifer. Over ten years of hourly water-level measurements were analyzed for the effects of atmospheric loading and Earth tides. The short-term water-level fluctuations caused by these effects were found to be on the order of millimeters to centimeters, indicating relatively low matrix compressibility. Accordingly, the Devils Hole water-level record shows strong responses to the June 28, 1992 Landers/Little Skull Mountain earthquake sequence and to the October 16, 1999 Hector Mine earthquake. A dislocation model was used to calculate volumetric strain for each earthquake. The sensitivity of Devils Hole to strain induced by the solid Earth tide was used to constrain the modeling. Water-level decreases observed following the 1992 and 1999 earthquakes were found to be consistent with areas of crustal expansion predicted by the dislocation model. The magnitude of the water-level changes was also found to be proportional to the predicted coseismic volumetric strain. Post-seismic pore-pressure diffusion, governed by the hydraulic diffusivity of the aquifer, was simulated with a numerical model using the coseismic change in pore pressure as an initial condition. Results of the numerical model indicate that factors such as fault-plane geometry and aquifer heterogeneity may play an important role in controlling pore pressure diffusion in the Devils Hole area.
DE: 7260 Theory and modeling
DE: 3210 Modeling
DE: 1829 Groundwater hydrology
DE: 1249 Tides--Earth
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting