HR: 0830h
AN: H11G-0952    [PDF]
TI: Determination of a Permeability-depth Curve for the Oregon Cascades Employing Numerical, Analytical, and Statistical Methods
AU: * Saar, M O
EM: msaar@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building 425 E. University Ave., Ann Arbor, MI 48109-1063 United States
AU: Manga, M
EM: manga@eps.berkeley.edu
AF: Department of Earth and Planetary Science, UC Berkeley, McCone Hall UC Berkeley, Berkeley, CA 94720-4767 United States
AB: We employ analytical and numerical models as well as statistical methods and signal processing techniques to study both pore-fluid pressure diffusion and coupled groundwater and heat transfer in the subsurface. Both processes are used to infer the large-scale vertical permeability distribution and other hydrogeologic parameters in the Oregon Cascades volcanic arc. Multiple temperature-depth profiles and their deviations from a linear(conductive) relationship provide insight into advective heat transfer and related groundwater flow patterns and velocities. In addition, the coupled modeling approach provides background heat-flow rates of 0.080 $<$ H $<$ 0.130 W/m$^2$ for the study region where heat flow is otherwise typically masked by cold groundwater recharge. We also infer regional scale groundwater recharge rates of about 1 m/year. Statistical, Monte Carlo, and signal processing techniques are used to investigate if seasonal groundwater recharge due to spring snow melt enhances earthquake occurrence after a pressure-diffusion related time lag, during summer. We find statistically-significant cross correlations between groundwater recharge and earthquake occurence at Mt. Hood, Oregon, with a time lag of about 151 days. This phase lag and a mean earthquake depth of about 4.5 km imply an average permeability of about $10^{-15}$ to $10^{-14}$ m$^2$ for a depth range of about 2 $<$ z $<$ 5 km. Combining the heat-advection study, the hysroseismicity study, and other investigations allows us to infer permeability, k, as a function of depth, z. We suggest approximately log(k) = -13 to log(k)= -18.3 m$^2$ for z=0 to z=12 km, respectively, for the Oregon Cascades. Our results agree with values compiled by Manning and Ingebritsen (Rev. Geophys., 1999) for continental crust in general. However, we suggest an exponental k(z)-curve for z $<$ 0.8 km and a power law relationship for z $>$ 0.8 km.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1878 Water/energy interactions
SC: Hydrology [H]
MN: 2003 Fall Meeting