Depth dependence of permeability in the Oregon Cascades inferred from hydrogeologic, thermal, seismic, and magmatic modeling constraints (original) (raw)
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Geofluids, 2014
Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600-900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (k x /k z~1 0 4) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.
Heat flow in the Oregon Cascade Range and its correlation with regional gravity, Curie point depths
1990
New heat flow data for the Oregon Cascade Range are presented and discussed. Heat flow measurements from several deep wells (up to 2500 m deep), as well as extensive new data from industry exploration efforts in the Breitenbush and the Santiam Pass-Belknap/Foley areas are described. The regional heat flow pattern is similar to that discussed previously. The heat flow is about 100 mW m-2 in the High Cascade Range and at the eastern edge of the Western Cascade Range, It is about 40-50 mW m-2 to the west in the outer arc block of the subduction z e. in the high eat flow zone the heat flow is low at shallow depths in young volcanic rocks due to the high permeability ofthe rocks and the resultant rapid groundwater flow. Below a depth of 200400 m much of the area appears to be dominated by conductive heat transfer at least o 2-2.5 km depth. There are perturbations to the regional heat flow in the vicinity of the hot springs where values are up to twice the background. The gravity field in...
Seismicity induced by seasonal groundwater recharge at Mt. Hood, Oregon
2003
Groundwater recharge at Mt. Hood, Oregon, is dominated by spring snow melt which provides a natural largeamplitude and narrow-width pore-fluid pressure signal. Time delays between this seasonal groundwater recharge and seismicity triggered by groundwater recharge can thus be used to estimate large-scale hydraulic diffusivities and the state of stress in the crust. We approximate seasonal variations in groundwater recharge with discharge in runoffdominated streams at high elevations. We interpolate the time series of number of earthquakes, N, seismic moment, M o , and stream discharge, Q, and determine cross-correlation coefficients at equivalent frequency bands between Q and both N and M o . We find statistically significant correlation coefficients at a mean time lag of about 151 days. This time lag and a mean earthquake depth of about 4.5 km are used in the solution to the pressure diffusion equation, under periodic (1 year) boundary conditions, to estimate a hydraulic diffusivity of UW10 31 m 2 /s, a hydraulic conductivity of about K h W10 37 m/s, and a permeability of about kW10 315 m 2 . Periodic boundary conditions also allow us to determine a critical pore-fluid pressure fraction, PP/P 0 W0.1, of the applied near-surface pore-fluid pressure perturbation, P 0 W0.1 MPa, that has to be reached at the mean earthquake depth to cause hydroseismicity. The low magnitude of PPW0.01 MPa is consistent with other studies that propose 0.01 9 PP 9 0.1 MPa and suggests that the state of stress in the crust near Mt. Hood could be near critical for failure. Therefore, we conclude that, while earthquakes occur throughout the year at Mt. Hood, elevated seismicity levels along pre-existing faults south of Mt. Hood during summer months are hydrologically induced by a reduction in effective stress. ß
PROCEEDINGS-OCEAN …, 1995
In situ transmissivity of a hydrogeologically active fault zone within the Oregon accretionary prism was tested during Ocean Drilling Program (ODP) Leg 146. This experiment used an inflatable drill-string packer to conduct pressurized slug tests and constant-rate injection tests. Pressure responses during testing indicate dilation of fractures as a result of fluid injection. Consequently, test data allow examination of the transmissivity of an open fracture network. Analysis of pressurized slug-test data yields an average transmissivity of 1.0 × I0" 5 m 2 s" 1 , while recovery data from the constant-rate injection tests indicate transmissivities ranging from 4.7 to 9.2 × I0" 5 m 2 s~1. Test data indicate background borehole fluid pressure was 0.25 to 0.30 MPa greater than hydrostatic (approximately one-half lithostatic excess pressure) and indicate that fractures within the fault zone remain open at pressures approximately 0.315 to 0.325 MPa above hydrostatic.
2015
Warner Valley in southern Oregon (USA) is the site of a geothermal system that hosts several hotsprings in addition to Crump geyser – a geysering well that soon after being drilled in 1959 underwent frequent eruptions of boiling water. This, and thermochemical studies that estimate reservoir temperatures of 150°C, have prompted ongoing geological and geophysical investigations. Warner Valley is situated in a tectonically complex region in the northwest corner of the Great Basin - a basin and range province characterized by east-west extension. The regional geology consists predominantly of Neogene volcanics that have been faulted by a series of obliquely oriented NW and NNE-trending extensional faults. The valley forms an asymmetric graben, with the NNEtrending range front fault along the west Warner escarpement exposing over 600m of section. Warner Valley seems to be similar to other extensional geothermal systems in the Great Basin, which arise from deep circulation of meteoric wa...
Bulletin of Volcanology, 2000
Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity, little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of the Quaternary volcanic edifice. More than half of 18 focal mechanisms determined for these events are normal, and most stress axes deviate significantly from the regional stress field. We argue that these characteristics are most consistent with earthquakes in response to processes associated with circulation of fluids and magmatic gases within and below the base of the edifice.Circulation of these fluids and gases has weakened rock and reduced effective stress to the point that gravity-induced brittle fracture, due to the weight of the overlying edifice, can occur. Results from seismic tomography and rock, water, and gas geochemistry studies support this interpretation. We combine constraints from these studies into a model for the magmatic system that includes a large volume of hot rock (temperatures greater than the brittle–ductile transition) with small pockets of melt and/or hot fluids at depths of 8–18 km below the summit. We infer that fluids and heat from this volume reach the edifice via a narrow conduit, resulting in fumarolic activity at the summit, hydrothermal alteration of the edifice, and seismicity.