Seismicity induced by seasonal groundwater recharge at Mt. Hood, Oregon

Details Seismicity induced by seasonal groundwater recharge at Mt. Hood, Oregon Seismicity induced by seasonal groundwater recharge at Mt. Hood, Oregon

Sep 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003e%26psl.214..605s&link_type=abstract

Earth and Planetary Science Letters, Volume 214, Issue 3-4, p. 605-618.

Mathematics

Logic

27

Scientific paper

Groundwater recharge at Mt. Hood, Oregon, is dominated by spring snow melt which provides a natural large-amplitude 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 runoff-dominated streams at high elevations. We interpolate the time series of number of earthquakes, N, seismic moment, Mo, and stream discharge, Q, and determine cross-correlation coefficients at equivalent frequency bands between Q and both N and Mo. 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 κ~10-1 m2/s, a hydraulic conductivity of about Kh~10-7 m/s, and a permeability of about k~10-15 m2. Periodic boundary conditions also allow us to determine a critical pore-fluid pressure fraction, P'/P0~0.1, of the applied near-surface pore-fluid pressure perturbation, P0~0.1 MPa, that has to be reached at the mean earthquake depth to cause hydroseismicity. The low magnitude of P'~0.01 MPa is consistent with other studies that propose 0.01<=P'<=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.

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