Dehydration-Induced Porosity Waves and Episodic Tremor and Slip

Robert Skarbek, & Alan W. Rempel

Published August 10, 2016, SCEC Contribution #6611, 2016 SCEC Annual Meeting Poster #071

Episodic tremor and slip (ETS) at plate interfaces takes place where there is abundant evidence for elevated, near-lithostatic pore pressures. In subduction zones and on the San Andreas fault, tectonic tremor occurs at depths where there is evidence for a mixture of viscous and elastic deformation along the plate interface. Particularly in subduction zones, ETS occurs at sufficiently great depths where chemical dehydration reactions must act as the dominant fluid source. Here, we simulate fluid and heat flow while tracking the location of a vertically oriented, one-dimensional column of material as it subducts through the slow slip and tremor zone. The material in the column is transformed through a pressure-dependent and temperature-dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law. Column deformation is largely dominated by viscous creep, with a closure rate that depends linearly on porosity. This behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region. To explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves, we derive a dispersion relation that accurately describes our numerical results. We also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law. Although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings (e.g., tides or passing surface waves), our analysis suggests that given reasonable estimates of rock viscosity, permeabilities in the range 6.5x10-15 to 5x10-10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor.

Citation
Skarbek, R., & Rempel, A. W. (2016, 08). Dehydration-Induced Porosity Waves and Episodic Tremor and Slip. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)