HR: 1340h
AN: T53C-1447    [Abstracts]
TI: Fluid-driven Aftershocks and Omori's Law
AU: * Miller, S A
EM: miller@geo.uni-bonn.de
AF: Geodynamics, University Bonn, Nussallee 8, Bonn, 53115 Germany
AB: The spatio-temporal evolution of aftershock sequences from a variety of tectonic environments shows evidence that a high pressure fluid source at depth drives fluid through the crust and triggers aftershocks along the flow path. The positive feedback between fluid-pressure-driven faulting, and the subsequent large-scale change in permeability due to slip, allows the pressure pulse to travel at high rates. The coupling of large co-seismic permeability changes with an effective-stress-dependent permeability results in a highly non-linear diffusion process. Numerical modeling of this scenario shows that Omori's Law is easily reproduced. The Omori Law states that the rate of aftershocks decays as a power-law in time, and is found to hold for most aftershock sequences. The decay rate, described by the p-value, can vary between aftershock sequences, but the controls on the decay rate have not been explained. It is shown that the rate of aftershock decay is controlled by the regional stress field, with faster decay rates where the mainshock rupture is not optimally oriented, and slower decay rates where the mainshock rupture is aligned with optimally oriented planes. That is, for non-optimally oriented planes, the high effective normal stress restricts permeability and shuts down the permeable pathways. Conversely, the higher permeability of optimally oriented faults allows flow paths to remain open for longer periods of time to contribute to the aftershock sequence.
DE: 4445 Nonlinear differential equations
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
SC: Tectonophysics [T]
MN: Fall Meeting 2005