HR: 12:05h
AN: T42B-07 INVITED     [Abstracts]
TI: The Influence of Pore Pressure Variations in Fault Zones on Spatio-Temporal Seismicity Evolution
AU: * Hillers, G
EM: hillers@sed.ethz.ch
AF: ETH Zurich, Institute of Geophysics EHT Hoenggerberg HPP, Zurich, 8093 Switzerland
AU: Miller, S A
EM: steve.miller@sed.ethz.ch
AF: University of Bonn, Geodynamics/Applied Geophysics Nussallee 8, Bonn, 53115 Germany
AB: A consequence of a heterogeneous permeability structure within fault zones is pore pressure variations along fault planes. We study the influence of pore pressure variations by modeling the (continuum-limit) seismicity evolution of a 2D fault plane embedded in a 3D elastic solid, controlled by rate and state friction and an empirical law of porosity evolution. We systematically investigate the slip response of the fault as a function of fluid related parameters, such as the degree of overpressure, dilatancy and diffusivity. First, we explore the parameter space for homogeneous along-strike properties to investigate slip processes arising from purely physical mechanisms. Three types of responses emerge: (1) Unstable stick-slip behavior that typically evolves in all drained models and in undrained models if dilatant processes are sufficiently small. The functional dependence of system stiffness on hydraulic diffusivity and dilatancy is shown to correspond with interevent times of simulated stick-slip events. We show that evolution of fluid-related variables differ significantly between drained and undrained conditions. (2) Stable creep emerges in some conditions as a result of dilatant processes. (3) Systems situated in transitional regimes develop complex, nonuniform, nonstationary slip patterns in space and time, revealing a possible explanation for rupture termination and observed stable afterslip. Second, we investigate the effect of heterogeneous pore pressure regimes in a hydraulically isolated fault on spatio-temporal seismicity evolution. We apply different scales of heterogeneity and study the dependence of hypocenter locations on the degree of overpressurization. It is shown that earthquakes tend to nucleate in regions of relatively low pore pressure. This result is interpreted with a 1D stability analysis. The study demonstrates the important contribution of fluids in faults zones on the evolution of seismicity.
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 8010 Fractures and faults
DE: 8045 Role of fluids
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005