HR: 09:00h
AN: NG31A-05 INVITED     [Abstracts]
TI: Modeling of regional earthquakes, aseismic deformation and fault patterns
AU: * Lyakhovsky, V
EM: vladi@geos.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhei Israel str., Jerusalem, 95501 Israel
AU: Ben-Zion, Y
EM: benzion@usc.edu
AF: Earth Sciences Dept., University of Southern California, Los Angeles, CA 90089-0740 United States
AB: We study the coupled evolution of earthquakes and faults in a 3-D lithospheric model consisting of a weak sedimentary layer over a crystalline crust and upper mantle. The total strain tensor in each layer is the sum of (1) elastic strain, (2) damage-related inelastic strain, and (3) ductile strain. We use a visco-elastic damage rheology model (Lyakhovsky et al., 1997; Hamiel et al., 2004) to calculate elastic strain coupled with evolving material damage and damage-related inelastic strain accumulation. A thermodynamically based equation for damage evolution accounts for degradation and healing as a function of the elastic strain tensor and material properties (rate coefficients and ratio of strain invariants separating states of degradation and healing). Analyses of stress-strain, acoustic emission and frictional data provide constraints on the damage model parameters. The ductile strain in the sedimentary layer is governed by Newtonian viscosity, while power-law rheology is used for the ductile strain in the lower crust and upper mantle. Each mechanism of strain and damage evolution is associated with its own timescale. In our previous study of earthquakes and faults in a 2-D model with averaged stress distribution over the seismogenic zone (thin sheet approximation) we demonstrated effects associated with the ratio between time scales for damage healing and for tectonic loading. The results indicated that low ratio leads to the development of geometrically regular fault systems and the characteristic frequency-size earthquake statistics, while high ratio leads to the development of a network of disordered fault systems and the Gutenberg-Richter statistics. Stress relaxation through ductile creep and damage-related strain mechanisms is associated with two additional time scales. In contrast to the previous 2-D model, the thickness of the seismogenic zone is not prescribed by the model set-up, but is a function of the ratio between timescale of damage accumulation and depth-dependent timescale of ductile stress relaxation. Thus, high strain rates generated by large earthquakes (mainshocks) lead to transient deepening of the brittle-ductile transition and gradual decrease of the maximum hypocenter depth with time from the mainshock. The ratio between the time scale of damage accumulation and time scale of damage-related irreversible strain controls the partition of the stored strain energy in the seismogenic zone between seismic and aseismic components of deformation. Analytical and numerical results show that properties of aftershock sequences are very sensitive to this ratio. Comparison between 3-D modeling and seismic activity in the Dead Sea region indicates that the degree of seismic coupling is very low in the central and northern parts of the Dead Sea Transform, in agreement with previous independent estimates.
DE: 3225 Numerical approximations and analysis (4260)
DE: 4255 Numerical modeling (0545, 0560)
DE: 7209 Earthquake dynamics (1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005