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Group 2 – FARM | Poster Abstracts
Previous studies incorporated plastic yielding in simulations of dynamic rupture (Andrews, 1975,
2005; Ben-Zion and Shi, 2005; Templeton et al., 2008) while keeping the elastic moduli unchanged.
In this work we examine the dynamics of earthquake ruptures and generated motion in a model
consisting of a frictional fault in a medium governed by a continuum damage rheology for the
evolution of elastic moduli (e.g. Lyakhovsky and Ben-Zion, 2008). We perform numerical
simulations based on the Spectral Element Method to study how the parameters of the friction law,
damage rheology and background stress control the rate of growth of the off-fault damage zone,
the steady-state rupture speed, the energy balance, and the maximum slip rate and ground motion.
We find that, the maximum slip velocity, steady-state rupture speed and peak ground motion with
increasing values of the constitutive parameters Cd (the inverse of a damage timescale) and Cv (the
intensity of damage related plasticity). The relation between Cv, Cd and the rate of off-fault
damage growth with rupture distance is less trivial: the damage-induced bimaterial contrast grows
faster with increasing Cd, and the sign of the contrast changes at low Cv. We also compare peak
ground motion in our damage model to analogous simulations using Coulomb plastic yielding.
2-079
RUPTURE PROPAGATION AND SLIP PARTITIONING ON AN OBLIQUE UPWARD-
BRANCHING FAULT SYSTEM Oglesby DD, Bowman D, and Nunley ME
We use dynamic 3-D finite element analysis to investigate slip partitioning and rupture
propagation on an oblique left-lateral/normal fault system that branches near the surface into
vertical and non-vertical branches. The model consists of a 70° dipping oblique-slip fault that
extends from a depth of 15km to 5km depth and then branches upwards into a vertical segment
and a segment dipping 45° The use of a simple regional stress field resolved onto all fault segments
results in rupture propagation only on the base and vertical faults. However, the addition of a 2km
by 3km barrier onto the bottom portion of the vertical fault causes enough of a stress perturbation
on the upper dipping fault to nucleate rupture on this segment, resulting in a strongly partitioned
slip distribution in the system. In all cases, strike-slip motion is concentrated on the vertical fault,
and dip-slip motion is concentrated on the dipping fault. These results are not sensitive to the size
and along-strike location of the barrier. Other observations in our models show that as the dipping
fault slips, it induces a small amount of backwards slip on the vertical fault due to the high stress
drop in our models, and the close proximity of the two branch segments. Our results may have
important implications for the dynamics of branched faults and geometrically complex fault
systems in general.
2-080
LABORATORY INVESTIGATIONS OF THE ORIGIN OF PULVERIZED ROCKS Yuan
F, and Prakash V
Zones of pulverized rock have been observed in surface outcrops adjacent to the fault cores of the
San Andreas and other major faults in Southern California. These pulverized rocks consists of
highly fractured fragments that still fit together and essentially preserve the original rock texture.
The origin of these pulverized rocks is not clear, but their structural context indicates that they are
clearly associated with faulting; an understanding of their origin might allow inferences to be
drawn about the nature of dynamic slip on faults, including inferences concerning the coseismic
resistance to slip, energy balance of earthquakes, and implications for ground motions and
radiation patterns near faults. In the present study, a series of laboratory experiments are
conducted on Westerly granite rock samples to investigate whether pulverized rocks can be
produced under stress-wave loading conditions in the laboratory and whether they are diagnostic
of any particular process of formation. In the first series of experiments a Split Hopkinson pressure
2008 SCEC Annual Meeting | 183