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Poster Abstracts | Group 2 – FARM
We also find that supershear transition in 3D models of long-term slip can be further promoted by
favorable compact fault heterogeneity, as suggested by the 2D single-event study of Liu and
Lapusta (2008). Our simulations show that adding a fault patch of lower effective peak frictional
resistance can qualitatively modify the behavior of the simulated fault, resulting in occasional
supershear earthquakes in a model that has no supershear events without the patch. Supershear
transition occurs at the location of the heterogeneity, as advocated by Liu and Lapusta (2008).
2-077
KINEMATIC INVERSION OF PHYSICALLY PLAUSIBLE EARTHQUAKE SOURCE
MODELS OBTAINED FROM DYNAMIC RUPTURE SIMULATIONS Konca AO, Kaneko
Y, Lapusta N, and Avouac J
A common approach to investigate earthquake physics consists of producing kinematic source
models from the inversion of seismic records jointly with geodetic data. The regularization of the
inversion requires some assumptions to restrict the range of possible models. Here, we evaluate to
what extent physically plausible models are reliably restituted in spite these restrictions. More
precisely we study which characteristics of ruptures, such as rupture velocity, slip distribution, and
rise time can be reliably determined from the inversion of near-field data. We use a standard
inversion scheme which assumes a rupture front propagating away from the hypocenter with a
simple cosine slip-time function, and searches for solutions with minimum roughness (Ji et al,
2002). To provide inversions with physically plausible sources, we generate several earthquake
scenarios using 3D spectral-element simulations of dynamic rupture (Kaneko et al., 2008). The
assumed model contains a planar fault in an elastic half-space. The fault is governed by rate and
state friction, with a velocity-weakening region surrounded by slip-inhibiting velocitystrengthening
regions. The fault properties are varied to obtain scenarios with different slip
distributions and local slip durations, leading to pulse and crack-like ruptures. For the inversion,
strike, dip, average rake, velocity model and the hypocenter are given, and we search for slip
evolution that best fits strong-motion and GPS data at simulated stations, without a priori
knowledge of moment, smoothness, rupture velocity, or slip distribution. The comparison with the
input model is done only after the best-fit model is chosen among various constraint inversions.
Our preliminary results show that, overall, rupture velocity and slip distribution are welldetermined.
Since we assume a single cosine for the slip-time function, both crack-like and pulselike
ruptures appear as pulses in the inverted models, but crack-like ruptures have larger spatial
extent at each moment. The difference between the two kinds of ruptures is thus still observable.
However, the slip history at a specific point on the fault cannot be obtained accurately due to the
assumed shape of the slip time function. This is probably the major drawback of these inversion
procedures. Our current work is therefore directed towards implementing different slip-time
functions to allow a wider range of possible behavior without adding complexity to the inversion.
2-078
INTERACTION BETWEEN DYNAMIC RUPTURE AND OFF-FAULT DAMAGE Xu S,
Ampuero J, Ben-Zion Y, and Lyakhovsky V
The high stress concentration at the front of a dynamic rupture is expected to produce rock damage
(reduction of elastic moduli) in the material surrounding the main fault plane. Off-fault yielding
and energy absorption in the damage process should reduce the amplitude of the ground motion.
However, the reduced elastic moduli in the damaged zone can amplify locally the motion and
create a waveguide that may allow the motion to propagate with little geometric attenuation. In
addition, the asymmetric damage generated in the in-plane rupture mode may produce bimaterial
interfaces that can reduce the frictional dissipation and increase the radiation efficiency.
182 | Southern California Earthquake Center