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Group 2 – FARM | Poster Abstracts
We show that some of the assumptions are questionable in the context of a model for 1D fault with
earthquake cycles controlled by rate-and-state-dependent friction. We compare results from the
two afterslip models with the postseismic phase of slip in the 1D rate-state friction models. We find
that effect of state evolution on the fault as the afterslip zone expands and propagates into the
velocity strengthening region is a significant factor in the rate of postseismic moment release on the
fault. Models that neglect state evolution during afterslip may lead to misestimates of friction
parameters using real data. We also find that assuming steady-state sliding before the earthquake
and imposing sudden coseismic slip leads to underestimates of the amount of postseismic slip
surrounding coseismic rupture because the initial sliding velocity is too low. Models assuming
velocity-strengthening friction may lead to underestimates of postseismic slip or overestimates of
the amount of coseismic slip needed to drive afterslip.
2-062
MACROSCOPIC DYNAMICS OF PULSE-LIKE RUPTURES IN SPATIALLY
HETEROGENEOUS STRESS FIELDS Elbanna AE, and Heaton TH
Earthquake ruptures are examples of multi-scale phenomena showing spatial and temporal
complexity. With the current computational capabilities, we are still far from running realistic 3D
numerical models that can simulate a number of earthquake cycles large enough to enable the
inference of reliable statistics and scaling laws. A big challenge then is to cross the computational
gap and try to find physically based reduced models that can replicate the macroscopic features of
that dynamical complexity.
As an attempt to achieve that goal, we studied the 1D spring-block-slider model. This model shows
many of the features of the real Earth, such as the Gutenberg-Richter scaling law and pulse-like
ruptures, besides having the merit of being computationally efficient. Moreover, we show here that
it also replicates some of the results obtained in full elasto-dynamic models (e.g. Shaw 2006) such
as average stress drop scaling. Our focus is on studying the dynamics of slip pulses in our model
and trying to deduce a dynamical system of equations that can describe sptatio-temporal evolution
of the slip pulses .
Our results show that the macroscopic dynamics of moderate and large events can be replicated by
studying the energy balance of the propagating pulse. By writing an evolution equation for the
kinetic energy of the pulse, we can predict when the pulse can grow or diminish. The kinetic
energy of the pulse is the difference between the available strain energy and the work dissipated in
friction. The higher the kinetic energy of the pulse the larger the pulse will be and vice-versa.
However, the energy balance equation is just one equation in more than one unknown; it connects
the kinetic energy to the pulse parameters (pulse width and amplitude) or the kinetic energy to the
final slip and the frictional work. Hence we have to complement it with empirical relations
between those parameters. We find a strong correlation between the pulse kinetic energy and the
pulse slip as well as the pulse slip and the frictional work. By substituting those findings back in
the energy balance equation, we can rewrite that equation either in terms of slip or kinetic energy.
By solving this equation we can produce the macroscopic features of isolated moderate and large
unilateral events (e.g. final slip, rupture length....etc).
Our future work aims at extending those results to small and bi-lateral events and examining
whether the repeated application of that equation would preserve the heterogeneity in the system
or not.
2008 SCEC Annual Meeting | 173