Creep modulation of Omori law generated by a Coulomb stress perturbation in a 3-D rate-and-state asperity model
Résumé
We present numerical simulations conducted with a quasi-dynamic, 3-D
rate-and-state asperity model and an analytical approach in order to study the behavior of
a seismic asperity surrounded by aseismic creep in response to external Coulomb stress
perturbations. This work is inspired by the observation of Omori decay characterizing the
recurrence time of isolated repeating earthquakes, such as at the Parkfield segment of the
San Andreas Fault during the postseismic phase of the 2004 Mw 6 event. Based on the
numerical results and on an analysis of phase diagrams, we identify two possible regimes
that characterize the response of an asperity surrounded by aseismic creep to a stress step,
depending on an effective steady state friction parameter A. For the specific perturbation
used in this study, we observe that when A is positive, the relaxation of the system is
governed by the response of the creeping segments of the fault, and the asperity ruptures
in an Omori sequence. In this regime, we demonstrate that the duration of the relaxation
process depends on A. Furthermore, we show that this effective strengthening behavior is
equivalent to a subcritical density of asperities meaning that the shape of the Omori decay
is controlled by the relative proportion of seismic and aseismic material within the fault.
On the other hand, a fault characterized by effective steady state weakening (A<0)
behaves like a spring and slider system that loses the memory of the stress perturbation
once the first aftershock occurred, at least in the simulations presented here.
Domaines
Géophysique [physics.geo-ph]Origine | Fichiers éditeurs autorisés sur une archive ouverte |
---|
Loading...