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| Titel |
Cycle and triggering of a rate-and-state asperity model. |
| VerfasserIn |
Pierre Dublanchet, Pascal Bernard, Pascal Favreau |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048816
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| Zusammenfassung |
| Some seismic sources can be seen as locked asperities on a fault surrounded by creeping
surfaces. We present here the results obtained by numerical modeling of such a system using
rate-and-state framework. In our approach, we consider two elastic semi-infinite half-spaces
in contact through an interface with heterogeneous friction properties. The elastic bodies are
forced to slip in opposite directions by maintaining a constant velocity at an infinite
distance above the fault plane. Asperities are modeled by patches with velocity
weakening properties, while creeping areas are modeled by velocity strengthening
behaviour.
To begin with, we analyse the response of a single circular asperity. In this case, regular
events with rapid unstable slip on the asperity, i.e. earthquakes, occur. These events are
separated by slow interseismic loading of the source. During all this sequence, we observe
stress interactions between velocity weakening and velocity strengthening parts of the
fault.
In addition, each seismic cycle on the asperity can be characterized by its duration, by the
stress drop on the source during instability, and the maximum displacement on the fault.
Consequently, we study the effect of friction parameters and geometrical parameters (in
particular ratio of weakening to strengthening area) on these properties of the seismic cycle
on the asperity. This analysis could enable us to interpret seismological observations in terms
of friction.
The behaviour of a single asperity is then compared to the case of a fault with uniform
weakening properties, which is an equivalent of a Burridge and Knopoff type model, and is in
fact the limit case of our model with a creeping area reduced to zero.
In a second time we perturbate the evolution of this system by introducing an instantaneous
uniform stress step which could represent the effect of a distant earthquake.
Such a stress change produces on a strengthening fault a slow transient with maximum
slipping velocity reached several hours or days after the perturbation, depending on the
amplitude of the stress step. The maximum velocity depends on the amplitude of the stress
perturbation as well.
In the case of a single asperity, this experiment is a way to study aftershocks that occur on
sources after a bigger earthquake or accompanying a large stress transient, each of these
sources being represented by an asperity surrounded by creeping areas. We consider a set of
identical asperities whose delays to rupture are uniformly distributed between 0 and T (T
being the recurrence time of the characteristic earthquake on one source). We are interested in
the timing of the events among this population of sources following a stress perturbation, and
we analyse the way earthquakes on these asperities are triggered by evaluating the delay
between stress perturbation and next rupture for each source. This distribution of delays is
interpreted in terms of Omori’s law and is compared to the analytic distribution
obtained by (Dieterich, 1994) for a set of springs and sliders. The distribution of delays
obtained is somewhat different from the one obtained for springs and sliders, owing to
complexe interaction between creeping parts and locked parts of the fault. A closer
match appears if the simulation is done with a set of uniform weakening faults, as
expected.
We used this model in the case of micro-seismicity but it may be applied to any larger size of
asperity able to generate big earthquakes. |
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