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| Titel |
Regularization of rupture dynamics along bi-material interfaces: a parametric study and simulations of the Tohoku earthquake |
| VerfasserIn |
Antonio Scala, Gaetano Festa, Jean-Pierre Vilotte |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105295
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| Publikation (Nr.) |
 EGU/EGU2015-4794.pdf |
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| Zusammenfassung |
| Faults are often interfaces between materials with different elastic properties. This is
generally the case of plate boundaries in subduction zones, where the ruptures extend for
many kilometers crossing materials with strong impedance contrasts (oceanic crust,
continental crust, mantle wedge, accretionary prism). From a physical point of view, several
peculiar features emerged both from analogic experiments and numerical simulations for a
rupture propagating along a bimaterial interface. The elastodynamic flux at the rupture tip
breaks its symmetry, inducing normal stress changes and an asymmetric propagation. This
latter was widely shown for rupture velocity and slip rate (e.g. Xia et al, 2005) and was
supposed to generate an asymmetric distribution of the aftershocks (Rubin and Ampuero,
2007).
The bimaterial problem coupled with a Coulomb friction law is ill-posed for a wide range
of impedance contrasts, due to a missing length scale in the instantaneous response to the
normal traction changes. The ill-posedness also results into simulations no longer
independent of the grid size. A regularization can be introduced by delaying the tangential
traction from the normal traction as suggested by Cochard and Rice (2000) and Ranjith and
Rice (2000)
/Ïăeff α|v|+-v*
/t = δÏă (Ïăn - Ïăeff)
where Ïăeff represents the effective normal stress to be used in the Coulomb friction. This
regularization introduces two delays depending on the slip rate and on a fixed time
scale.
In this study we performed a large number of 2D numerical simulations of in plane
rupture with the spectral element method dynamic and we systematically investigated the
effect of parameter selection on the rupture propagation, dissipation and radiation, by also
performing a direct comparison with solutions provided by numerical and experimental
results.
We found that a purely time-dependent regularization requires a fine tuning rapidly
jumping from a too fast, ineffective delay to a slow, invasive, regularization as a function of
the actual slip rate. Conversely, the choice of a fixed relaxation length, smaller than the
critical slip weakening distance, provides a reliable class of solutions for a wide range of
elastic and frictional parameters. Nevertheless critical rupture stages, such as the
nucleation or the very fast steady-state propagation may show resolution problems
and may take advantage of adaptive schemes, with a space/time variation of the
parameters.
We used recipes for bimaterial regularization to perform along-dip dynamic simulations
of the Tohoku earthquake in the framework of a slip weakening model, with a realistic
description of the geometry of the interface and the geological structure. We finely
investigated the role of the impedance contrasts on the evolution of the rupture and short
wavelength radiation. We also show that pathological effects may arise from a bad selection
of regularization parameters. |
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