HR: 09:00h
AN: S51F-04    [Abstracts]
TI: Rupture Paths in Kappa-Maps: Quantitative Insights on Heterogeneous Earthquake Ruptures From Energy Arguments.
AU: * Ampuero, J
EM: ampuero@erdw.ethz.ch
AF: Institute of Geophysics ETH Zurich, ETH Hönggerberg (HPP), Zürich, CH-8093 Switzerland
AU: Ripperger, J
EM: ripperger@sed.ethz.ch
AF: Institute of Geophysics ETH Zurich, ETH Hönggerberg (HPP), Zürich, CH-8093 Switzerland
AU: Mai, M
EM: martin.mai@sed.ethz.ch
AF: Institute of Geophysics ETH Zurich, ETH Hönggerberg (HPP), Zürich, CH-8093 Switzerland
AB: Earthquake rupture is a notoriously complex process, at all observable scales. Although heterogeneities of strength and initial stress contribute to this rupture complexity, a systematic approach to quantify their effect has not yet been attempted. For instance, little is known about the relation between the final size of an earthquake and the statistical properties of initial strength excess fields. Canonical cases of dynamic rupture (e.g. uniform initial stress and friction properties), can be characterized by two non-dimensional numbers: the S-parameter (ratio of strength excess to stress drop) and the Kappa-parameter (ratio of static energy release rate to fracture energy, Madariaga and Olsen, 2000). The latter was introduced as a global parameter, involving the fault depth or asperity size as the fundamental scale. However, because faults contain heterogeneities at all scales it is not clear how a single scale-length may be relevant to define Kappa. We define here a scale-dependent Kappa-map, based on classical energy concepts in fracture mechanics. In 2D these maps can be defined exactly, and their efficient computation is implemented as a series of FFT-convolutions, by scaled analytical filters related to stress intensity factor weight functions. For given heterogeneous stress drop and fracture energy, such Kappa-maps are useful to predict nucleation properties and final moment, as we illustrate through increasingly complex examples complemented by dynamic rupture simulations. Other properties that can be derived from the 2D Kappa-maps, with additional assumptions, include radiated energy and rupture directivity. In 3D, the shape of the rupture front is unknown a priori and the energy release rate G might be non-uniform along the front. We therefore propose an approximate definition of Kappa in which G is estimated on circular patches. Comparisons with 3D dynamic rupture simulations on highly heterogeneous initial stress fields show that the final moment can be estimated with the Kappa map when the circular assumption is not strongly violated. We show how the problem of two-patch interaction can be handled by consistent methods, while more complex cases (rupture front fingering, interaction and coalescence between asperities, non connected rupture fronts) require more sophisticated considerations beyond our deliberately simple initial approach. This study combined with constraints from strong motion seismology and statistical descriptions of seismicity is a building block towards a physically-based parametrization of kinematic rupture models for ground-motion simulations.
DE: 7209 Earthquake dynamics (1242)
DE: 7260 Theory
DE: 7290 Computational seismology
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: Fall Meeting 2005