Deformation of compliant fault zones induced by nearby earthquakes: Theoretical investigations in two dimensions
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Using spontaneous rupture models with off-fault elastoplastic material response, we investigate the deformation of compliant fault zones induced by nearby earthquake ruptures in a two-dimensional plane-strain framework. We find that dynamic stresses from nearby ruptures can produce inelastic strain along some portions of a fault zone that experience dilatational stress changes, if the fault zone rock is close to failure in the prestress field. Accumulation of inelastic strain causes dramatic variations in particle velocity across the fault zone, reversing the sense of fault-parallel relative motion from retrograde (opposite to the long-term geologic slip) to sympathetic (consistent with the long-term slip) during the dynamic process. In the static displacement field of a roughly parallel strike-slip fault system, the inelastic response of a fault zone results in sympathetic motion, while the elastic response generally gives rise to retrograde motion. Our theoretical investigations reveal that some deficiencies may exist in applying an elastic inhomogeneity model to infer fault zone properties in previous studies, including the assumption of negligible fault-normal motion and ignorance of changes in some components of the stress tensor. These deficiencies and possible constraints on the in situ stress state by inelastic strain signals in the static displacement field call for a reexamination of existing observations of fault zone deformation induced by recent large earthquakes. Copyright 2011 by the American Geophysical Union.
