3D dynamic simulations of spontaneous rupture propagation governed by different constitutive laws with rake rotation allowed

A. Bizzarri, M. Cocco


In this work we present a 3D Finite Difference numerical method to model the dynamic spontaneous propagation
of an earthquake rupture on planar faults in an elastic half-space. We implement the Traction-at-Split-Nodes
fault boundary condition for a system of faults, either vertical or oblique, using different constitutive laws. We
can adopt both a slip-weakening law to prescribe the traction evolution within the breakdown zone or rate- and
state-dependent friction laws, which involve the choice of an evolution relation for the state variable. Our numerical
procedure allows the use of oblique and heterogeneous distribution of initial stress and allows the rake
rotation. This implies that the two components of slip velocity and total dynamic traction are coupled together
to satisfy, in norm, the adopted constitutive law. The simulations presented in this study show that the rupture
acceleration to super-shear crack speeds occurs along the direction of the imposed initial stress; the rupture front
velocity along the perpendicular direction is slower than that along the pre-stress direction. Depending on the
position on the fault plane the orientation of instantaneous total dynamic traction can change with time with respect
to the imposed initial stress direction. These temporal rake rotations depend on the amplitude of initial
stress and on its distribution on the fault plane. They also depend on the curvature and direction of the rupture
front with respect to the imposed initial stress direction: this explains why rake rotations are mostly located near
the rupture front and within the cohesive zone.


earthquake dynamics;numerical modeling;friction laws;slip time history;rake rotation

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DOI: https://doi.org/10.4401/ag-3201
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X