Rupture directionality of dynamic rupture propagation at bimaterial interface in 3D

Dr. Luis A. Dalguer (ETHZ), Prof. Steven M. Day (SDSU, USA)

Normal stress perturbations accompany propagating mode II rupture along an interface separating materials of contrasting elastic compliance. We show, by numerical simulations in 3D (see figure below), that purely geometrical effects leading to pulse-like rupture, due to this normal stress perturbation, can induce strong asymmetries (and under very limited conditions can even evolve into strictly unilateral rupture), even when frictional rate dependence is neglected. The effect is studied here in a context that can only apply to strike-slip earthquakes large enough to rupture the entire seismogenic thickness, but the results suggest that other geometrical effects leading to pulse-like rupture will interact with a compliance contrast in a similar manner.

_{Figure: Rupture-time contours (0.5 sec intervals) for six fault models with fault length 120km. Models in a, b, c and d are embedded (no-freesurface); and models e and f are with free-surface. Figure g (bottom) is a top view of faul model, where preferred (positive) and non-prefered (negative) rupture directions are defined. Star indicates center of nucleation zone.}

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Dalguer, L. A. and Day, S. M. (2009), Asymmetric Rupture of Large Aspect-ratio Faults at Bimaterial Interface in 3D. Geophysical Research Letters (download)