The Effect of Asymmetric Damage on Dynamic Shear Rupture Propagation II: With Mismatch in Bulk Elasticity

Harsha S. Bhat, Ronald L. Biegel, Ares J. Rosakis, & Charles G. Sammis

Published 2010, SCEC Contribution #1236

We investigate asymmetric rupture propagation on an interface that combines a bulk elastic mismatch with a contrast in off-fault damage. Mode II ruptures propagating on the interface between thermally shocked (damaged) Homalite and polycarbonate plates were studied using high-speed photographs of the photoelastic fringes. The anelastic asymmetry introduced by damage is defined by `T' and `C' directions depending on whether the tensile or compressive lobe of the rupture tip stress concentration lies on the damaged side of the fault. The elastic asymmetry is commonly defined by `+' and `-' directions where `+' is the direction of slip of the more compliant material. Since damaged Homalite is stiffer than polycarbonate, the propagation directions in our experiments were `T+' and `C-'. Theoretical and numerical studies predict that a shear rupture on an elastic bimaterial interfaces propagates in the `+' direction at the generalized Rayleigh wave speed or in some numerical cases at the P-wave speed of the stiffer material, {fast}$. We present the first experimental evidence for propagation at {fast}$ in the `+' direction for the bimaterial system undamaged Homalite in contact with polycarbonate. In the `-' direction, both theory and experiments find ruptures in elastic bimaterials propagate either at sub-shear speed or at the P-wave speed of the softer material, {slow}$, depending on the loading conditions. We observe that the off-fault damage effect dominates the elastic bimaterial effect in dynamic rupture propagation. In the `C-' direction the rupture propagates at sub-shear to supershear speeds, as in undamaged bimaterial systems, reaching a maximum speed of {slow}$. In the `T+' direction however the rupture propagates at sub-shear speeds or comes to a complete stop due to increased damaged activation (slip and opening along micro-cracks) which results in a reduction in stored elastic potential energy and energy dissipation. Biegel et al. [2008b] found similar results for propagation on the interface between Homalite and damaged Homalite where rupture speeds were slowed or even stopped in the `T-' direction but were almost unaffected in the `C+' direction.

Bhat, H. S., Biegel, R. L., Rosakis, A. J., & Sammis, C. G. (2010). The Effect of Asymmetric Damage on Dynamic Shear Rupture Propagation II: With Mismatch in Bulk Elasticity. Tectonophysics,. doi: 10.1016/j.tecto.2010.03.016.