Analytical model for the activation of off-axis secondary faulting between two dissimilar rock layers

Abstract

Bimaterial faults can be found in nonhomogeneous rock media between dissimilar rock layers. An analytical model was extended for the right lateral strike-slip fault between two dissimilar rock layers to predict the activated tensile, right and left lateral shear zones around the fault tip. The effect of elastic modulus contrast (E2/E1, the ratio of the Young's moduli of the lower to the upper layer), rupture velocity (c), precompression stress ratio (-ϭxxo/-ϭyyo), residual to peak strength ratio (τr/rp) and fracture energy (G) were considered. Results show that under an intermediate rupture speed of (0.5 of the Rayleigh wave speed): the extension of activated tensile and shear zones depends strongly on the ratio of E2/E1 and it increases with increasing this ratio. The preferred direction of the new branches is little affected by the elastic modulus contrast. Increasing precompression stress ratio encourages right and left lateral shear branching on the compressional side of the fault and decreases the size of activated tensile and shear zones. Under an extreme rupture speed of (0.98 of the Rayleigh wave speed): the mechanism of branching differs, for E2/E1 < 1, the three activated zones are located in the lower layer and there is only a possibility for unilateral branching on the extensional side of the fault. For E2/E1 ≥ 1, right and left lateral shear zones extend to the upper layer (compressional side), which means the possibility of bilateral shear branching on the two sides of the fault. For all values of E2/E1, c, -ϭxxo/-ϭyyo, tensile branches can only be formed in the lower layer on the extensional side of the fault.