Abstract

We present an experimental and numerical investigation of the interaction of a Rayleigh (R) pulse with a partially contacting strike-slip fault between similar and dissimilar materials. This study is intended to offer an improved understanding of the earthquake rupture mechanisms. The fault is subjected to static normal and shear prestresses. Utilizing two-dimensional dynamic photoelasticity in conjunction with high-speed cinematography, the evolution of time-dependent isochromatic fringe patterns (contours of maximum in-plane shear stress) associated with Rayleigh pulse-fault interaction is experimentally recorded. It is shown that fault slip (instability) can be triggered by a pulse that propagates along the fault interface at Rayleigh wave speed (about 90% of the relevant shear wave speed) and that the direction of the static shear preloading has an influence on the initiation of fault slip. For the numerical studies, a finite-difference wave propagation simulator SWIFD (solids wave impact fracture damage) is used for a quantitative analysis of the problem under different combinations of contacting materials. Dynamic rupture in laterally heterogeneous structures is discussed by considering the effect of the acoustic impedance ratio of the two contacting materials on the wave patterns. The results indicate that upon fault rupture, Mach (head) waves, which carry a relatively large amount of concentrated energy, can be generated that propagate from the fault contact region into the acoustically softer material. Such Mach waves can cause concentrated damage in a particular region located inside an adjacent acoustically softer area. This type of damage concentration might be another possible reason for the generation of the damage belt in Kobe, Japan, on the occasion of the 1995 Hyogo-ken Nanbu earthquake.

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