Spontaneous Rupturing Along a Frictional Interface

We designed a laboratory model to investigate the spontaneous rupturing along a frictionally held interface. A frictional contact, which mimics a material interface or geological fault, is simulated using two photoelastic plastics plates (Homalite or Polycarbonate) held together by friction and compression. The pre-uniaxial static loading is exerted by a hydraulic press. A unique design used in our experiments, which starts the spontaneous rupturing, is the exploding wire technique. It triggers the rupture within a controlled environment while keeping the spontaneous nature of the rupturing. The fault is oblique to the compression axis to provide the shear driving force for continued rupturing. We performed the spontaneous repturing experiment along an interface between both similar and dissimilar materials. Under proper loading conditions, a shear rupture which initially propagates at Rayleigh wave speed, jumps to a supershear speed (close to the longitudinal wave speed) after propagating a finite distance L in a similar material system. For the dissimilar material system, directionality of rupture propagation is observed. A rupture propagating at the generalized Rayleigh wave speed is observed in the same direction as the sliding of the more compliant material and in the opposite direction, supershear rupture is possible under proper loading condition.