Constraining The Near Tip Stresses Around Propagating Earthquake Ruptures: Frictional Response And Off Fault Tensile Crack Development

Abstract

The near-tip stress, strain, and displacement fields around propagating ruptures are complicated, transient, and depend heavily on the evolution of the shear traction along the advancing rupture. This shear traction evolution is in turn influenced by dynamic weakening of the coefficient of friction. I have investigated near tip rupture mechanics using two approaches. In the first approach, I conduct experiments using a novel torsional Kolsky bar apparatus to investigate the frictional evolution of synthetic rock gouges at pressures, accelerations, and slip velocities expected to be operating in the seismogenic zone where most earthquakes nucleate. Microstructural analysis and 1-D thermal modeling is conducted to explore the observed dynamic weakening of friction, and in particular the inferred mechanism of flash heating at asperity contacts. In the second approach, I examine length and spacing distributions of naturally occurring pseudotachylite injection veins and experimentally generated tensile microcracks to elucidate the mechanical interaction between mode I cracks within the transient near-tip stress field. As a rupture propagates, stress perturbations result in the formation of a tensile zone directly behind the rupture tip where fractures develop and fracture length is governed by stress shadowing of nearby fractures.