Scaling Off-Fault Damage from Field to Laboratory

Rice, Sammis and Parsons \(BSSA, 2004\) derived analytical expressions for a dynamical stress field in the vicinity of a propagating slip pulse on a fault plane. They found that the magnitude of off-fault stresses was primarily determined by the velocity of the propagating slip pulse and the normal and shear stresses applied to the fault. Coulomb failure on favorably oriented cracks was possible to a distance on the order of 1 to 2 times a scaling distance Ro*, the slip weakening distance in the limit of low velocity and infinite pulse length. Using parameters measured by Heaton \(1990\), Ro* for earthquakes, and hence the widths of the damage zones, were calculated to be 1 to 80 m. We scaled Ro* to laboratory dimensions by writing it as a function of Dc and strength drop. An experimental normal load of 10 Mpa and a characteristic displacement of 10 microns, yields Ro* of 14 cm. We also calculate a fracture energy of 42.9 J/m2 and locked in slip displacement of 12.9 microns. These values compare favorably with data from Abercrombie and Rice \(2004\), Heaton \(1990\) and Okubo and Dieterich \(1984\).