HR: 0800h
AN: S41B-1002    [Abstracts]
TI: A Laboratory Investigation of Off-Fault Damage: Effects on Rupture Velocity
AU: * Biegel, R L
EM: biegel@usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089-0740 United States
AU: Sammis, C G
EM: sammis@usc.edu
AF: University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089-0740 United States
AU: Rosakis, A J
EM: rosakis@aero.caltech.edu
AF: California Institute of Technology, 1200 East California Boulevard , Pasadena, CA 91125 United States
AB: Rice et al. (2005) formulated an analytical model for dynamic propagation of a slip-pulse on a fault plane. Using earthquake parameters analyzed by Heaton (1990), they found that stress concentration at the rupture front should produce granulation of fault rock to a distance of a few meters and wall rock fracture damage to 10s of meters. This off-fault damage contributes to the fracture energy and therefore affects rupture velocity; an effect not addressed by Rice et al. Our challenge is to quantify this feedback for incorporation into the slip-pulse model. To this end we conducted 35 experiments using photoactive homalite samples (Xie et al., 2004). We measured rupture velocities in samples having off-fault "damage elements" introduced in the form of small slits of different lengths that intersected the fault plane over a range of angles. Most experiments with damage elements 1.0 cm and 0.5 cm in length and oriented 45 degrees to the fault plane temporarily decreased the rupture velocity in the area of the element but did not nucleate new damage. We attribute the transient velocity change to a reduction of the stress intensity factor, K-II, due to blunting of the rupture tip by the damage elements. In these cases the rupture velocity was restored and temporarily augmented for a short distance beyond the damage element until the rupture displacement matched that expected for linear propagation in the absence of the damage element. In a few experiments with shorter slits (0.5 cm and 0.25 cm) oriented 45 degrees to 70 degrees to the fault plane, the damage element nucleated additional damage in the form of a mode-I tensile wing-tip crack. As the rupture approached the damage element a velocity reduction occurred followed by a velocity rebound, but these experiments produced a permanent delay in the displacement-time curves. We attribute this offset to energy dissipation due to frictional sliding and increased fracture energy necessary to create fresh crack surface.
DE: 7209 Earthquake dynamics (1242)
DE: 8010 Fractures and faults
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Seismology [S]
MN: Fall Meeting 2005