HR: 11:35h
AN: S32B-06    [Abstracts]
TI: Identifying Self-healing Pulses and Crack-like Ruptures in Experiments
AU: * Rosakis, A J
EM: rosakis@aero.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd, MS 105-50, Pasadena, CA 91125 United States
AU: Lykotrafitis, G
EM: gcl@its.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd, MS 105-50, Pasadena, CA 91125 United States
AB: Theoretical and numerical models predict that dynamic shear ruptures generated during earth faulting can occur either as cracks or as self-healing slip pulses depending on the friction law, the boundary conditions and the geometry used in the modeling. An experimental investigation was conducted to study dynamic rupture at high rates along an incoherent (frictional) interface between two identical Homalite plates subjected to impact shear loading. The plates were held together by external pressure and one plate underwent to an edge impact near the interface. The dynamic stress field developed during the event was recorded in real time by high-speed photography used in conjunction with classical dynamic photoelasticity. In addition to high-speed photography, a recently introduced velocimetry technique based on laser interferometry was employed to record the slip rate history during sliding. The simultaneous use of the above techniques provided direct physical evidences of the rupture mode type, the exact point of rupture initiation, the sliding velocity history at a point on the interface and the rupture propagation speed. For the first time thus, we were able to conclusively identify a crack-like rupture, a self-healing slip pulse and a mixed mode of rupture in the form of sliding pulses followed by a crack. Unlike classical shear cracks in coherent interfaces of intrinsic strength and toughness, sliding areas in frictional (incoherent) interfaces seems to grow without noticeable acceleration phases and at various discreet speeds. A relatively broad head wave that emanated from the interface was observed. It was caused by the interaction between the impact wave and the preexisting static stress field. There was a cusp in the stress contours at the interface, indicating that the propagation speed was slightly faster along the interface than in the bulk. The propagation speed of the rupture tip spans the whole speed interval from sub-Rayleigh speeds to almost sonic speeds, with the exception of a narrow area between the Rayleigh wave speed and the Shear wave speed of Homalite. Supersonic trailing pulses were also observed. When the rupture speeds were supershear, Mach lines with different inclination and emanating from the rupture zone tips were discovered. Self-sustained fringe patterns propagating along the interface were identified as sliding pulses traveling ahead of the rupture tip of crack-like rupture. Behind the rupture point, robust fringe structures traveling at a constant speed (between the Rayleigh wave speed and the shear wave speed of Homalite) were detected. The above fringe structures correspond to wrinkle-like pulses propagating along the interface. In summary, the experiments provided conclusive evidence of the occurrence of various sliding rupture modes (crack-like, pulse-like or mixed) propagating dynamically along incoherent interfaces. Of particular interest here is the first experimental evidence of the formation of sliding pulses of the self-healing type leading the first direct validation of predictions made on the basis of theoretical and numerical models of dynamic shear rupture. Finally, the experiments provided hints of the dominant physical mechanisms governing the choice of various rupture modes and their evolution.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7209 Earthquake dynamics (1242)
SC: Seismology [S]
MN: Fall Meeting 2005