Near-Field Particle Velocity Signatures of Supershear Ruptures: Theory and Experiments
Michael Mello (Georgia Institute of Technolog), Ares Rosakis (California Institute of Technology)
Symposium in honor of Rod Clifton on the occasion of his 75th Birthday
Mon 10:45 - 12:15
Salomon 101
We have recently examined and validated several theoretically predicted, near-field signatures of supershear ruptures using a modified version of the laboratory earthquake setup originally developed by Rosakis and co-workers (Xia et al., 2004, 2005). Heterodyne laser interferometers are used to obtain continuous particle velocity records at discrete stations on the surface of a Homalite-100 test specimen as a supershear or sub-Rayleigh rupture propagates along the frictional fault. A photoelastic image sequence is simultaneously acquired using high-speed digital photography in order to obtain a synchronized and spatially resolved, whole field view of the event. Ground motion attenuation of sub-Rayleigh and supershear rupture fields is considered by examining particle velocity jumps measured at various off-fault positions and comparing these values to the corresponding on-fault velocity jump triggered by the passage of the rupture. Experimental findings confirm the dominance of the fault parallel motion component in the stable rupture speed regime and also reveal how radiated energy is portioned between the shear and dilatational fields. The latter feature is uniquely attributed to supershear ruptures and has no direct counterpart in the sub-Rayleigh rupture speed regime. Several additional unique and defining signatures of supershear ruptures are demonstrated by our laboratory experiments and rationalized by appealing to the 2D elastodynamic theory.