HR: 13:40h
AN: S13D-01    [Abstracts]
TI: Fault strength loss, slip velocity, and near-fault particle velocity during dynamic rupture propagation.
AU: * Beeler, N M
EM: nbeeler@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AU: Kilgore, B
EM: bkilgore@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AU: Boettcher, M
EM: mboettcher@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AU: McGarr, A
EM: mcgarr@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AU: Fletcher, J B
EM: jfletcher@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AU: Baker, S
EM: srbaker@nps.edu
AF: Naval Postgraduate School, Dept. of Physics, Code PH/Ba, 833 Dyer Road, Monterey, CA 93943,
AU: Evans, J
EM: jrevans@usgs.gov
AF: USGS, 345 Middlefield Rd MS 977, Menlo Park, CA 97025,
AB: Near-fault particle velocity depends on the total energy released minus the portion of this energy that is dissipated and stored within the earthquake source. In earthquake source models without rupture propagation and where shear strength loss is instantaneous, the peak particle velocity is proportional to the shear strength loss (effective stress) and the wave speed [e.g., Brune, 1970]. In models incorporating dynamic rupture propagation, the propagation speed of the rupture front, rather than the wave speed, and changes in stress components other than shear stress, determine the peak particle velocity. To test these models from theoretical seismology, and to establish empirical relations amongst fault slip rate, off- fault particle velocity, fault strength loss and stress state, laboratory measurements were made during dynamic rupture propagation on a 2 m x 0.4 m fault surface between granite blocks. At multiple locations along strike and at small distances normal to strike, shear stress, particle velocity and acceleration were recorded at a sampling rate of 1 MHz. Fault slip was also recorded at multiple locations along strike. In these experiments the fault strength loss is not abrupt, because of significant on-fault fracture energy. As a consequence, in the early stages the rupture front accelerates slowly. Despite these complications, preliminary results show clear proportionality between the spatially averaged stress drop and local peak or average slip rates. The relations between local stress drop, local slip rate, rupture propagation speed and off-fault particle velocity are, as yet, not entirely clear. Instrumentation is currently being added to record changes in the tensor stress components to characterize the complete local stress state at multiple locations during propagation and arrest. We anticipate that analysis of this more comprehensive data set will clarify the relationships between the various rupture parameters.
DE: 7209 Earthquake dynamics (1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Seismology [S]
MN: 2007 Fall Meeting