HR: 17:45h
AN: S34A-08    [Abstracts]
TI: On the Partitioning of Mechanical Work Between Surface Energy and Heat During Earthquake Ruptures
AU: * Spudich, P
EM: spudich@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Cocco, M
EM: cocco@ingv.it
AF: Ist. Nazionale dI Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Tinti, E
EM: tinti@ingv.it
AF: Ist. Nazionale dI Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AB: The earthquake energy budget is usually formulated by the partitioning of elastic strain energy into radiated energy, frictional work and the fracture energy consumed as a rupture area expands. In the classical slip-weakening model, the dividing line between frictional work and fracture energy is assumed to be the constant sliding or residual stress value, and it is assumed that all the frictional work goes into heat. We present evidence from recent earthquakes that this assumed division between heat and fracture energy is not true of large earthquakes. We have inferred the traction evolution on a fault plane for several recent earthquakes and we have used the traction versus slip curves to measure the breakdown work at each point of the fault, defined as the excess of work over the minimum level of stress reached during slip at each point. Our definition of breakdown work is equivalent to fracture energy defined as above in the classic slip weakening model, but is applicable to complicated, empirically determined traction-slip curves with dynamic fault weakening and restrengthening. Breakdown work has a different physical interpretation than fracture energy as defined above in the slip-weakening model: although it is the work spent to allow the rupture to advance, geological estimates of surface energy suggest that for real earthquakes on natural fault zones breakdown work contains a mixture of heat and surface energy. This implies that the boundary between heat and surface energy probably does not lie along a horizontal line at the minimum level of residual stress. Our breakdown work estimates computed for extended earthquake models tend to be significantly larger than geological estimates of surface energy from the Punchbowl fault [Chester et al., 2005] and the San Andreas at Ft. Tejon [Wilson et al., 2005]. This suggests that breakdown work is expended both in heat and gouge formation/evolution during dynamic slip episodes, and that "seismological fracture energy" is not identical to the energy used to create fractures during earthquakes.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7260 Theory
SC: Seismology [S]
MN: Fall Meeting 2005