HR: 0800h
AN: S21B-0565    [Abstracts]
TI: Smooth, Mature Faults Radiate More Energy than Rough, Immature Faults in Parkfield, CA
AU: * Harrington, R M
EM: rebecca@moho.ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive East 3806 Geology Building, Los Angeles, CA 90095-1567, United States
AU: Brodsky, E E
EM: brodsky@es.ucsc.edu
AF: University of California, Santa Cruz, 1156 High St. Santa Cruz, CA 95060, Santa Cruz, CA 95060, United States
AB: Laser-based observations of fault surfaces indicate that cumulative slip is inversely related to fault roughness in the direction of slip, suggesting that older, more mature faults are smoother than younger ones with less cumulative slip (Sagy, et al., 2006). Given a difference in roughness between old and young fault surfaces, it is conceivable that earthquakes on older, smoother faults might radiate different amounts of seismic energy than earthquakes of comparable size on younger, rougher faults. The total energy budget of an earthquake is limited by the release of elastic strain energy associated with faulting. If more energy is required to rupture asperities on a rougher fault, a smaller portion of the total budget is available for the radiation of seismic waves. Radiated seismic energy is the only directly observable parameter in the partitioning of the earthquake energy budget, and the ratio of radiated energy to moment therefore provides information about rupture velocity. If fault roughness affects radiated energy, then such geological observations could also provide information about rupture propagation. We compare spectral shapes of earthquakes on old and young faults in the Parkfield area to observe if differences in roughness affect radiated energy. We use earthquakes of comparable magnitude below M_w 3.7, and assume that secondary faults have less cumulative displacement than the San Andreas Fault. The spectra of earthquakes on secondary faults have high-frequency bands depleted in amplitude relative to earthquakes on the San Andreas Fault. Additionally, the cumulative spectral energy based on these spectra give on average three times higher ratios of radiated energy to moment for the earthquakes on the San Andreas Fault. This suggests that mature, i.e. smoother faults are more efficient radiators of seismic energy.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7215 Earthquake source observations (1240)
DE: 7250 Transform faults
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting