HR: 17:00h
AN: S12G-05    [PDF]
TI: Energy Scaling for the Hector Mine and Landers Sequences Using Coda-Derived Source Spectra
AU: * Mayeda, K M
EM: kmayeda@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, L-205, Livermore, CA 94551 United States
AU: Walter, W R
EM: walter@kaboom.llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, L-205, Livermore, CA 94551 United States
AB: Unlike the well-established techniques of long-period waveform modeling for seismic moment (Mo), the measurement of radiated seismic energy (E) requires corrections at and beyond the corner frequency of the event. At these shorter length scales the Earth is considerably more complicated making path and site response corrections the two most important considerations. To minimize the problem of determining path corrections, we have chosen the 1992 Landers and the 1999 Hector Mine sequences in southern California for study using broadband recordings from both local and regional broadband stations. To minimize the effect of source heterogeneity (e.g., directivity and source radiation pattern effects) we have used the coda methodology of Mayeda et al. (2003) to obtain stable, broadband source spectra which are a factor of 3-to-4 more stable than those derived from the direct waves. This methodology also uses small empirical Green's function events to derive site corrections to account for near-site attenuation and amplification. We independently validate our source spectra by comparing against network averaged moment estimates using long-period waveform modeling. Results for events ranging between Mw ~3 to 7+ for both sequences using the same methodology and stations clearly shows the scaled energy, e=E/Mo, increases with increasing magnitude. This departure from constant energy scaling had been observed elsewhere but has been questioned because of the large uncertainties in the path, site, and source heterogeneity corrections. We believe that this current study clearly points to a difference in rupture dynamics between small and large events in this sequence. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2003 Fall Meeting