HR: 11:05h
AN: S41G-03    [PDF]
TI: Earthquake Apparent Stress Scaling for the 1999 Hector Mine Sequence
AU: * Walter, W R
EM: bwalter@llnl.gov
AF: Earth Sciences Division, Lawrence Livermore National Lab. L-205, P.O. Box 808, Livermore, CA 94551
AU: Mayeda, K
EM: kmayeda@llnl.gov
AF: Earth Sciences Division, Lawrence Livermore National Lab. L-205, P.O. Box 808, Livermore, CA 94551
AB: There is currently a disagreement within the geophysical community on the way earthquake energy scales with magnitude. One set of studies finds evidence that energy release per seismic moment (apparent stress) is constant (e.g. Choy and Boatwright, 1995; McGarr, 1999; Ide and Beroza, 2001). Other studies find the apparent stress increases with magnitude (e.g. Kanamori et al., 1993; Abercrombie, 1995; Mayeda and Walter, 1996; Izutani and Kanamori, 2001). The resolution of this issue is complicated by the difficulty of accurately accounting for attenuation, radiation inhomogeneities, bandwidth and determining the seismic energy radiated by earthquakes over a wide range of event sizes in a consistent manner. We try to improve upon earlier results by using consistent techniques over common paths for a wide range of sizes and seismic phases. We have examined about 130 earthquakes from the Hector Mine earthquake sequence in Southern California. These earthquakes range in size from the October 16,1999 Mw=7.1 mainshock down to ML=3.0 aftershocks into 2000. The mainshock has unclipped Pg and Lg phases at a number of high quality regional stations (e.g. CMB, ELK, TUC) where we can use the common path to examine apparent stress scaling relations directly. We are careful to avoid any event selection bias that would be related to apparent stress values. We fix each stations path correction using the independent moment and energy estimates for the mainshock. We then use those corrections to determine the seismic energy for each event based on regional Lg spectra. We use a modeling technique (MDAC) based on a modified Brune (1970) spectral shape but without any assumptions of corner-frequency scaling (Walter and Taylor, 2002). We perform similar analysis using the Pg spectra. We find the energy estimates for the same events are consistent for Lg estimates, Pg estimates and the estimates using the independent regional coda envelope technique (Mayeda and Walter, 1996; Mayeda et al, 2003). So far the results show the seismic energy to moment values or apparent stress increases with moment similar to our 1996 study. We plan to perform similar studies for other Southern California earthquake sequences. 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.
UR: http://earthscience.llnl.gov/scaling-workshop/
DE: 7203 Body wave propagation
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting