HR: 0830h
AN: S21E-0346    [PDF]
TI: Largest Expected Magnitudes During Finite Time Intervals on California Faults
AU: * Jackson, D D
EM: djackson@ucla.edu
AF: UCLA, Dept. Earth & Space Sciences 595 Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Liu, Z
EM: zliu@ess.ucla.edu
AF: UCLA, Dept. Earth & Space Sciences 595 Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Kagan, Y Y
EM: ykagan@ucla.edu
AF: UCLA, Dept. Earth & Space Sciences 595 Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Mualchin, L
EM: Lalliana_Mualchin@dot.ca.gov
AF: CALTRANS, 1120 N. Street, Sacramento, CA 95814 United States
AB: We estimate the largest magnitude expected with a given probability in a given time interval, for individual faults in California. We refer to such a quake as the "Functional Evaluation Earthquake, and to its magnitude as MFEE. For selecting scenario earthquakes in engineering studies, our approach provides an alternative to the "maximum credible earthquake" magnitude, MMCE [Mualchin et al., Caltrans Technical Report, 1996]. We assume a truncated Gutenberg-Richter magnitude distribution. We estimate the upper magnitude limit MMCE for each fault segment from the Wells and Coppersmith [1994] empirical relation between magnitude and fault length. We combined fault slip rates from the USGS/CDMG and the CALTRANS fault databases to estimate tectonic moment rate for each fault. We then assume a uniform b-value (1.0) and determine the a-value, which matches the tectonic moment rate for each fault. By definition, the estimated MFEE is lower than MMCE. It depends on the magnitude-frequency distribution, assumed probability level (P), considered time interval (T), and indirectly on the upper magnitude limit. The a-value decreases as the MMCE increases, and for some cases, this causes the MFEE to decrease as well. We summed the magnitude distributions for all faults to obtain a theoretical magnitude distribution for California. This distribution forecasts a significantly higher rate than reported in the Toppozada [2000] catalogue for earthquakes in the magnitude range 6-7. The same discrepancy occurred in the SCEC Phase II model, the 1996 CDMG/USGS hazard model, and others in which the maximum earthquakes size is assumed limited by fault length or area. A better fit would require significantly lower coupling (0.6 to 0.7) and substantially larger MMCE. For example, the theory and observations would agree well if the MMCE for each fault were increased by more than half a unit, or if the MMCE had a uniform value 8 and the coupling coefficient were 0.6. To consider possible effects due to large uncertainties in geologically determined fault slip rates, we are now using optimized estimates of fault slip rate to improve our estimation of MFEE. We estimate optimal slip rates for all faults in California from kinematic modeling (by finite elements) and including geologic slip rates, GPS measurements, and most compressive stress directions. Our final goal is to construct contour maps of MFEE for various P, T in California, compare with other seismic hazard approaches (geodesy, past seismicity), and test our prediction against future earthquakes.
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting