HR: 15:25h
AN: S13C-07    [Abstracts]
TI: Planning for earthquakes with lifetime in mind
AU: * Jackson, D D
EM: djackson@ucla.edu
AF: Department of Earth and Space Sciences, UCLA, 595 Young Drive E., Los Angeles, CA 90095-1567 United States
AU: Mualchin, L
EM: lalliana_mualchin@dot.ca.gov
AF: California Department of Transportation, Division of Engineering Services, PO Box 168041, Sacramento, CA 95816-8041 United States
AU: Black, N
EM: nblack@ess.ucla.edu
AF: Department of Earth and Space Sciences, UCLA, 595 Young Drive E., Los Angeles, CA 90095-1567 United States
AB: What is the largest earthquake likely to occur, with allowable probability P, on a given fault during the planned lifetime T of a structure? This question is appropriate for planning because it considers both the time period for which protection is needed, and the importance of that protection through the probability P. We approach this problem by considering the magnitude-frequency distribution of earthquakes on the fault, and solving for that magnitude that corresponds to the specified time and probability requirements. The resulting magnitude, which we call the Functional Evaluation Earthquake (or FEE for short) depends on the moment rate (from the length, width, and slip rate), and maximum magnitude on the fault, as well as the assumed magnitude-frequency distribution. The moment rate is measurable directly, but the maximum magnitude can only be estimated indirectly. Assuming a density-truncated Gutenberg-Richter magnitude-frequency distribution and Poissonian recurrence, we've calculated the FEE magnitude for about 275 faults in California. When the time period T is taken to be very long, or the allowable probability P very small, the FEE approaches the maximum magnitude asymptotically as expected. Sensitivity tests show that the FEE magnitude is very stable: Uncertainty of a few units in maximum magnitude typically results in uncertainty of a half unit or less in FEE. This stability is important because the maximum magnitude is one of the most uncertain features of earthquake hazard calculations, but the FEE magnitude does not depend on it much. Why? The FEE magnitude depends on both the a-value and the maximum magnitude; for fixed moment rate, the a-value decreases when the maximum magnitude increases. The bottom line: the FEE magnitude answers an appropriate question, and it depends more on measurable quantities than the maximum magnitude.
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005