HR: 09:45h
AN: S21C-08    [Abstracts]
TI: Prospective Tests of Southern California Earthquake Forecasts
AU: * Jackson, D D
EM: djackson@ucla.edu
AF: UCLA, 595 Young Dr. East, Los Angeles, CA 90095-1567 United States
AU: Schorlemmer, D
EM: danijel@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, CH 8093 Switzerland
AU: Gerstenberger, M
EM: M.Gerstenberger@gns.cri.nz
AF: IGNS, 69 Gracefield Road, PO Box 30-368, Lower Hutt, 0000 New Zealand
AU: Kagan, Y Y
EM: kagan@cyclop.ess.ucla.edu
AF: UCLA, 595 Young Dr. East, Los Angeles, CA 90095-1567 United States
AU: Helmstetter, A
EM: agnes@ldeo.columbia.edu
AF: UCLA, 595 Young Dr. East, Los Angeles, CA 90095-1567 United States
AU: Wiemer, S
EM: stefan@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Zurich, CH 8093 Switzerland
AU: Field, N
EM: field@caltech.edu
AF: USGS, 595 Wilson Ave., Pasadena, CA 91106 United States
AB: We are testing earthquake forecast models prospectively using likelihood ratios. Several investigators have developed such models as part of the Southern California Earthquake Center's project called Regional Earthquake Likelihood Models (RELM). Various models are based on fault geometry and slip rates, seismicity, geodetic strain, and stress interactions. Here we describe the testing procedure and present preliminary results. Forecasts are expressed as the yearly rate of earthquakes within pre-specified bins of longitude, latitude, magnitude, and focal mechanism parameters. We test models against each other in pairs, which requires that both forecasts in a pair be defined over the same set of bins. For this reason we specify a standard "menu" of bins and ground rules to guide forecasters in using common descriptions. One menu category includes five-year forecasts of magnitude 5.0 and larger. Contributors will be requested to submit forecasts in the form of a vector of yearly earthquake rates on a 0.1 degree grid at the beginning of the test. Focal mechanism forecasts, when available, are also archived and used in the tests. Interim progress will be evaluated yearly, but final conclusions would be made on the basis of cumulative five-year performance. The second category includes forecasts of earthquakes above magnitude 4.0 on a 0.1 degree grid, evaluated and renewed daily. Final evaluation would be based on cumulative performance over five years. Other types of forecasts with different magnitude, space, and time sampling are welcome and will be tested against other models with shared characteristics. Tests are based on the log likelihood scores derived from the probability that future earthquakes would occur where they do if a given forecast were true [Kagan and Jackson, J. Geophys. Res.,100, 3,943-3,959, 1995]. For each pair of forecasts, we compute alpha, the probability that the first would be wrongly rejected in favor of the second, and beta, the probability that the second would be wrongly rejected in favor of the first. Computing alpha and beta requires knowing the theoretical distribution of likelihood scores under each hypothesis, which we estimate by simulations. In this scheme, each forecast is given equal status; there is no "null hypothesis" which would be accepted by default. Forecasts and test results will be archived and posted on the RELM web site. Major problems under discussion include how to treat aftershocks, which clearly violate the variable-rate Poissonian hypotheses that we employ, and how to deal with the temporal variations in catalog completeness that follow large earthquakes.
DE: 7223 Seismic hazard assessment and prediction
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting