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Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2)

U.S. Geological Survey, 525 South Wilson Avenue, Pasadena, California 91106-3212 field{at}usgs.gov

T. E. Dawson

California Geological Survey

K. R. Felzer

U.S. Geological Survey, Pasadena, California

A. D. Frankel

U.S. Geological Survey, Golden, Colorado

V. Gupta and T. H. Jordan

University of Southern California

T. Parsons

U.S. Geological Survey, Menlo Park, California

M. D. Petersen

U.S. Geological Survey, Golden, Colorado

R. S. Stein

U.S. Geological Survey, Menlo Park, California

R. J. Weldon, II

University of Oregon

C. J. Wills

California Geological Survey

The 2007 Working Group on California Earthquake Probabilities (WGCEP, 2007) presents the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2). This model comprises a time-independent (Poisson-process) earthquake rate model, developed jointly with the National Seismic Hazard Mapping Program and a time-dependent earthquake-probability model, based on recent earthquake rates and stress-renewal statistics conditioned on the date of last event. The models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular, extensible Open Seismic Hazard Analysis framework. The rate model satisfies integrating measures of deformation across the plate-boundary zone and is consistent with historical seismicity data. An overprediction of earthquake rates found at intermediate magnitudes (6.5M7.0) in previous models has been reduced to within the 95% confidence bounds of the historical earthquake catalog. A logic tree with 480 branches represents the epistemic uncertainties of the full time-dependent model. The mean UCERF 2 time-dependent probability of one or more M6.7 earthquakes in the California region during the next 30 yr is 99.7%; this probability decreases to 46% for M7.5 and to 4.5% for M8.0. These probabilities do not include the Cascadia subduction zone, largely north of California, for which the estimated 30 yr, M8.0 time-dependent probability is 10%. The M6.7 probabilities on major strike-slip faults are consistent with the WGCEP (2003) study in the San Francisco Bay Area and the WGCEP (1995) study in southern California, except for significantly lower estimates along the San Jacinto and Elsinore faults, owing to provisions for larger multisegment ruptures. Important model limitations are discussed.