title: Earthquake and tsunami forecasts: relation of slow slip events to subsequent earthquake rupture.
abstract: The 5 September 2012 M(w) 7.6 earthquake on the Costa Rica subduction plate boundary followed a 62-y interseismic period. High-precision GPS recorded numerous slow slip events (SSEs) in the decade leading up to the earthquake, both up-dip and down-dip of seismic rupture. Deeper SSEs were larger than shallower ones and, if characteristic of the interseismic period, release most locking down-dip of the earthquake, limiting down-dip rupture and earthquake magnitude. Shallower SSEs were smaller, accounting for some but not all interseismic locking. One SSE occurred several months before the earthquake, but changes in Mohr-Coulomb failure stress were probably too small to trigger the earthquake. Because many SSEs have occurred without subsequent rupture, their individual predictive value is limited, but taken together they released a significant amount of accumulated interseismic strain before the earthquake, effectively defining the area of subsequent seismic rupture (rupture did not occur where slow slip was common). Because earthquake magnitude depends on rupture area, this has important implications for earthquake hazard assessment. Specifically, if this behavior is representative of future earthquake cycles and other subduction zones, it implies that monitoring SSEs, including shallow up-dip events that lie offshore, could lead to accurate forecasts of earthquake magnitude and tsunami potential.
authors.affiliation: School of Geosciences, University of South Florida, Tampa, FL 33620; thd@usf.edu.
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Dixon
authors.affiliation: Pacific Geoscience Centre, Geological Survey of Canada, BC, Canada V8L 4B2;
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: School of Geosciences, University of South Florida, Tampa, FL 33620;
authors.forename: Rocco
authors.initials: R
authors.lastname: Malservisi
authors.affiliation: Department of Geology, Portland State University, Portland, OR 97201; and.
authors.forename: Robert
authors.initials: R
authors.lastname: McCaffrey
authors.affiliation: School of Geosciences, University of South Florida, Tampa, FL 33620;
authors.forename: Nicholas
authors.initials: N
authors.lastname: Voss
authors.affiliation: Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional, Heredia 3000, Costa Rica.
authors.forename: Marino
authors.initials: M
authors.lastname: Protti
authors.affiliation: Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional, Heredia 3000, Costa Rica.
authors.forename: Victor
authors.initials: V
authors.lastname: Gonzalez
keywords: GPS; earthquake; slow slip events; tsunami