Hazard Map Calculations Using Grid Computing

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We present seismic-hazard maps computed using an OpenSHA (Field et al., 2003; http://www.OpenSHA.org/) application that makes use of distributed grid computing. A seismic-hazard map gives the probability that some intensity-measure level will be exceeded over a chosen time span (alternatively, one might plot the exceedance level at a particular probability). One of the two main model components needed to generate such a map is an Earthquake-Rupture Forecast (ERF), which gives a complete inventory of all possible earthquake ruptures in the region, above some magnitude threshold, and over a specified time span. The other model component is an Intensity-Measure Relationship (IMR), which gives the probability that an intensity-measure level will be exceeded at a site given the occurrence of an earthquake rupture. Examples of the latter include attenuation relationships ( e.g., Abrahamson and Shedlock, 1997), although our definition is more general to accommodate, for example, full-waveform-based IMR's. A hazard curve, which gives the exceedance probability as a function of the intensity-measure level, is then computed by considering the potential influence of all ruptures in the ERF at the site of interest (see Field et al., 2003, for details). Finally, a hazard map simply represents the spatial distribution of a point on the hazard curve. OpenSHA, which is a collaboration between the Southern California Earthquake Center (SCEC) and the U.S. Geological Survey (USGS), currently has Java applications for computing hazard curves (Field et al., 2005a), hazard spectra, scenario ShakeMaps (Field et al., 2005b), and full hazard maps (exemplified here). Because proper SHA requires that all viable, alternative models be considered in order to account for epistemic uncertainties (SSHAC, 1997), a primary goal has been to enable any new ERF or IMR to plug into these applications without having to rewrite existing code. We exemplify this “plug and play” modularity in this …