Capturing and Limiting Groundmotion Uncertainty in Seismic Hazard Assessment: Fid-Bau Portal

Capturing and Limiting Groundmotion Uncertainty in Seismic Hazard Assessment

Bommer, Julian J. / Scherbaum, Frank

Abstract Seismic hazard assessments provide quantitative evaluations of the nature of ground shaking at a specified location that could be induced by future earthquakes. Such evaluations serve to inform engineering decisions about the location and design of new projects and the safety of existing structures. In order to provide the engineers and planners with complete information on which to base their decisions, the assessments must identify and, to the extent that is possible, quantify the associated uncertainties. There are major uncertainties associated with both the seismicity model and the ground-motion model in any seismic hazard assessment, but the uncertainties associated with the latter will generally have the larger impact on the results. Uncertainties in ground-motion prediction equations can be characterized as aleatory variability and epistemic uncertainty; the former can be directly integrated into the hazard calculations, although for very low annual exceedance frequencies it can become necessary to impose physical limits on the distribution of residuals. Epistemic uncertainty can be handled using logic-tree formulations. Combining several ground-motion prediction equations in a logic tree often requires adjustments to be made to compensate for the use of different parameter definitions; without these adjustments, the epistemic uncertainty can be grossly over- or underestimated. However, the adjustments themselves, which are often empirically derived, carry their own uncertainty and this must be included in the analyses.