Seismic hazard versus design accelerograms

The developments presented herewith arise from the legitimate wish and task of structural engineers of performing consistent analyses of risk and safety for works located in seismic regions. The paper adopts a probabilistic viewpoint, or philosophy. The starting point of this discussion is based on well – established approaches, while at the same time addressing specific research problems that could represent the task of the future, even if not an immediate one. The main topics are as follows: a brief view of (3-rd level) probabilistic safety and risk analysis, based on simplifying assumptions, which serves as a starting point for subsequent developments; a review of seismic action and hazard representation from two perspectives: ground motion during one event (advocating design accelerograms and stochastic models) and recurrence of successive events (considering, after the usual 1D approach, a generalized approach based on the consideration of a multi-dimensional space of characteristic action parameters); the development of a multi-dimensional stochastic model of ground motion (basically for a half-space consisting of successive horizontal homogeneous layers); a brief discussion of alternative possible objectives of engineering safety analyses.