Intensity-based seismic risk assessment

Abstract

Recent experience suggests that the bulk of modern studies of seismic hazard have sought to express ground motion in terms of physical parameters such as peak ground acceleration, spectral acceleration, and so on. The correlation of physical ground motion parameters with actual levels of damage has proved a difficult subject of study. No single ground motion parameter (such as peak ground acceleration) provides an ideal analogue of damage. However, the problems can be bypassed by using earthquake intensity in place of physical ground motion parameters. Intensity relates specifically to damage in a way that parameters like peak ground acceleration do not. The passage from hazard to risk is still problematic using older intensity scales, but since the MSK and the EMS-98 (European Macroseismic Scale) intensity scales directly express the probabilistic nature of damage distributions for any intensity degree, the task is greatly simplified. An equation that expresses the attenuation of EMS intensities is a description of the extent to which damage patterns to different building types vary as a function of magnitude and distance. Such an equation is based directly on past observations of damage, and so it is only natural to expect it to do a reasonable job of predicting future levels of damage. Risk curves can be prepared that show the probability of different grades of damage being suffered by buildings of different types.