Updating of a Psha Based on Bayesian Inference With Historical Macroseismic Intensities

Abstract eng:
Since the basic work of Cornell, many studies have been conducted in order to evaluate the probabilistic seismic hazard (PSHA) at a given site or at a regional scale. In general, results of such studies are used as inputs for regulatory hazard maps or for risk assessments. Such approaches are nowadays considered as well established and come more and more used worldwide, generally in addition to deterministic approaches. Nevertheless, some discrepancies have been observed recently in some PSHA, especially from studies conducted in areas with low to moderate seismicity. The lessons learnt from these results lead to conclude that, due to uncertainties inherent to such a domain (for example, the ground-motion prediction equations used in computing the hazard), some deterministic choices have to be made and, depending on expert judgments, may lead to strong differences in terms of seismic motion evaluation. In this context, the objective of this paper is to present a methodology that can be used to take into consideration historical observations (such as macroseismic Intensities) in order to reduce epistemic uncertainties in a probabilistic seismic hazard assessment (PSHA). The method developed here is based on a Bayesian inference technique that is used in order to quantify the likelihood of the prior estimation and finally, update the PSHA. Hazard curves (rate of occurrence of PGA), output of a given PSHA, are transformed into macroseismic Intensity through “PGAto-intensity” relationships. Random and epistemic uncertainties included in such relationships are propagated in the overall updating process, as well as the random occurrence of events, over the period of observation. The period of observation under consideration is the completeness period for each intensity data set. The updating process is developed at a regional scale over a significant number of stations. The potential correlation between points of observation is also discussed and accounted for. Finally, a case of application is proposed on the French metropolitan territory to demonstrate the efficiency of this updating method and draw perspectives for further applications.

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