On the Relevance of the Spatial Distribution of Events for Seismic Hazard Evaluation

Seismic hazard evaluation is proposed by a methodological approach that allows thestudy of the influence of different modelling assumptions relative to the spatial andtemporal distribution of earthquakes on the maximum values of expected intensities.In particular, we show that the estimated hazard at a fixed point is very sensitive tothe assumed spatial distribution of epicentres and their estimators. As we will see, theusual approach, based on uniformly distributing the epicentres inside each seismogeniczone is likely to be biased towards lower expected intensity values. This will be mademore precise later. Recall that the term ``bias' means, that the expectation of theestimated quantity (taken as a random variable on the space of statistics) is differentfrom the expectation of the quantity itself. Instead, our approach, based on an estimatorthat takes into account the observed clustering of events is essentially unbiased, as shownby a Monte-Carlo simulation, and is configured on a 11011-isotropic macroseismicattenuation model which is independently estimated for each zone.