Exceedance of design seismic actions during the 2016-2017 central Italy seismic sequence: sensitivity to two seismic hazard models

In Italy, seismic ground motion intensity for structural design relies on probabilistic seismic hazard analysis (PSHA). Research has shown that, even in the case of a moderate magnitude earthquake, it is expected that ground motion intensities larger than the design counterparts are observed at some sites in the epicentral region. The area where such an exceedance has possibly occurred can be assessed via ShakeMap. In the case of seismic sequences, ShakeMap envelopes allow to identify the fraction of the region of interest subjected to at least one exceedance of design seismic actions. For the 2016-2017 central Italy sequence, ShakeMap envelopes reveal that exceedance of the design intensity enforced by the current building code occurred in an area covering thousands of square kilometers, depending on the spectral and exceedance return period of the design intensity. This study quantifies the exceedance area of ground motion intensity according to the PSHA results based on two alternative PSHA models for Italy. One is that at the basis of the official PSHA for Italy adopted by the current building code, known as MPS04; the other relies on a grid-seismicity source model deriving from a set of source models recently developed for a new PSHA study for the country (MPS19). Looking at ShakeMap envelopes, it is found that the estimated exceedance area is of the same order of magnitude for the two hazard models, at least for the spectral and exceedance return periods considered herein.