Abstract
Seismic hazard maps from probabilistic seismic hazard analysis or PSHA collect, at different sites, the values of the (site-specific) ground motion intensity measures of interest that, taken individually, have the same exceedance return period. For large-scale analyses, a widely used intensity measure is the macroseismic (MS) intensity, that provides an assessment of the earthquake effect based on the observed consequences in the hit area. Hazard maps can be developed in terms of MS intensity, and some examples exist in this respect. In the case of Italy, the last MS hazard map is based on the same seismic source model (known as MPS04) adopted to derive the design seismic actions of the current building code, a study dating more than ten years ago. It provides results in terms of countrywide Mercalli–Cancani–Sieberg (MCS) intensity level with 475 years return period. This short paper presents and discusses MCS probabilistic seismic hazard maps for Italy based on a recent grid-seismicity source model, herein named MPS19, synthetizing the large effort of a wide scientific community. The results, which are obtained by means of classical PSHA, are given in the form of maps referring to the 475 years return period, and also others of earthquake engineering interest. Moreover, it is discussed that the return period does not univocally identifies the MS intensity because, although MS is, by definition, a discrete random variable, it is modelled, in a given earthquake, by means of a normal distribution, that is, treated as continuous. Thus, the maps of the minimum return period causing the occurrence or exceedance of different MCS intensities are also provided. Finally, the comparison between the 475 years return period hazard map presented and the one which is currently the point of reference in Italy, that is, computed using MPS04, is briefly discussed. All the computed maps are made available to the reader as supplemental material.
Highlights
Macroseismic (MS) intensity provides a proxy for the impact of an earthquake based on its implications observed on the affected communities, built environment and structures (e.g., Grünthal 1998)
The Italian seismic catalog, so-called Catalogo Parametrico dei Terremoti Italiani or CPTI (Rovida et al 2020), contains information, such as magnitude and location, about earthquakes occurred from 1000 AD to the end of 2017, most of which are retrieved based on macroseismic intensity estimates being no instrumental data available at the time of occurrence
To help the discussion of the results presented it is worth recalling that grades from I to V represent earthquakes that may be felt by human beings but not producing structural damage
Summary
Macroseismic (MS) intensity provides a proxy for the impact of an earthquake based on its implications (macroscopically) observed on the affected communities, built environment and structures (e.g., Grünthal 1998). MS intensity may serve to express the vulnerability of existing structures in an area of interest, based on empirical observations (e.g., Giovinazzi and Lagomarsino 2004) In those areas where the seismic monitoring network is sparse or even absent, the observed MS intensity can be used to infer ground motion IMs (e.g., peak ground acceleration; Faenza and Michelini 2010; Gomez-Capera et al 2020) or to estimate the occurred event magnitude (e.g., Sibol et al 1987; Azzaro et al 2011). The Italian seismic catalog, so-called Catalogo Parametrico dei Terremoti Italiani or CPTI (Rovida et al 2020), contains information, such as magnitude and location, about earthquakes occurred from 1000 AD to the end of 2017, most of which are retrieved based on macroseismic intensity estimates (i.e., effects assessed according to the historical evidences as provided by dedicated studies; e.g., Boschi et al 2000) being no instrumental data available at the time of occurrence. The first earthquake of the catalog for which early instrumental data are available dates back to 1918 (Sandron et al 2014) but, until the second half of sixties of the last century, the majority of the earthquakes’ magnitude estimations are based on historical information
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