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We describe the main structure and outcomes of the new probabilistic seismic hazard model for Italy, MPS19 [Modello di Pericolosità Sismica, 2019]. Besides to outline the probabilistic framework adopted, the multitude of new data that have been made available after the preparation of the previous MPS04, and the set of earthquake rate and ground motion models used, we give particular emphasis to the main novelties of the modeling and the MPS19 outcomes. Specifically, we (i) introduce a novel approach to estimate and to visualize the epistemic uncertainty over the whole country; (ii) assign weights to each model components (earthquake rate and ground motion models) according to a quantitative testing phase and structured experts’ elicitation sessions; (iii) test (retrospectively) the MPS19 outcomes with the horizontal peak ground acceleration observed in the last decades, and the macroseismic intensities of the last centuries; (iv) introduce a pioneering approach to build MPS19_cluster, which accounts for the effect of earthquakes that have been removed by declustering. Finally, to make the interpretation of MPS19 outcomes easier for a wide range of possible stakeholders, we represent the final result also in terms of probability to exceed 0.15 g in 50 years., peer-reviewed

The zonation presented in this study has been developed with the aim of applying it as a branch of the logic tree that will be used for the new Italian seismic hazard map, presently in preparation according to the approach of seismotectonic probabilism. With respect to the zonation used for the present official seismic hazard map of Italy, the zonation proposed here considers narrower sources and is based on new and updated seismological data. In particular, some new seismogenic zones are proposed here, introducing areas that were not considered seismogenic until now (e.g., the narrow sources characterised by the presence of transform faults which are almost normal to the trend of the northern Apennines). The preliminary seismic hazard estimates produced with this new zonation aim to identify possible problems that the zonation introduces in the seismicity characterization of the seismogenic zones. As the present seismic hazard assessment was computed by considering a different attenuation model with respect to the one applied for the previous national seismic hazard maps, a re-elaboration of the most recent map referring to Italy has been developed: the comparison of the two maps is a good indicator of the areas where additional seismological investigation is needed to support the zonation presented here. In particular, some zones are not adequately documented with regard to seismicity and a different computation of the seismicity rates is suggested.

In a seismic territory, one of the concerns of the public administrators is to guarantee people’s safety in case of an earthquake occurrence, mainly in public facilities and in particular in school buildings. Public administrations are facing a complex problem and they often need to answer the following questions: what school must be adequate first? Why? What typologies of intervention are necessary? What level of safety is it possible to reach? How much is the cost of retrofitting? How many interventions can be managed with the available resources? How to manage/treat the most critical cases? How to communicate the level of risk to people? These questions point out that the definition of a rational and effective strategy for the mitigation of seismic risk implies the necessity to know the level of risk and the criticalities together with the required countermeasures and their costs. All this knowledge permits to carry out an evaluation of the needed economical effort in terms of necessary global financial amount and, consequently, the definition of the practicable strategies for risk mitigation. This problem has been addressed in the ASSESS (Analysis of the seismic scenarios of the school buildings for a definition of retrofitting priorities for seismic risk reduction) project, aimed at knowing the seismic risk of the schools of Friuli Venezia Giulia region for preventive purposes. Specific decision-making supports have been defined in order to facilitate public administrators in the management of rational seismic risk mitigation strategies.

In a seismic territory, one of the concerns of the public administrators is to guarantee people safety in case of earthquake, mainly in public facilities and in particular in school buildings. Public administrations are facing a complex problem and they need to know the level of risk and the criticalities, together with the required countermeasures and their costs, in order to define a rational and effective strategy for the mitigation of seismic risk, and consequently better allocate the resources (money and time). This problem was addressed in the ASSESS (Analysis of the Seismic ScEnarios of the School buildings for a definition of retrofitting priorities for Seismic risk reduction) project, aimed at knowing for preventive purposes the seismic risk of about 1000 school buildings of the Friuli Venezia Giulia region (north-eastern Italy). During the project, the evaluation of people safety was approached with holistic and interdisciplinary methodologies, and with multi-level studies (Figure 1). In particular, geological and geophysical studies together with vulnerability evaluations were carried out in correspondence of the school buildings. For each school a geological-technical map was developed, on which the geomorphological and hydrogeological features are represented, as these aspects can be considered potential seismic amplifiers. Furthermore, geophysical investigations were carried out in order to assess the velocity profiles to be used for evaluating the local amplification, through 1D modelling. The vulnerability assessment was done in a different way based on the level of investigation: the first level was based on a statistical approach, while a specific methodology, named VISUS, has been applied in the second level: the method, developed during the project, is based on rapid visual screening that permits the identification of weakness or critical effects in the seismic behaviour. Moreover, the vulnerability related to non-structural elements and of the egress system is provided. The ASSESS project implied the definition of decision-making supports in the form of synthesis indicators (Figure 2). In particular, a performance structural class was assigned to each school building, based on the ratio between the capacity and the demand of the structure. The membership to each class is defined, graphically, in analogy to the energy efficiency classes.Furthermore, globally considering safety, five main issues have been identified in order to take into account all the elements that can cause deaths or injuries: site, global structural, local structural, non-structural, and functional weaknesses. The results are synthesized within an “intervention requirement rose”, where the presence of one or more “petals” implies the presence of potential criticalities, while a rose without “petals” implies that the goal of “people safety” has been reached. The data in the “intervention requirement rose” are again synthesized in a single indicator: the “ASSESS safety star”, that provides a global seismic judgment of the school. Finally, it is important to remark that the decision-making support tools defined for public administrators permit to better address the resources for a more effective definition of a strategy aimed at seismic risk mitigation at a territorial scale.

It is quite usual that advances in science do not find practical application in everyday life. This is only partly true for the problem of seismic risk reduction, because the progresses in seismic hazard assessment generally enter soon into the seismic codes, i.e., guidelines for new building design. More problematic is the case of the existing buildings, where a more complex evaluation of the seismic risk should drive intervention priorities [see more discussion in Grimaz et al. (2010, 2011d) and Slejko et al. (2012)]. ASSESS was a 3-year project financed by the Civil Protection of the Friuli Venezia Giulia Region (NE Italy) in order to study the seismic risk for some relevant buildings, identified at this stage in the school buildings and to develop tools useful for a definition of retrofitting priorities for seismic risk reduction.

In a seismic territory, one of the concerns of the public administrators is to guarantee people safety in case of an earthquake occurrence, mainly in public facilities and in particular in school buildings. Public administrations are facing a complex problem and they often need to answer the following questions: what school must be adequate first? Why? What typologies of intervention are necessary? What level of safety is possible to reach? What is the cost of retrofitting? How many interventions can be managed with the available resources? How should be managed the most critical cases? How should be communicated to people the level of risk? These questions point out that the definition of a rational and effective strategy for the mitigation of seismic risk implies the necessity to know the level of risk and the criticalities together with the required countermeasures and their costs. All this knowledge permits to carry out an evaluation of the needed economical effort in terms of necessary global financial amount and, consequently, the definition of the practicable strategies for risk mitigation. This problem has been addressed in the ASSESS (Analysis of the Seismic ScEnarios of the School buildings for a definition of retrofitting priorities for Seismic risk reduction) project, aimed at knowing the seismic risk of the schools of the Friuli Venezia Giulia region, in north-eastern Italy, for preventive purposes. Specific decision-making supports have been defined in order to facilitate public administrators in the management of rational seismic risk mitigation strategies.

International audience

In order to define seismic hazard with sufficient accuracy required for engineering applications, we initiated a multidisciplinary geoscientific study offshore western Peloponnese, focusing on the Kyparissiakos Gulf. Multibeam swath bathymetry localised unstable coastal slopes, which were later investigated by high resolution seismic profiles. Sediments and crustal structures were studied by multi-channel seismic recordings and active large-offsets seismic profiling. We established an onshore/offshore local seismic array that recorded 3500 micro-earthquakes in two months, and combined the results with historical and digital seismicity data in order to understand the active crustal deformation. These findings were further combined with geological mapping and tectonic observations from onshore Peloponnese and available offshore data. All this geologic and tectonic information was coupled with evidence from the analysis of historical and recent seismicity with the aim of identifying the seismogenic sources. We have defined nine seismogenic zones in western Peloponnese that are significantly different from those published in the literature. The new zonation addresses more accurately the deformation of the crust and sediments, and is the basis for a reliable seismic hazard analysis and seismic risk assessment. We identified a large area of the northern Peloponnese and the lonian islands of Lefkas, Cephalonia, Zakynthos and Strophades, to be involved in a SW-ward oriented crustal extrusion, dominated by two major dextral deforming strike slip faults: Cephalonia and Andravida with their offshore prolongation. Some changes with respect to the Greek zonation in the literature have been introduced in the region surrounding the new nine seismogenic zones to reach a homogeneous cover of the whole Peloponnese. © 2014 - OGS.

Uno degli obiettivi perseguiti dal GNDT negli ultimi anni è stato la realizzazione della carta di pericolosità sismica del territorio nazionale a fini di riclassificazione, che è stata ufficialmente consegnata al Dipartimento della Protezione Civile nel 1996, quale prodotto finale del Progetto Triennale 1993-1995. Per la realizzazione di tale prodotto era stato deciso, dopo ampia discussione scientifica, di seguire un metodo probabilistico consolidato a livello internazionale (metodo di Cornell, 1968: MC) che fornisce le stime di pericolosità contemplate anche dal codice sismico europeo EC8. Inoltre, l’utilizzo di questo metodo consente di procedere a confronti immediati tra le pericolosità di diversi nazioni ed è stato adottato anche nell’ambito del progetto di cooperazione internazionale GSHAP. Parallelamente alla realizzazione delle carte di pericolosità sismica d'Italia secondo l’MC, scelta dal GNDT quale stima "ufficiale" della pericolosità per la riclassificazione sismica nazionale, sono stati sviluppati, sempre nell’ambito delle attività del GNDT, due nuovi metodi che hanno portato alla realizzazione di ulteriori stime della pericolosità sismica dell’intero territorio nazionale e che seguono rispettivamente un approccio di tipo misto (Grandori et al., 1984) ed uno di tipo deterministico. I risultati ottenuti con questi approcci alternativi sono stati utilizzati per un controllo delle stime "ufficiali" calcolate con l’MC.