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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 risk assessment for a building portfolio or a spatially distributed infrastructure requires multi-site probabilistic seismic hazard analysis (MSPSHA). In fact, MSPSHA accounts for the stochastic dependency between the ground motion intensity measures (IMs) at the sites. Multi-site hazard needs to define the correlation structure for the same IM at different sites (spatial correlation), that of different IMs at the same site (cross-correlation) and that of different IMs at different sites (spatial-cross-correlation). Literature shows that such models usually require a significant amount of regional data to be semi-empirically calibrated. An approximated yet simpler-to-model alternative option is the conditional-hazard approach. The latter, originally developed for single-site analyses as an alternative to vector-valued PSHA, allows computing the distribution of a secondary IM given the occurrence or exceedance of a value of a primary IM. Conditional hazard considers the spatial correlation of the primary IM and the cross-correlation at each site for the two IMs, thus, if it is adopted for MSPSHA, the spatial correlation of the secondary IM as well as the spatial-cross-correlation between the two IMs descends from these two models. In the study, the conditional hazard procedure for MSPSHA is discussed and implemented in an illustrative application. Results in terms of distribution of the total number of exceedances of selected thresholds at the sites in a given time interval are compared with the case of complete formulation of MSPSHA and the differences are quantified. It appears that conditional hazard is a solid, yet simpler alternative for MSPSHA, at least in the considered cases.

This paper assesses the reliability of code-compliant linear and nonlinear dynamic analyses for irregular buildings with base isolation system (BIS). Comprehensive analyses are carried out for a case study comprising a large reinforced concrete multi-storey framed hospital with 327 high-damping rubber bearings. Spectral and time history (linear and nonlinear) analyses were performed on the three-dimensional (3D) finite element model (FEM) of the structure; simplified analyses were also conducted on single-degree-of-freedom (SDOF) systems. It is found that, at damageability limit state, the values of maximum interstorey drifts (d/h) computed with spectral analyses on the three-dimensional FEM range between 1/6 and 1/10 of the code limit (d/h = 0.33%); thus more stringent code limits should be required for buildings with BISs. The maximum floor acceleration is reduced by about 70% with respect to the ground acceleration (free field site); the acceleration profile is uniform along the height of the multi-storey frame. Threshold values of floor accelerations to assess the seismic performance of equipments in buildings with BIS are lacking. At ultimate limit state (ULS), spectral analyses provide values of actions and deformations that are less conservative than those derived through time history analyses. To perform reliable dynamic analyses of base isolated buildings it is crucial to select natural earthquake ground motions compliant with the fundamental period of vibration of the structural system. Nevertheless, it is not straightforward to select adequate natural strong motions in the catalogues available world-wide; buildings incorporating BISs possess periods of vibration which are generally higher than 2.0 s. As a result, distant and high-magnitude earthquakes are effective for base isolated buildings; nevertheless, such earthquakes are scarce in the seismic databases. The outcomes of the present study also demonstrate that simplified linear analyses tend to provide estimates of the response quantities, displacements of base isolators and base shear of the superstructure, which can be reliably employed at preliminary design stage. Spectral analysis results of the 3D model tend to match those of the SDOF systems, even for irregular superstructure, provided that modal mass participating ratios are greater than 85-90%. The results of spectral analyses on both SDOF and three-dimensional FEM envelope the outcomes of linear time histories

The joint probability distribution of different intensity measures (Formula presented.) at different sites in one earthquake is needed to define the stochastic process regulating the exceedance (in time) of the (Formula presented.) at the ensemble of the sites, which in turn is a funding element of the so-called multi-site probabilistic seismic hazard analysis (MSPSHA). The simplest model for the joint distribution of the (Formula presented.) in one seismic event requires the mean vector and the covariance matrix of the (Formula presented.) at all sites, conditional to the magnitude and location of the earthquake, which may need a large amount of data to be calibrated. The conditional hazard (CH) approach, originally developed for single-site surrogate vector-valued probabilistic seismic hazard analysis, may be a simplified option for MSPSHA, as it explicitly models only part of the covariance matrix of the (Formula presented.) at the sites, while the rest forcefully follows the working assumptions. The presented paper compares the CH approach for MSPSHA against the benchmark in which the complete covariance matrix is modelled, using a testbed in which one-hundred sites are considered. When the comparison metric is the probability of a given number of (Formula presented.) exceedances observed at the sites in some time intervals, it is found that CH is a viable alternative to MSPSHA, although the degree of approximation is sensitive to which and how many (Formula presented.) are considered (e.g., which spectral acceleration). When the analysis is taken all the way to the risk, considering the fragilities of a portfolio of hypothetical buildings, and taking as the metric the probability of observing a given number of structural failures in a time interval, it is found that the approximation introduced by CH with respect to the benchmark is further reduced.

Data communication networks have large importance for the immediate post-earthquake emergency management and community resilience. In this study, the framework of simulation-based probabilistic seismic risk analysis of data communication infrastructure is applied to the real case of the inter-university data network of the Campania region (southern Italy). The network is constituted by point-like facilities (racks located within buildings and containing the device routing and managing traffic) and distributed links (buried fiber optic cables). The seismological, geological, and geotechnical features of the region were characterized together with the seismic vulnerability of each element of the network. The network performance is quantified in terms of traffic loss before and after the seismic event. Results are provided in terms of annual rate of events exceeding traffic loss thresholds and allow to identify the portion of the network mostly contributing to the seismic performance.

The dynamic behaviour of rigid blocks subjected to support excitation is represented by discontinuous differential equations with state jumps. In the numerical simulation of these systems, the jump times corresponding to the numerical trajectory do not coincide with the ones of the given problem. When multiple state jumps occur, this approximation may affect the accuracy of the solution and even cause an order reduction in the method. Focus here is on the error behaviour in the numerical dynamic. The basic idea is to investigate how the error propagates in successive impacts by decomposing the numerical integration process of the overall system into a sequence of discretized perturbed problems.

Earthquakes are generally clustered, both in time and space. Conventionally, each cluster is made of: foreshocks, the mainshock, and aftershocks. Seismic damage can possibly accumulate because of the effects of multiple earthquakes in one cluster and/or because the structure is unrepaired between different clusters. Typically, the performance-based earthquake engineering (PBEE) framework neglects seismic damage accumulation. This is because: (a) probabilistic seismic hazard analysis (PSHA) only refers to mainshocks and (b) classical fragility curves represent the failure probability in one event, of given intensity, only. However, for life-cycle assessment, it can be necessary to account for the building-up of seismic losses because of damage in multiple events. It has been already demonstrated that a Markovian model (i.e., a Markov chain), accounting for damage accumulation in multiple mainshocks, can be calibrated maintaining PSHA from the classical PBEE framework, and replacing structural fragility with a set of state-dependent fragility curves. In fact, the Markov chain also works when damage accumulates in multiple aftershocks from a single mainshock of known magnitude and location, if aftershock-PSHA replaces classical PSHA. Herein this model is extended further developing a Markovian model that accounts, at the same time, for damage accumulation: (i) within any mainshock-aftershock seismic sequence and (ii) among multiple sequences. The model is illustrated through applications to a series of six-story reinforced-concrete moment-resisting-frame buildings designed for three sites with different seismic hazard levels in Italy. The time-variant reliability assessment results are compared to the classical PBEE approach and the accumulation model that only considers mainshocks, so as to address the relevance of aftershocks for life-cycle assessment.

In the last few years, a growing interest towards structural safety of existing infrastructures has been paid. Due to very large number of structures, the scientific community is asked to provide innovative solutions that are both sustainable and reliable from the economical as well as technical point of view. This paper presents the case of Quarto bridge, selected as case study in an Italian research project for Risks and Safety Management of Infrastructures at Regional Scale (GRISIS). The structure is a railway viaduct on an urban train line, located in the Northern metropolitan area of Naples. It consists of 45 simply-supported prestressed girders sustained by reinforced concrete piers, for a total length of approximately one kilometer. According to the project, the viaduct was equipped with an on-site monitoring system for near-real-time mitigation of seismic risk. The system involves some innovative, low-cost, sensors developed and installed to be tested on the field. This paper describes the monitoring system and the implemented strategies for risk mitigation referring to a single beam-column system but its application can be potentially replicated and implemented for large scale mitigation strategies.

The seismic risk assessment of spatially distributed infrastructures is gaining increasing research attention. Data communication networks, although less investigated than other infrastructures, have large importance for the immediate post-event emergency management and community resilience. In this study the framework of simulation-based probabilistic seismic risk analysis of data communication infrastructures is applied to a real case study; i.e., the interuniversity data network of the Campania region (southern Italy). The network is constituted by point-like facilities, that is, racks located within buildings and containing the devices routing and managing traffic, and distributed links, that is, buried fiber-optic cables. The network performance was assessed following the performance-based earthquake engineering framework extended to spatially distributed systems. The seismological, geological and geotechnical features of the region were characterized together with the seismic vulnerability of each element of the network. Moreover, to overcome the absence of available fragilities for buried fiber-optic cables, and as a difference with respect to previous work of the authors on the topic, the fragilities recently developed for buried electrical cables are adapted. The network performance is quantified in terms of traffic lost, that is the difference between traffic transferred through the network before and after the seismic event. Results indicate a relatively low level of losses when the network’s region is hit by an earthquake and, according to the adopted models, a low influence of cables fragility on the performance of the network.

The seismological community is currently developing operational earthquake forecasting (OEF) systems that aim to estimate the seismicity in an area of interest, based on continuous ground‐motion recording by seismic networks; the seismicity may be expressed, for example, in terms of rates of events exceeding a certain magnitude threshold in a short period of time (days to weeks). OEF possibly may be used for short‐term seismic risk management in regions affected by seismic swarms only if its results may be the input to compute, in a probabilistically sound manner, consequence‐based risk metrics. The present article reports on the feasibility of short‐term risk assessment, or operational earthquake loss forecasting (OELF), in Italy. The approach is that of performance‐based earthquake engineering, in which the loss rates are computed by means of hazard, vulnerability, and exposure. The risk is expressed in terms of individual and regional measures, which are based on short‐term macroseismic intensity (or ground‐motion intensity) hazard. The vulnerability of the built environment relies on damage probability matrices empirically calibrated for Italian structural classes; the exposure is represented in terms of buildings per vulnerability class and occupants per building typology. All vulnerability and exposure data are at the municipality scale. The developed procedure, which is virtually independent of the seismological model used, is implemented in an experimental OELF system that continuously processes OEF information to produce nationwide risk maps applying to the week after the OEF data release. This is illustrated by a retrospective application to the 2012 Pollino (southern Italy) seismic sequence, which provides insights on the capabilities of the system and on the impact of the methodology currently used for OEF in Italy on short‐term risk assessment.

Stochastic modeling of structural deterioration at the scale of the life - cycle is the subje ct of the study . The categories of degradation phenomena considered are those two typical of structures, that is , co n- tinuous degradation of mechanical characteristics (i.e., aging ) a nd cumulative damage due to point overloads ( i.e., earthquakes ) . The wearing structural parameter is the seismic capacity expressed in terms of kinematic ductility to conventional collapse. The gamma distribution is considered to model damages produced by earthquakes and a c lose d - form approximation for structural reliabilit y assessment is obtained. Moreover, a gamma stochastic process is considered for continuous deterioration. F inally, the possible transformation of the repeated - shock effect due to earthquakes in an equivalent aging ( i.e., forward virtual age ) , leading to a close - form for the superposition of the two processes, is discussed. An e xample , referring to a simple bilinear elastic - perfectly - plastic system , illustrate s potential applicability and limitations of the approach within the performance - based earthquake e ngineering framework.

The purpose of this paper is to critically review some history - dependent probabilistic mainshoc k occurrence models with respect to probabilistic seismic hazard analysis (PSHA) . In PSHA , eart h- quake occurrence is usually referred to homogeneous Poisson process (HPP) , which is memory - less ; h owe v- er, when a single fault is of concern and/or the time scal e is different from that of the long term, history - dependent models, may be appropriate. In the study, two categories of models are reviewed : (i) renewal pr o- cesses , which are used to model the sequence of interarrival times of characteristic earthquakes , a nd (ii) si m- ple M arkov renewal processes , in which beyond earthquake occurrence, modeling of correlation between magnitude and interarrival time is also explicitly addressed . As an illustrative application, the Paganica fault (in central Italy) is considere d to compute the seismic hazard , in terms of exceedance pro b ability of a ground motion intensity measure value , according to each of the models rendered comparable by means of working hypotheses . Results show that as larger is the time since the last earth quake the more different hazard is i m- plied by the different models , rendering critical their selection for sources where the time since the last event is large .