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Motivated by the crucial implications of Ground Motion Models in terms of seismic hazard analysis and civil protection planning, this work extends a scalar Ground Motion Model for Italy to the framework of Functional Data Analysis. The inherent characteristic of seismic data to be incomplete over the observation domain of oscillation periods entails embedding the analysis in the context of partially observed functional data and performing data reconstruction. This work proposes a novel methodology that accounts for the fact that parts of the curves are directly observed and other parts are reconstructed, thus, characterized by greater uncertainty. The method defines observation-specific functional weights, which enter the estimation process to reduce the impact that the less reliable portions of the curves have on the final estimates. The classical methods of smoothing and concurrent functional regression are extended to include weights. The advantages of the proposed methodology are assessed on synthetic data. Eventually, the weighted functional analysis performed on seismological data is shown to provide a natural smoothing and stabilization of the spectral estimates of the Ground Motion Model considered. for this article are available online. [ABSTRACT FROM AUTHOR]

The region of central Italy is well known for its moderate-to-large earthquakes. Events such as 2016 Mw 6.2 Amatrice, generated in the shallow extensional tectonic regime, motivate numerical simulations to gain insights into source-related ground-motion complexities. We utilize a hybrid integral-composite kinematic rupture model by Gallovič and Brokešová (2007) to predict ground motions for other hypothetical Amatrice fault rupture scenarios (scenario events). The synthetic seismograms are computed in 1D crustal velocity models, including region-specific 1D profiles for selected stations up to 10 Hz. We create more than ten thousand rupture scenarios by varying source parameters. The resulting distributions of synthetic spectral accelerations at periods 0.2-2 s agree with the empirical nonergodic ground-motion model of Sgobba et al. (2021) for central Italy in terms of the mean and total variability. However, statistical mixed-effect analysis of the residuals indicates that the between-event variability of the scenarios exceeds the empirical one significantly. We quantify the role of source model parameters in the modeling and demonstrate the pivotal role of the so-called stress parameter that controls high-frequency radiation. We propose restricting the scenario variability to keep the between-event variability within the empirical value. The presented validation of the scenario variability can be generally utilized in scenario modeling for more realistic physics-based seismic hazard assessment. [ABSTRACT FROM AUTHOR]

We investigated the temporal variation of the spectral decay parameter [Math Processing Error] before and after two main earthquakes that occurred in the central Italy region, namely the Amatrice ([Math Processing Error] 6.0) of 24 August 2016 and the Norcia ([Math Processing Error] 6.5) of 30 October 2016 earthquakes. For this analysis, we used seismograms from the central Italy dense seismic array stations, and earthquakes located at hypocenter distances r < 80 km, having magnitudes [Math Processing Error] 3.4-6.5. The dataset consists of 393 events recorded at 92 stations. We estimated, for both earthquake sequences, average functions [Math Processing Error] that describe the distance dependence of [Math Processing Error] along the S-wave source-station paths using acceleration spectra from foreshocks, mainshock, and aftershocks. We observed that there was a regional attenuation drop within approximately two months after the Amatrice earthquake. Then, [Math Processing Error] tends to return toward the attenuation values observed before the occurrence of the main event, namely to the values of [Math Processing Error] obtained from the foreshocks, when the earthquake cycle is probably completed. We also estimated the near-source kappa ([Math Processing Error]) using aftershocks from 24 August 2016 to 3 September 2016. The results show that the values of [Math Processing Error] are lower than those from aftershocks located to the north near the epicenter of the Amatrice earthquake, suggesting that the tectonic stress was probably high near the rupture zone, and that there may be a likely fluid flow of crustal fluids. [Math Processing Error] obtained from the foreshocks of the Norcia earthquake is like that calculated with the records of the Amatrice aftershocks. Then, [Math Processing Error] drops to lower attenuation values during the Norcia main event and tends to increase again during the aftershocks. From the analysis of these two earthquake sequences that occurred in a short-time interval in central Italy, we conclude that the temporal variation of [Math Processing Error] could be a valuable indicator to monitor the earthquake cycle. [ABSTRACT FROM AUTHOR]

Rupture directivity and its potential frequency dependence is an open issue within the seismological community, especially for small‐to‐moderate events. Here, we provide a statistical overview based on empirical evidence of seismological observations, thanks to the large amount of high‐quality seismic recordings (more than 30,000 waveforms) from Central Italy, which represents an excellent and almost unique natural laboratory of normal faulting earthquakes in the magnitude range between 3.4 and 6.5 within the time frame 2008–2018. In order to detect an anisotropic distribution of ground motion amplitudes due to the rupture directivity, we fit the smoothed Fourier Amplitude Spectra (FAS) cleared of source‐, site‐ and path‐effects. According to our criteria, about 36% of the analyzed events (162 out of 456) are directive and the distribution of rupture direction is aligned with the strikes of the major faults of the Central Apennines. We find that the directivity is a band‐limited phenomenon whose width may extend up to five times the corner frequency. The results of this research provide useful insights to parameterize directivity, to be explicitly implemented in future ground motion modeling and scenario predictions. Plain Language Summary: In seismology, directivity is one of the source phenomena that causes large spatial variability of earthquake ground motions and is related to the features of the rupture propagation along the fault. The importance of this effect is very well known for large‐magnitude events (M > 6), while it is still an open issue for small‐to‐moderate events. The aim of this paper is to recognize directive events and quantify their strength in Central Italy, using a large data set of earthquakes in the magnitude range 3.4–6.5 that occurred between 2008 and 2018. We find that about 36% of the analyzed events are directive, caused by rupture propagations oriented along the NW‐SE alignment of the Central Apennines fault systems. Furthermore, we find that directivity is a band‐limited phenomenon and that as the directivity gets stronger, the frequency band becomes wider. Our contribution provides a useful insight with the possibility to improve the parametrization of directivity within the empirical seismic hazard assessment. Key Points: Statistical procedure to detect directivity effects in small‐to‐moderate earthquakes analyzing the aleatory residuals of the ground motionThe directive events are the 36% of the data set and the distribution of rupture direction is aligned with the strikes of the faults systemThe observed directivity is a frequency‐dependent band‐limited phenomenon, which can occur up to five times the value of corner frequency [ABSTRACT FROM AUTHOR]

In this article, we implement a new approach to calibrate ground-motion models (GMMs) characterized by spatially varying coefficients, using the calibration dataset of an existing GMM for crustal events in Italy. The model is developed in the methodological framework of the multisource geographically weighted regression (MS-GWR, Caramenti et al., 2020), which extends the theory of multiple linear regression to the case with model coefficients that are spatially varying, thus allowing for capturing the multiple sources of nonstationarity in ground motion related to event and station locations. In this way, we reach the aim of regionalizing the ground motion in Italy by specializing the model in a nonergodic framework. Such an attempt at regionalization also addresses the purpose of capturing the regional effects in the modeling, which is needed for the Italian country, where ground-motion properties vary significantly across space. Because the proposed model relies on the italian GMM (ITA18) (Lanzano et al., 2019) dataset and functional form, it could be considered the ITA18 nonstationary version, thus allowing one to predict peak ground acceleration and velocity, as well as 36 ordinates of the 5%-damped acceleration response spectra in the period interval T=0.01-10 s. The resulting MS-GWR model shows an improved ability to predict the ground motion locally, compared with stationary ITA18, leading to a significant reduction of the total variability at all periods of about 15%-20%. The article also provides scenario-dependent uncertainties associated with the median predictions to be used as a part of the epistemic uncertainty in the context of probabilistic seismic hazard analyses. Results show that the approach is promising for improving the model predictions, especially on densely sampled areas, although further studies are necessary to resolve the observed trade-off inherent to site and path effects, which limits their physical interpretation. [ABSTRACT FROM AUTHOR]

We present an extended and updated version of the worldwide NEar-Source Strong-motion (NESS) flat file, which includes an increased number of moderate-to-strong earthquakes recorded in epicentral area, new source metadata and intensity measures, comprising spectral displacements and fling-step amplitudes retrieved from the extended baseline correction processing of velocity time series. The resulting dataset consists of 81 events with moment magnitude≥5.5 and hypocentral depth shallower than 40 km, corresponding to 1189 three-component waveforms, which are selected to have a maximum source-to-site distance within one fault length. Details on the flat files, metadata, and ground-motion parameters, processing scheme, and statistical findings are presented and discussed. The analysis of these data allows recognizing the presence of distinctive features (such as pulse-like waveforms, large vertical components, and hanging-wall effects) that can be exploited to assess their impact on near-source seismic motion. As an example, we use the NESS2.0 dataset for calibrating an empirical correction factor of a regional ground-motion model (GMM) mainly based on far-field records. In this way, we can adjust the median predictions to account for near-source effects not fully captured by the reference model. The final goal of this work is to promote the use of the NESS2 flat file as a tool to disseminate qualified and referenced near-source data and metadata in the light of improving the constraints of GMMs (both empirical and physics-based) close to the source. [ABSTRACT FROM AUTHOR]

This paper provides a new methodological framework to generate empirical ground shaking scenarios, designed for engineering applications and civil protection planning. The methodology is useful both to reconstruct the ground motion pattern of past events and to generate future shaking scenarios, in regions where strong‐motion datasets from multiple events and multiple stations are available. The proposed methodology combines (1) an ad‐hoc nonergodic ground motion model (GMM) with (2) a spatial correlation model for the source region‐, site‐, and path‐systematic residual terms, and (3) a model of the remaining aleatory error to take into account for directivity effects. The associated variability is a function of the type of scenario generated (bedrock or site, past or future event) and it is minimal for source areas where several events have occurred and for sites where recordings are available. In order to develop the region‐specific fully nonergodic GMM and to compute robust estimation of the residual terms, the approach is calibrated on a highly dense dataset compiled for the area of central Italy. Example tests demonstrate the validity of the approach, which allows to simulate acceleration response spectra at unsampled sites, as well as to capture peculiar physical features of ground motion patterns in the region. The proposed approach could be usefully adopted for data‐driven simulations of ground shaking maps, as alternative or complementary tool to physic‐based and stochastic‐based approaches. [ABSTRACT FROM AUTHOR]

In this study, we propose an approach to generate spatially correlated seismic ground-motion fields for loss assessment and risk analysis. Differently from the majority of spatial correlation models, usually calibrated on within-earthquake residuals, we use the sum of the source-, site-, and path-systematic effects (namely corrective terms) of the ground-motion model (GMM), obtained relaxing the ergodic assumption. In this way, we build a scenario-related spatial correlation model of the corrective terms by which adjusting the median predictions of ground motion and the associated variability. We show a case study focused on the Po Plain area in northern Italy, presenting a series of peculiar features (i.e., availability of a dense dataset of seismic records with uniform soil classification and very large plain with variable thickness of the sedimentary cover) that make its study particularly suitable for the purpose of developing and validating the proposed approach. The study exploits the repeatable corrective terms, estimated by Lanzano et al. (2017) in northern Italy, using a local GMM (Lanzano et al., 2016), which predicts the geometric mean of horizontal response spectral accelerations in the 0.01-4 s period range. Our results show that the implementation of a spatially correlated model of the systematic terms provides reliable shaking fields at various periods and spatial patterns compliant with the deepest geomorphology of the area, which is an aspect not accounted by the GMM model. The possibility to define a priori fields of systematic effects depending on local characteristics could be usefully adopted either to simulate future ground-motion scenarios or to reconstruct past events. [ABSTRACT FROM AUTHOR]

This work aims to revise the Bindi et al. (2011) ground-motion model for shallow crustal earthquakes in Italy (hereinafter, ITA10), calibrated in the magnitude range 4.0-6.9 using strong-motion data recorded up to the 2009 L'Aquila sequence. The improvement of ITA10 is needed because of the large number of strong-motion records made available in Italy after the occurrence of the most recent seismic sequences (2012 Emilia, Northern Italy; 2016-2017 Central Italy). The new data collection allows us to extend the magnitude range beyond 6.9 and to include vibration periods up to 10 s. Instead of the geometric mean of the horizontal components of ground motion, the median of orientation independent amplitudes (RotD50) is selected as a measure of the ground-motion parameters, and the rupture distance is introduced as an alternative source-to-site metric to the Joyner-Boore distance (RJB). The site effects are accounted for by a linear dependence on the time-averaged shear-wave velocity in the upper 30 m, VS30. A breakdown of the ground-motion variability is performed into between-event and site-to-site components to make the model suitable for the evaluation of nonergodic probabilistic seismic hazard. We also build a heteroscedastic model for aleatory variability as a function of moment magnitude and VS30. The evaluation of the epistemic uncertainty in the median prediction is also provided to be introduced in the logic trees for the probabilistic seismic hazard assessment. We obtain changes in median predictions with respect to ITA10 at distances lower than 10 km and for strong events (Mw>6.5); moreover, the total standard deviations are significantly lower at intermediate and long periods, with an average reduction of about 20%. [ABSTRACT FROM AUTHOR]

The 1915, M w 6.7, Fucino earthquake is one of the most destructive events occurred in the central-southern Apennines (Central Italy) in pre-instrumental era, involving normal faulting in a deep alluvial basin. This study shows the application of the empirical non-ergodic approach (NESK method) for mapping ground shaking related to this historical event, taking into account the regional features of source, propagation and site contributions. Corrections of the source-region and spatially correlated maps of site and path residuals are combined with median prediction at the reference rock (i.e. without site amplification) to generate spatially variable ground shaking and associated variability in terms of peak ground acceleration and spectral ordinates at vibration periods from 0.01s to 2s. The method captures the main spatial non-stationarities and anisotropies of the shaking fields produced by this earthquake in and around the Fucino basin. In particular, we obtain patterns of seismic motion quite in accordance with the results of other methods and the macroseismic intensity field. Marked amplifications of the shaking in the long-periods are also captured, due to the coupling of 3D site effects, especially in the deeper portion of the basin, with propagation effects mainly focused towards the eastern part of the fault. These results confirm that the non-ergodic shaking scenarios from NESK can provide useful indications even in the case of very complex seismological and geological contexts, such as in the case of strong events in deep sedimentary basins. • The shaking scenario of the 1915 Fucino event is reconstructed using a non-ergodic approach. • The empirical method maps effects on shaking due to source, site, and propagation. • Spatial non-stationarities and anisotropies of the shaking field are captured. [ABSTRACT FROM AUTHOR]

This laboratory study deals with a comprehensive investigation of modified concrete specimens using rubber particles obtained from End of Life Tyres (ELT). Different types of mixes have been studied with different percentages of rubber particles used as a partial substitute for natural aggregates by using and comparing mixtures with various types of addition and surface treatment. Three types of rubber particles (ash rubber, crumb rubber and tyre chips) have been employed in the rubberised concrete mixtures replacing partially the natural aggregates. Test results shown that the rubberised concrete mix had some appealing characteristics such as a low mass density but worse compressive strength in line with previous studies. Among the most important findings, a decline in mechanical performance was observed in rubberised concrete specimens at an age of about 60 days. Moreover, cracking and delamination phenomena occurred on the test specimens cured under moist conditions which have never been described in the literature so far. The main innovation is in description of these results regarding time-dependent degradation of rubberised concrete and in a preliminary investigation about the causes of this phenomenon. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the optimum design of tuned mass dampers (TMDs) for the seismic protection of inelastic structures. A single linear TMD is treated and is assumed to be applied to a single nonlinear degree of freedom system, described by the Bouc–Wen hysteretic model. The seismic load is modelled by a stationary filtered stochastic process to consider its intrinsic stochastic nature. The optimization problem is set by taking into consideration three different possible objective functions (OFs): the maximum of the peak structural displacement standard deviation, the average hysteretic dissipated energy of a protected building with reference to an unprotected one, and a functional damage that considers the two indexes previously described. Different numerical examples and parametric analysis are shown to confront the three optimization criteria and to determine the best tuning frequency and damping ratio of the TMDs to be used in the structure. Results confirm that the application of a TMD system reduces the amount of the hysteretic dissipated energy, which is a direct measure of damage in the structure, and so it is beneficial for the protection of buildings that develop a nonlinear behaviour under severe dynamic loadings. [Copyright &y& Elsevier]

Steel bars pitting corrosion is a process that strongly jeopardises the reliability of the reinforced concrete structures exposed to chlorides. The proper treatment of uncertainties that affects geometrical, mechanical and chemical involved parameters is for some aspects still an open question because the probabilstic approach, ordinarily adopted, presents some limitations not only when few data are available to characterise involved variables but especially when some parameters are ambiguously defined, not only in terms of distribution type. In these circumstances a possibilistic approach could respresent a reasonable alternative to perform this specific reliability analysis. In the present study, the problem parameters are modelled by using a complete fuzzy criterion and a time-dependent fuzzy safety factor is defined in order to evaluate how the residual flexural resistance is greater or less than the bending moment. Moreover, the study provides a more proper mathematical analysis of the chloride penetration into concrete. [ABSTRACT FROM AUTHOR]

Near-source effects can amplify seismic ground motion, causing large demand to structures and thus their identification and characterization is fundamental for engineering applications. Among the most relevant features, forward-directivity effects may generate near-fault records characterized by a large velocity pulse and unusual response spectral shape amplified in a narrow frequency-band. In this paper, we explore the main statistical features of acceleration and displacement response spectra of a suite of 230 pulse-like signals (impulsive waveforms) contained in the NESS1 (NEar Source Strong-motion) flat-file. These collected pulse-like signals are analyzed in terms of pulse period and pulse azimuthal orientation. We highlight the most relevant differences of the pulse-like spectra compared to the ordinary (i.e., no-pulse) ones, and quantify the contribution of the pulse through a corrective factor of the spectral ordinates. Results show that the proposed empirical factors are able to capture the amplification effect induced by near-fault directivity, and thus they could be usefully included in the framework of probabilistic seismic hazard analysis to adjust ground-motion model (GMM) predictions. [ABSTRACT FROM AUTHOR]

Abstract: This paper is focused on the comparison between different approaches in structural optimization. More precisely, the conventional deterministic optimum design, based on the assumption that the only source of uncertainty concerns the forcing input, is compared to robust single-objective and multi-objective optimum design methods. The analysis is developed by considering as case of study a single-degree-of-freedom system with uncertain parameters, subject to random vibrations and equipped with a tuned mass damper device (TMD). The optimization problem concerns the selection of TMD mechanical characteristics able to enlarge the efficiency of the strategy of vibration reduction. Results demonstrate the importance of performing a robust optimum design and show that the multi-objective robust design methodology provides a significant improvement in performance stability, giving a better control of the design solution choice. [Copyright &y& Elsevier]

In this paper we present the ground response analyses (GRA) of a site where an industrial facility is planned. Due to its location on an active normal fault system known as a relevant seismic gap, the Mt. Morrone Fault system (MMF), and at the edge of a basin filled with slow velocity continental deposits, a inter-disciplinary and non-standard approach has been applied to assess the seismic input of the dynamic numerical analyses. It includes geological, seismological, geotechnical and engineering contributions. Two fault scenarios, MMF1 and MMF2, were considered and scenario-based (SSHA) and probabilistic (time-dependent, TD, and time-independent, TI) seismic hazard (PSHA) analyses were implemented. Comparison among the spectra corresponding to the 90th percentile of the SSHA statistical distribution and the PSHA average ones shows that the SSHA MMF2 has values similar to the PSHA TD model. The SSHA 90th percentile distribution was selected as target spectra to retrieve the seismic input for GRA. Nonlinear numerical simulations of seismic wave propagation were implemented to derive surface ground motion parameters. GRA acceleration response spectra and their PGA are notably higher, and thus on the side of safety, than those obtained following the Italian code approach for seismic resistant buildings. These results confirm that a scenario-based methodology can better capture the shaking effect in near-field conditions, avoiding possibly unconservative underestimations of the seismic actions and in view of a more robust performance-based approach used by engineers for either new design and/or assessment/retrofit purposes of the built environment. • A site-specific surface ground motion analyses of a near-fault industrial site using a interdisciplinary methodology. • Similarity of response spectra for deterministic scenario-based and probabilistic time dependent seismic hazard analyses at the bedrock. • The seismic input at the bedrock from the fault scenarios, is more severe than the values predicted by the seismic resistant code for a rock site. • A fully nonlinear modeling is more appropriate than an equivalent linear one due to the high strain level induced by the scenario seismic input. [ABSTRACT FROM AUTHOR]