ALBERT

Description: Since August 2016, central Italy has been struck by one of the most important seismic sequences ever recorded in the country. In this study, a strong-motion data set, consisting of nearly 10,000 waveforms, has been analyzed to gather insights about the main features of ground motion, in terms of regional variability, shaking intensity, and near-source effects. In particular, the shake maps from the three main events in the sequence have been calculated to evaluate the distribution of shaking at a regional scale, and a residual analysis has been performed, aimed at interpreting the strong-motion parameters as functions of source distance, azimuth, and local site conditions. Particular attention has been dedicated to near-source effects (i.e., hanging wall/footwall, forward-directivity, or fling-step effects). Finally, ground-motion intensities in the near-source area have been discussed with respect to the values used for structural design. In general, the areas of maximum shaking appear to reflect, primarily, rupture complexity on the finite faults. Large ground-motion variability is observed along the Apennine direction (northwest–southeast) that can be attributed to source-directivity effects, especially evident in the case of small-magnitude aftershocks. Amplifications are observed in correspondence to intramountain basins, fluvial valleys, and the loose deposits along the Adriatic coast. Near-source ground motions exhibit hanging-wall effects, forward-directivity pulses, and permanent displacement.

Description: 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.

Description: The seismological community is currently developing operational earthquake forecasting (OEF) systems that aim to estimate, based on continuous ground motion recording by seismic networks, the rates of events exceeding a certain magnitude threshold in an area of interest and in a short-period of time (days to weeks); i.e., the seismicity. OEF may be possibly 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 paper reports the investigation about feasibility of short-term risk assessment, or operational earthquake loss forecasting (OELF), in Italy. The approach is that of performance-based earthquake engineering, where 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, and exposure data in terms of buildings per vulnerability class and occupants per building typology. All vulnerability and exposure data are at the municipality scale. The procedure set-up, which is virtually independent on the seismological model used, is implemented in an experimental OELF system, which continuously process OEF information to produce weekly nationwide risk maps. 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, on short-term risk assessment, of the methodology currently used for OEF in Italy.

Description: Published

Description: 2286-2298

Description: 3T. Pericolosità sismica e contributo alla definizione del rischio

Description: JCR Journal

Description: reserved

Description: To define reference structural actions, engineers practicing earthquake resistant design are required by codes to account for ground motion likely to threaten the site of interest and also for pertinent seismic source features. In most of the cases, while the former issue is addressed assigning a mandatory design response spectrum, the latter is left unsolved. However, in the case that the design spectrum is derived from probabilistic seismic hazard analysis, disaggregation may be helpful, allowing to identify the earthquakes having the largest contribution to the hazard for the spectral ordinates of interest. Such information may also be useful to engineers in better defining the design scenario for the structure, e.g., in record selection for nonlinear seismic structural analysis. On the other hand, disaggregation results change with the spectral ordinate and return period, and more than a single event may dominate the hazard, especially if multiple sources affect the hazard at the site. This work discusses identification of engineering design earthquakes referring, as an example, to the Italian case. The considered hazard refers to the exceedance of peak ground acceleration and 1s spectral acceleration with four return periods between 50 and 2475 year. It is discussed how, for most of the Italian sites, more than a design earthquake exists, because of the modeling of seismic sources. Furthermore, it is explained how and why these change with the limit state and the dynamic properties of the structure. Finally, it is illustrated how these concepts may be easily included in engineering practice complementing design hazard maps and effectively enhancing definition of design seismic actions with relatively small effort.

Description: Published

Description: 1212–1231

Description: JCR Journal

Description: restricted

Description: Probabilistic seismic hazard analysis allows to calculate the mean annual rate of exceedance of ground motion intensity measures given the seismic sources the site of interest is subjected to. This piece of information may be used to define the design seismic action on structures. Moreover, through disaggregation of seismic hazard, it is possible to identify the earthquake giving the largest contribution to the hazard related to a specific IM value. Such an information may also be of useful to engineers in better defining the seismic treat for the structure of interest (e.g., in record selection for nonlinear seismic structural analysis). On the other hand, disaggregation results change with the spectral ordinate and return period, and more than a single event may dominate the hazard, especially if multiple sources affect the hazard at the site. In this work disaggregation for structural periods equal to 0 sec and 1.0 sec is presented for Italy, with reference to the hazard with a 475 year return period. It will be discussed how for the most of Italian sites more than a design earthquake exist, because of the modelling of seismic sources.

Description: Unpublished

Description: Ohrid, Republic of Macedonia

Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale

Description: open

Description: I dati accelerometrici relativi alla sequenza sismica de L’Aquila, iniziata con l’evento del 6 Aprile alle ore 1.32 (MW 6.3), provengono dalla rete Rete Accelerometrica Nazionale (RAN), gestita dal Dipartimento della Protezione Civile (DPC) e da una rete temporanea installata il giorno dopo la scossa principale ad opera dell’Istituto Nazionale di Geofisica e Vulcanologia (INGV MI-PV). I dati del DPC sono scaricabili dalla banca dati accelerometrica italiana ITACA (http://itaca.mi.ingv.it), mentre quelli dell'INGV sono accessibili dal sito Internet http://accel.mi.ingv.it/statiche/ABRUZZO-2009/main.html. Il terremoto de L’Aquila è il terzo evento più forte che abbia prodotto registrazioni accelerometriche in Italia, dopo i terremoti dell’Irpinia (1980, MW 6.9) e del Friuli (1976, MW 6.4). Questo evento, insieme alle 12 repliche più forti (MW 〉 4.0) ha fornito un insieme di dati accelerometrici unico in Italia, in particolare per la presenza di un numero consistente di registrazioni in zona epicentrale ("campo vicino"). Il data set è composto da circa 300 accelerogrammi digitali (di cui 270 provenienti dalla RAN), con un ottimo rapporto segnale/rumore, registrati da circa 70 stazioni, installate in varie condizioni di sito, a distanze comprese fra 0 e 300 km. L'importanza di questo data set, non solo a livello nazionale, è legato al contributo significativo che fornisce nel colmare una lacuna nella distribuzione magnitudo-distanza dei dati strong motion italiani e mondiali, soprattutto per quanto riguarda gli eventi con meccanismo di faglia normale (Ameri et al.; 2009). I dati registrati in campo vicino provengono da un transetto composto da 6 stazioni installato dalla Protezione Civile nel 2001 nella Alta Valle dell’Aterno, con lo scopo di investigare la variabilità del moto sismico rispetto alle condizioni geologiche locali, dalla stazione AQK, installata in prossimità del centro urbano e da una stazione (AQU) appartenente alla rete broad band Mednet (http://mednet.rm.ingv.it/data.php), situata nel castello de L’Aquila. Queste stazioni distano meno di 5 km dall’epicentro dell’evento principale, ricadendo all’interno della proiezione superficiale del piano di rottura. A queste si aggiungono le registrazioni delle repliche, ottenute dalle stazioni della rete temporanea INGV, installata in area epicentrale. In questo lavoro si presenta un resoconto delle principali caratteristiche dello scuotimento del suolo verificatosi durante la sequenza sismica aquilana, attraverso l’analisi dei dati accelerometrici relativi alla scossa principale e alle due repliche più forti. Si discutono in particolare la dipendenza di diversi parametri strong motion dalla distanza, dall’azimuth e dalle condizioni di sito, e l'effetto delle caratteristiche del moto in campo vicino sulla risposta strutturale

Description: Published

Description: 57-68

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: N/A or not JCR

Description: reserved

Description: 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.