ALBERT

Description: N/A

Description: Published

Description: 75-83

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

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

Description: N/A or not JCR

Description: reserved

Description: This study investigates the engineering applicability of two conceptually different finite-fault simulation techniques. We focus our attention on two important aspects: first to quantify the capability of the methods to reproduce the observed ground-motion parameters (peaks and integral quantities); second to quantify the dependence of the strong-motion parameters on the variability in the large-scale kinematic definition of the source (i.e. position of nucleation point, value of the rupture velocity and distribution of the final slip on the fault). We applied an approximated simulation technique, the Deterministic-Stochastic Method DSM, and a broadband technique, the Hybrid-Integral-Composite method HIC, to model the 1984 Mw 5.7 Gubbio, central Italy, earthquake, at 5 accelerometric stations. We first optimize the position of nucleation point and the value of rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 Hz. We found that the best model is given by a rupture propagating at about 2.65 km/s from a hypocenter located approximately at the center of the fault. In the second part of the paper we calculate more than 2400 scenarios varying the kinematic source parameters. At the five sites we compute the residuals distributions for the various strong-motion parameters and show that their standard deviations depend on the source-parameterization adopted by the two techniques. Furthermore, we show that, Arias Intensity and significant duration are characterized by the largest and smallest standard deviation, respectively. Housner Intensity results better modeled and less affected by uncertainties in the source kinematic parameters than Arias Intensity. The fact that the uncertainties in the kinematic model affects the variability of different ground-motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: open

Description: In the months following the April 6th, 2009, L’Aquila earthquake, several Italian and foreign research institutions installed dozens of seismic stations to monitor more than 100 localities with the aim of studying the local site effects in the epicentral area (upper and middle Aterno valley). The stations (accelerometers and velocimeters) have been deployed inside or very close to the inhabited areas. Among the investigated sites there are Onna, where almost the totality of the buildings collapsed, and the historic centre of L’Aquila, both towns suffering many casualties. The preliminary results for the examined sites show an extreme variability of ground motion and significant amplification for the most damaged localities.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: N/A or not JCR

Description: open

Description: Il terremoto del 6 aprile 2009 è sicuramente uno degli eventi per il quale si è avuto il maggior numero di registrazioni; questo ha fatto sì che sono diventate possibili molte analisi, anche molto particolareggiate, e tra queste il confronto tra gli spettri di risposta registrati e quelli previsti dalle recenti Norme Tecniche per le Costruzioni (rilasciate nel 2008 e in vigore in via definitiva dal 1° luglio 2009, NTC08). Questo tipo di confronto è stato sicuramente suggerito dal fatto che in alcune stazioni in area epicentrale si siano superati i valori di PGA previsti dalla mappa di riferimento della pericolosità sismica (MPS04, Gruppo di Lavoro MPS, 2004) per il periodo di ritorno di 475 anni. Viene quindi affrontato dapprima il problema se le registrazioni di un unico terremoto possono essere utilizzate per validare il modello di riferimento e se le eventuali differenze possano pertanto considerarsi significative. Viene poi analizzato il ruolo di alcuni elementi di input della valutazione della pericolosità sismica, in particolar modo le relazioni di attenuazione utilizzate, generalmente considerate poco affidabili per brevi distanze dalla faglia. Viene infine valutata la procedura adottata nella predisposizione di NTC08, che sembra aver privilegiato un migliore adattamento agli spettri a pericolosità uniforme rilasciati da INGV (http://esse1.mi.ingv.it) rispetto a considerazioni di cautela contenute sia negli stessi dati di pericolosità sismica che nella prassi corrente in molti paesi. La serie di confronti tra registrazioni accelerometriche e spettri di progetto previsti dalle NTC08 che è stata condotta suggerisce diverse chiavi di lettura che verranno presentate e discusse.

Description: Published

Description: Trieste

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

Description: open

Description: This study investigates the engineering applicability of two conceptually different finite-fault simulation techniques. We focus our attention on two important aspects: first to quantify the capability of the methods to reproduce the observed ground-motion parameters (peaks and integral quantities); second to quantify the dependence of the strong-motion parameters on the variability in the large-scale kinematic definition of the source (i.e., position of the nucleation point, value of the rupture velocity, and distribution of the final slip on the fault). We applied an approximated simulation technique, the deterministic-stochastic method and a broadband technique, the hybrid-integral-composite method, to model the 1984 Mw 5.7 Gubbio, central Italy, earthquake, at five accelerometric stations. We first optimize the position of the nucleation point and the value of the rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 Hz. We found that the best model is given by a rupture propagating at about 2:65 km=sec from a hypocenter located approximately at the center of the fault. In the second part of the article we calculate more than 2400 scenarios varying the kinematic source parameters. At the five sites we compute the residuals distributions for the various strongmotion parameters and show that their standard deviations depend on the source parameterization adopted by the two techniques. Furthermore, we show that Arias Intensity (AI) and significant duration are characterized by the largest and smallest standard deviation, respectively. Housner Intensity is better modeled and less affected by uncertainties in the source kinematic parameters than AI. The fact that the uncertainties in the kinematic model affects the variability of different ground-motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events.

Description: Published

Description: 647-663

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: L’INGV (http://www.mi.ingv.it/) svolge in Lombardia ricerche nel campo della mitigazione del rischio sismico, mediante studi mirati al miglioramento delle conoscenze sulla storia sismica, sul modello strutturale legato al regime tettonico in atto e alla definizione del moto del suolo atteso. Accanto alle indagini necessarie alla caratterizzazione sismogenetica e dei possibili effetti dello scuotimento sismico, si pone l’attività di monitoraggio sismico, che la Sezione di Milano-Pavia espleta mediante la rete accelerometrica (RAIS, http://rais.mi.ingv.it/) che consta di 20 postazioni distribuite in prevalenza sul territorio regionale. In un recente lavoro di sintesi - di studi pluriennali su fonti storiche e di revisioni critiche di materiali pubblicati - si è tentato di colmare l’evidente carenza conoscitiva sulle caratteristiche della sismicità storica dell’area lombarda. Tale carenza è particolarmente evidente se si rapportano le informazioni oggi disponibili sui terremoti del passato in quest’area con quelle relative al settore veneto-friulano. La regione analizzata, compresa tra il bacino del fiume Adda e il Lago di Garda, è stata caratterizzata da alcuni terremoti con Mw〉5.5 (es., 1117, Veronese; 1222, Brescia; 1901, Salò) e vari eventi con Mw compresa fra 4.8 e 5.5 (es., 1065, Brescia; 1396, Monza; 1642, Bergamo). Per molti degli eventi sismici fino al 1700 le informazioni sono desumibili soltanto da scarse fonti storiche. La determinazione epicentrale e l’attribuzione della magnitudo per tali eventi sono da considerarsi, pertanto, con una certa cautela al fine di definire le caratteristiche sismiche del territorio. I terremoti del 1117 e del 1222, in tale contesto, rappresentano un’eccezione rispetto ai dati generalmente disponibili. E tuttavia vari problemi tuttora aperti rendono assai difficile l’utilizzo della distribuzione del danno attribuibile a questi eventi nella prospettiva di un’affidabile parametrizzazione. Le indagini geologico-strutturali e di geologia del Quaternario, finalizzate a definire un quadro strutturale compatibile con il regime tettonico in atto, sono necessarie per giustificare la storia sismica e, in sostanza, per definire il comportamento sismogenetico della regione. Le geometrie dei sistemi di faglia attivi alpini sono ora sufficientemente noti. Le conoscenze permettono di formulare ipotesi sismotettoniche relative all’origine dei terremoti dell’area gardesana e del Bresciano. In via di definizione sono invece le geometrie dei fronti appenninici, cui sono attribuibili i terremoti al di sopra della soglia nel settore padano. Le ricerche attuali sono altresì indirizzate ad una migliore caratterizzazione del complesso settore compreso tra la parte meridionale del Lago di Garda (area di Sirmione), Verona e Mantova, all’interno del quale potrebbe collocarsi l’area epicentrale del terremoto del 1117 (o una delle aree epicentrali, qualora si considerasse questo evento come rappresentato da una sequenza sismica). Uno dei settori regionali con maggiore frequenza di eventi sismici è l’area gardesana occidentale, per questo motivo la rete di monitoraggio presenta una notevole densità di postazioni nel Bresciano e se ne è pianificato l’addensamento nel Veronese. Nel corso del 2007, la rete ha consentito la registrazione di 516 forme d’onda relative a 28 eventi locali e regionali (di cui una decina localizzati nell’area citata) con magnitudo da 1.3 a 4.2, di cui sono stati calcolati i parametri di interesse ingegneristico. L’analisi delle registrazioni ha permesso di ricavare informazioni utili per il calcolo di scenari di scuotimento. Un esempio di taali applicazioni è rappresentato dallo scenario realizzato utilizzando come terremoto di riferimento l'evento del 24 Novembre 2004 (M 5.2).

Description: Published

Description: Milano

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: In this paper, we adopt three ground-motion simulation techniques (EXSIM, Motazedian and Atkinson, 2005, DSM, Pacor et al., 2005 and HIC, Gallovič and Brokešová, 2007), with the aim of investigating the different performances in near-fault strong-motion modeling and prediction from past and future events. The test case is the 1980, M 6.9, Irpinia earthquake, the strongest event recorded in Italy. First, we simulate the recorded strong-motion data and validate the model parameters by computing spectral acceleration and peak amplitudes residual distributions. The validated model is then used to investigate the influence of site effects and to compute synthetic ground motions around the fault. Afterward, we simulate the expected ground motions from scenario events on the Irpinia fault, varying the hypocenters, the rupture velocities and the slip distributions. We compare the median ground motions and related standard deviations from all scenario events with empirical ground motion prediction equations (GMPEs). The synthetic median values are included in the median ± one standard deviation of the considered GMPEs. Synthetic peak ground accelerations show median values smaller and with a faster decay with distance than the empirical ones. The synthetics total standard deviation is of the same order or smaller than the empirical one and it shows considerable differences from one simulation technique to another. We decomposed the total standard deviation into its between-scenario and within-scenario components. The larger contribution to the total sigma comes from the latter while the former is found to be smaller and in good agreement with empirical inter-event variability.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: restricted

Description: In the last few years in Italy many ground motion prediction equations (hereinafter GMPEs) were calibrated both at national and regional scale using weak and strong motion data recorded in the last 30 years by several networks. Moreover, many of the strongest Italian earthquakes were included in global data sets in order to calibrate GMPEs suitable for the prediction of ground-motion at very large scale. In the last decade, the Sabetta and Pugliese (1996) relationships represented a reference point for ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by Italian Accelerometric Network, and more recently by other regional networks (e.g., RAIS, Strong motion network of northern Italy), are collected in ITACA (ITalian ACcelerometric Archive). Considering Italian strong-motion data with Mw≥4.0 and distance (Joyner-Boore or epicentral) up to 100 km, new GMPEs were developed by Bindi et al. (2010), aimed at replacing the older Italian relationships. The occurrence of the recent December 23, 2008, Mw 5.4, Parma (northern Italy) earthquake and the April 6, 2009, Mw 6.3, L’Aquila earthquake, allowed us to upgrade the ITACA data set and gave us the possibility of validating the predictive capability of many GMPEs, developed using Italian, European and global data sets. The results are presented in terms of quality of performance (fit between recorded and predicted values) using the maximum likelihood approach as explained in Spudich et al. (1999). Considering the strong-motion data recorded during the L’Aquila sequence, the considered GMPEs on average, overestimate the observed data, showing a dependence of the residuals with distance in particular at higher frequencies. An improvement of fit is obtained comparing all Italian strong-motion data included in ITACA with the European GMPEs calibrated by Akkar and Bommer (2007a, 2007b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, the Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies.

Description: Published

Description: 37-53

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: 5.2. TTC - Banche dati di sismologia strumentale

Description: JCR Journal

Description: reserved

Description: This article describes the results of a ground motion modeling study of the 1915 Avezzano earthquake. The goal was to test assuinptions regarding the rupture process of this earthquake by attempting to model the damage to historical monuments and populated habitats during the earthquake. The methodology used combines stochastic and deterministic modeling techniques to synthesize strong ground motion, starting from a simple characterization of the earthquake source on an extended fault plane. The stochastic component of the methodology is used to simulate high-frequency ground motion oscillations. The envelopes of these synthetic waveforms, however, are simulated in a deterministic way based on the isochron formulation for the calculation of radiated seismic energy. Synthetic acceleration time histories representative of ground motion experienced at the towns of Avezzano, Celano, Ortucchio, and Sora are then analyzed in terms of the damage to historical buildings at these sites. The article also discusses how the same methodology can be adapted to efficiently evaluate various strong motion parameters such as duration and amplitude of ground shaking, at several hundreds of surface sites and as a function of rupture process. The usefulness of such a technique is illustrated through the inodeling of intensity data from the Avezzano earthquake. One of the most interesting results is that it is possible to distinguish between different rupture scenarios for the 1915 earthquake based on the goodness of fit of theoretical intensities to observed values.

Description: JCR Journal

Description: open

Description: In this paper, we adopt three ground‐motion simulation techniques (EXSIM, Motazedian and Atkinson, 2005, DSM, Pacor et al., 2005 and HIC, Gallovič and Brokešová, 2007), with the aim of investigating the different performances in near‐fault strong‐motion modeling and prediction from past and future events. The test case is the 1980, M 6.9, Irpinia earthquake, the strongest event recorded in Italy. First, we simulate the recorded strong‐motion data and validate the model parameters by computing spectral acceleration and peak amplitudes residual distributions. The validated model is then used to investigate the influence of site effects and to compute synthetic ground motions around the fault. Afterward, we simulate the expected ground motions from scenario events on the Irpinia fault, varying the hypocenters, the rupture velocities and the slip distributions. We compare the median ground motions and related standard deviations from all scenario events with empirical ground motion prediction equations (GMPEs). The synthetic median values are included in the median ± one standard deviation of the considered GMPEs. Synthetic peak ground accelerations show median values smaller and with a faster decay with distance than the empirical ones. The synthetics total standard deviation is of the same order or smaller than the empirical one and it shows considerable differences from one simulation technique to another. We decomposed the total standard deviation into its between‐scenario and within‐scenario components. The larger contribution to the total sigma comes from the latter while the former is found to be smaller and in good agreement with empirical inter‐event variability.

Description: Published

Description: 1136-1151

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: open