Site Effects in the Eastern Po Plain by Mean of Weak and Strong Earthquakes

We present the activities carried out within the S2 2012-2013 Project, funded in the frame of DPCINGV Agreement, that concerns the mid-long term Seismic Hazard Assessment in Italy on two priority areas, the Po Plain and the Southern Italy. The Po Valley, an area hitherto considered of low seismological interest, has attracted the attention of the seismological community following the events of May 20, 2012. The day after the main shock that stuck eastern Emilia in 2012, the OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale deployed a temporary seismographic network in the Ferrara area. All the investigated locations were set on soft soils. The large amount of collected data allowed comparison between observed PGA and theoretical predictions, ShakeMaps and attenuation laws, but the lack of a reference site during the 2012 recordings did not allow for estimating the amplification factor. In order to accomplish this task, in February 2013, a new 5 stations recording array acquired data at four of the 2012 network sites and at the Casaglia reference site, north of Ferrara, where a borehole Very Broad-Band station is coupled with a midperiod sensor at the surface. This borehole reference station made possible the estimation of site amplification of the 2013 array sites. The reference methods allowed an easier identification of the resonance frequency, which peaks appear sharper than what displayed by single-station methods (both H/V on ambient noise and earthquakes), and relative soil amplification. A large amount of original seismological data has been recorded in a poorly instrumented area, including significant events of the 2012 Emilia and 2013 Lunigiana sequences. The entire dataset of continuous waveforms has been made available on the OGS web based OASIS Database, from the earliest stages of the project. For the largest events strong-motion parameters were calculated and published on the OASIS database. Event time series and metadata (site monographs) are available similarly to the ITACA Database

Seismic hazard for the Trans Adriatic Pipeline (TAP). Part 2: broadband scenarios at the Fier Compressor Station (Albania)

AbstractTo ensure environmental and public safety, critical facilities require rigorous seismic hazard analysis to define seismic input for their design. We consider the case of the Trans Adriatic Pipeline (TAP), which is a pipeline that transports natural gas from the Caspian Sea to southern Italy, crossing active faults and areas characterized by high seismicity levels. For this pipeline, we develop a Probabilistic Seismic Hazard Assessment (PSHA) for the broader area, and, for the selected critical sites, we perform deterministic seismic hazard assessment (DSHA), by calculating shaking scenarios that account for the physics of the source, propagation, and site effects. This paper presents a DSHA for a compressor station located at Fier, along the Albanian coastal region. Considering the location of the most hazardous faults in the study site, revealed by the PSHA disaggregation, we model the ground motion for two different scenarios to simulate the worst-case scenario for this compressor station. We compute broadband waveforms for receivers on soft soils by applying specific transfer functions estimated from the available geotechnical data for the Fier area. The simulations reproduce the variability observed in the ground motion recorded in the near-earthquake source. The vertical ground motion is strong for receivers placed above the rupture areas and should not be ignored in seismic designs; furthermore, our vertical simulations reproduce the displacement and the static offset of the ground motion highlighted in recent studies. This observation confirms the importance of the DSHA analysis in defining the expected pipeline damage functions and permanent soil deformations

Ground motion estimation in the eastern-southern alps:from ground motion predictive equations to real-time shake maps.

2006/2007Lo scopo di questa tesi di dottorato è la stima del moto forte del suolo nell’area delle Alpi Sud-Orientali. A tal fine sono state proposte delle relazioni empiriche che stimano i parametri del moto in funzione della magnitudo, della distanza dall’epicentro e della classificazione geologica del suolo; successivamente tali relazioni sono state usate per calibrare il software ShakeMaps con il fine di generare in tempo reale le mappe di scuotimento del terreno per la regione Friuli-Venezia Giulia. Le GMPEs (Ground Motion Predictive Equations) per PGA, PGV e SA sono state calcolate nell’area delle Alpi Sud-Orientali utilizzando registrazioni del moto forte del terreno. Sono state selezionate 900 forme d’onde accelerometriche filtrate tra 0.1 Hz e 30 Hz; la distanza epicentrale varia tra 1 km a 100 km, mentre la magnitudo locale, opportunamente calibrata confrontando diversi cataloghi, varia in un intervallo relativamente ampio (3.0 <= ML <= 6.3). Sono stati testati diversi modelli di attenuazione e il miglior risultato è stato individuato utilizzando specifici criteri di valutazione derivanti da considerazioni di carattere statistico (valore di R2, uso dell’ANOVA test, analisi dei residui). I coefficienti del modello finale sono stati determinati oltre che da ML, dalla distanza epicentrale e dagli effetti dovuti al sito, anche dalla saturazione della magnitudo, dalla correlazione tra magnitudo e distanza e dagli effetti di “near-source”. I coefficienti delle GMPEs sono stati calcolati per le componenti verticali ed orizzontali (rappresentata sia con la componente maggiore sia con la somma vettoriale delle due componenti); la tecnica dell’analisi dei gruppi ha permesso di ridurre l’incertezza finale sulle relazioni empiriche. Il confronto con i risultati ottenuti precedentemente evidenzia come le relazioni ottenute in questa tesi abbiano una maggiore attenuazione a basse magnitudo e a grandi distanze; risultati analoghi sono stati ottenuti per le relazioni ricavate dai dati registrati in tutta l’Italia Settentrionale. L’evoluzione recente delle reti sismiche rende oggi disponibile una grossa mole di dati acquisiti in tempo reale, per cui risulta fattibile stimare velocemente lo scuotimento del terreno tramite mappe; il software “ShakeMap” è stato adattato alle Alpi Sud-Orientali implementato allo scopo di ottenere una stabile interfaccia con il sistema di acquisizione dati “Antelope” che garantisca l’estrazione dei parametri del moto dalle forme d’onda e la creazione delle mappe di scuotimento entro 5 minuti dall’evento sismico. Questa procedura richiede una fitta e uniforme distribuzione spaziale degli strumenti di registrazione sul territorio e una classificazione geologica del suolo fatta usando le velocita’ medie, Vs30, dei primi 30m del mezzo immediatamente sotto gli strumenti. La classificazione geologica del suolo prevede la suddivisione in tre categorie (suolo rigido, suolo addensato e suolo soffice) mentre i coefficienti di amplificazione sono stati calcolati usando le relazioni proposte da Borcherdt (1994). Le relative mappe vanno calcolate usando le GMPEs e le relazioni empiriche che legano il moto del terreno all’intensità macrosismica, basate ambedue su dati registrati nella regione alpina. Le GMPEs discusse in precedenza sono state inserite nel software “ShakeMap” per la produzione delle mappe di scuotimento in tempo reale e quasi-reale nell’Italia Nord-Orientale. Per valutare l’effetto della densità di stazioni sulle mappe di scuotimento sono stati calcolati dei sismogrammi sintetici relativi al terremoto di Bovec 2004 variando il passo di griglia e la geometria dei ricevitori. I risultati ottenuti indicano come una distribuzione fitta e uniforme di strumenti sul territorio e una scelta accurata delle dimensioni della griglia dei ricevitori siano cruciali per calibrare le mappe di scuotimento in una ben determinata area geografica. Le mappe di scuotimento del suolo sono state generate per otto terremoti avvenuti nell’area considerata negli ultimi 30 anni; inoltre per gli eventi del Friuli 1976 e Bovec 1998 è stato utilizzato il modello di faglia finita con i parametri di sorgente stimati in precedenti studi. La validazione del modello è stata fatta calcolando il misfit tra le intensità macrosismiche osservate (catalogo DBMI04) e quelle “strumentali” che sono state ottenute dai sismogrammi sintetici tramite relazioni empiriche tra moto del suolo ed intensità. L’analisi è stata fatta per i terremoti del Cansiglio (1936), del Friuli (1976) e di Bovec (1998). I sismogrammi sintetici sono stati calcolati ad una frequenza massima di 10 Hz applicando il modello della riflettività; i parametri del moto sono stati estratti dai segnali sintetici calcolati nelle attuali stazioni di registrazione e successivamente sono state generate le mappe di scuotimento. L’intensità macrosismica “strumentale” è stata ricavata applicando diverse relazioni; il minor misfit è stato ottenuto usando le relazioni proposte da Kästli and Fäh (2006) per tutti e tre i terremoti considerati, il che sembra validare il nostro modello di Shake Maps.The aim of this PhD thesis is to estimate ground motions in the South-Eastern Alps area. For this purpose we purposed empirical relationships that estimate the ground motion parameters as function of the magnitude, the epicentral distance and the soil geological characterization. Later on these relationships are used to calibrate the ShakeMaps software to generate ground motion shake maps in real time for the Friuli-Venezia Giulia region. The GMPEs (Ground Motion Predictive Equations) for PGA, PGV and SA are computed in the South-Eastern Alps area using strong motion observations. 900 accelerometric waveforms are selected and filtered between 0.1 Hz and 30 Hz; the epicentral distance varies from 1 km to 100 km, while the local magnitude, calibrated by comparison with various catalogues, varies in a relatively wide range (3.0 <= ML <= 6.3). Various attenuation models are tested and the best result is selected by the adoption of specific evaluation criteria derived from statistical considerations (R2 value, ANOVA test, residuals analysis). The coefficients of the final model are determined from ML, the epicentral distance, the site effects, the magnitude saturation, the correlation between the distance and the magnitude and the near-source effects. The coefficients of the GMPEs are computed from vertical and horizontal components (the latter represented both as the largest horizontal component and the vectorial addiction); the cluster analysis reduces the final uncertainties on the empirical relations. The comparison with the previous results evidences that the obtained relationships are characterized by a strong attenuation at low magnitudes and large distances. Similar results are obtained for the relationships derived from data recorded all over Northern Italy. The recent evolution of the seismic networks provides a large number of data, available in real time, so it is possible to quickly estimate shake maps. The “ShakeMap” software has been adapted to the South-Eastern Alps region and implemented to obtain a stable interface with the “Antelope” acquisition system in order to extract the ground motion parameters from the waveforms and the generation of the shake maps within 5 minutes from the earthquake occurrence. This procedure requires a dense and uniform spatial distribution of the recording instruments in the field and a geological classification of the soil derived from the average velocities of the S waves in the first 30m below the recording instruments (Vs30). In the geological classification the soil is divided into three classes (bedrock, stiff soil and soft soil), and the amplification coefficients are computed using the relationships proposed by Borcherdt (1994). The related maps are generated using the GMPEs and the empirical relations that predict the macroseismic intensity from the ground motion, both derived from data observed in the Alpine region. The GMPEs that are obtained in this thesis are inserted in the ShakeMap software to generate shake maps in real time or quasi real time in North-Eastern Italy. To evaluate the effects of the station coverage on the shake maps, synthetic seismograms are computed for the Bovec 2004 earthquake by varying the grid size and the network geometry. The results indicate that a dense and uniform spatial distribution in the field and a careful choice of the grid size are crucial to calibrate the shake maps in a given geographical area. The shake maps are generated for eight earthquakes occurred in the studied area in the last 30 years. Furthermore, the finite-fault model is utilized for the seismic events of the Friuli 1976 and Bovec 1998 selecting the source parameters proposed in previous studies. The model validation is done computing the misfit value between the observed macroseismic data (DBMI04 catalogue) and the “instrumental” intensities that are obtained from the synthetic seismograms using empirical relationships between the ground motion and intensity. This analysis has been done for the earthquakes of Cansiglio (1936), Friuli (1976) and Bovec (1998). The synthetic seismograms are calculated for an upper cutoff frequency of 10 Hz applying the reflectivity model. The ground motion parameters are extracted from synthetic signals computed at the presently operating seismic stations and the shake maps are generated. The macroseismic intensity is derived from various relationships; the lowest misfit is obtained using the relation proposed by Kästli and Fäh (2006) for all considered seismic events and this seem to validate our Shake Maps model.XX Ciclo197

The 2011 Mw 5.2 Lorca earthquake as a case study to investigate the ground motion variability related to the source model

Near-field recordings are very sensitive to the spatiotemporal details of the rupture process while far-field signals show the signature of the overall “point-source” earthquake mechanism. Near- and far-field recording ranges are dependent on the event magnitude and modulate the variability of the ground motion. This study investigates the ground motion and the source-related near-field variability for the 2011 Lorca earthquake, a moderate seismic event (Mw = 5.2) that caused significant localized damage in the Region of Murcia, Spain. The low-frequency content (up to 1 Hz) is simulated by the wavenumber integration method assuming four different source models obtained by inversion of geodetic or seismological data. As a first result, we estimate the variability of the ground motion. We observe that the dispersion in the peak and spectral parameters is larger at LOR, the closest station to the source, and decreases as the source distance increases (more than 50 km far from the source) where the finite-fault effects become negligible. The variability of the pseudo spectral velocity at 2 s is within the ground motion prediction equation ±1 σ, apart from the very near-source station and those stations affected by forward directivity effects. These effects are also found in high-frequency seismograms obtained by the empirical Green’s functions approach.Field work and ambient-noise analysis were partially supported by the Spanish Projects CGL2007-62454 and CGL2010-11831-E.Peer Reviewe

Site Effects in the Eastern Po Plain by Mean of Weak and Strong Earthquakes

We present the activities carried out within the S2 2012-2013 Project, funded in the frame of DPCINGV Agreement, that concerns the mid-long term Seismic Hazard Assessment in Italy on two priority areas, the Po Plain and the Southern Italy. The Po Valley, an area hitherto considered of low seismological interest, has attracted the attention of the seismological community following the events of May 20, 2012. The day after the main shock that stuck eastern Emilia in 2012, the OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale deployed a temporary seismographic network in the Ferrara area. All the investigated locations were set on soft soils. The large amount of collected data allowed comparison between observed PGA and theoretical predictions, ShakeMaps and attenuation laws, but the lack of a reference site during the 2012 recordings did not allow for estimating the amplification factor. In order to accomplish this task, in February 2013, a new 5 stations recording array acquired data at four of the 2012 network sites and at the Casaglia reference site, north of Ferrara, where a borehole Very Broad-Band station is coupled with a midperiod sensor at the surface. This borehole reference station made possible the estimation of site amplification of the 2013 array sites. The reference methods allowed an easier identification of the resonance frequency, which peaks appear sharper than what displayed by single-station methods (both H/V on ambient noise and earthquakes), and relative soil amplification. A large amount of original seismological data has been recorded in a poorly instrumented area, including significant events of the 2012 Emilia and 2013 Lunigiana sequences. The entire dataset of continuous waveforms has been made available on the OGS web based OASIS Database, from the earliest stages of the project. For the largest events strong-motion parameters were calculated and published on the OASIS database. Event time series and metadata (site monographs) are available similarly to the ITACA Database.PublishedTrieste, Italy1.1. TTC - Monitoraggio sismico del territorio nazionaleope

Second asymptomatic carotid surgery trial (ACST-2) : a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86-1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91-1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable