Passive seismic investigations for landslide hazard study in rock masses

La valutazione della pericolosità da frana e la gestione del relativo rischio sono sempre stati temi ampiamente studiati nella comunità scientifica data la presenza di insediamenti popolati così come siti turistici e di interesse culturale minacciati da processi di frana. Nell’ultimo decennio, le tecniche geofisiche sono state integrate in approcci multidisciplinari per studiare processi di instabilità gravitativa e progettare sistemi di monitoraggio dedicati alla gestione di infrastrutture. Nella presente tesi di Dottorato di Ricerca, una metodologia sperimentale è stata testata in due casi di ammassi rocciosi coinvolti in fenomeni di frana per valutare quanto gli approcci di sismica passiva possano essere applicati a: i) studiare la suscettibilità da frana e produrre una zonazione della pericolosità da frana; ii) valutare la pericolosità da frana (in termini di probabilità di occorrenza); iii) gestire il rischio da frana. I processi di instabilità gravitativa avvengono a differente scala e in un diverso ambiente naturale nei due casi di studio scelti: i) una falesia rocciosa in ambiente costiero sull’isola di Malta (caso di studio Selmun); ii) un versante roccioso in area montuosa nel Centro Italia (caso di studio Peschiera). La metodologia sperimentale applicata in questa tesi di Dottorato di Ricerca impiega due differenti approcci di sismica passiva: i) analisi di rumore sismico ambientale effettuate con misure a stazione singola; ii) monitoraggio sismometrico operato attraverso sensori in configurazione di array/rete (permanente o temporanea). Il Promontorio di Selmun, situato nella costa Nord-Ovest di Malta (Mar Mediterraneo Centrale), è coinvolto in un processo di frana legato alla successione geologica dell’area: la sovrapposizione di un calcare (roccia rigida) su un’argilla plastica induce un lateral spreading associato a caduta, scivolamento e/o ribaltamento di blocchi rocciosi di varie dimensioni dal bordo della placca di calcare. L’analisi delle misure di rumore sismico ambientale ha permesso di ottenere notevoli risultati riguardo il livello di stabilità delle diverse zone instabili e, quindi, di valutare la loro differente suscettibilità da frana nel quadro di una zonazione di pericolosità da frana. In aggiunta, è stato ottenuto il principale moto proprio di un ampio blocco di roccia instabile ed è stato effettuato nel dominio del tempo uno studio preliminare di specifici parametri di misure di rumore sismico ambientale di lunga durata effettuate in zone stabili e instabili. D’altra parte, l’installazione di un array a geometria SNS ha permesso di individuare e localizzare alcuni eventi microsismici originati dal margine instabile della placca calcarea. Il Versante delle Sorgenti del Peschiera, localizzato nell’Appennino Centrale (Italia Centrale) a circa 70 km a Nord-Est di Roma, è coinvolto in un fenomeno di creep in ammasso roccioso associato ad una dissoluzione carsica profonda. Le misure di rumore sismico ambientale hanno evidenziato la diversa risposta sismica delle varie zone del versante interessato dal complesso processo di frana. Dato che il versante delle Sorgenti del Peschiera ospita un importante impianto di drenaggio di approvvigionamento di acqua per la città di Roma, una rete accelerometrica è stata installata nel 2008 ed un array SNS è stato aggiunto nel 2014. L’array SNS ha registrato centinaia di eventi microsismici originati nel versante e legati al suo processo di instabilità. Tali eventi sono stati distinti in due diversi tipi: i) rotture legate alla fratturazione dell’ammasso roccioso, con durata da 1 a qualche secondo; ii) collassi, con durata minore di 1 s e tipica forma d’onda da impatto. In questa tesi, 397 eventi (16 rotture e 381 collassi) sono stati caratterizzati con il software NanoseismicSuite in termini di magnitudo locale ML ed ipocentro. Mentre le rotture sono risultate distribuite nell’intero versante, i collassi si sono focalizzati in due diversi cluster spaziali sotto il livello di falda, ad una profondità in cui il carsismo produce cavità. I cluster sono stati trattati come due distinte sorgenti microsismogeniche ed una curva frequenza-magnitudo degli eventi è stata prodotta per ognuna, per descrivere l’attitudine a produrre eventi di diverso valore di magnitudo. È stata poi sviluppata una procedura automatizzata di analisi rapida degli eventi registrati della rete accelerometrica. Infine, una matrice di pericolosità da frana è stata implementata per entrambi i casi di studio in base alla frequenza statistica degli eventi occorsi (i valori delle misure di rumore sismico per il caso di studio di Selmun e i valori di ML dei collassi per il caso di studio del Peschiera) e la loro probabilità di eccedenza in un periodo fissato, fornendo un utile contributo nella gestione del relativo rischio da frana. In conclusione, la presente tesi di Dottorato di Ricerca evidenzia come la sismica passiva possa essere considerata un utile strumento per investigare e monitorare processi di instabilità gravitativa dato che ha consentito di raggiungere i diversi obiettivi iniziali: valutare la suscettibilità da frana, stimarne la pericolosità ed, infine, implementare uno strumento che possa contribuire alla gestione del rischio connesso.Assessment of landslide hazard and managing the related risk have always been widely studied topics in the scientific community due to the presence of populated settlements as well as tourist and cultural heritage sites threated by slope instability processes. In the last decade, geophysical techniques have been integrated in multidisciplinary approaches to study gravity-induced slope instability processes as well as to design monitoring systems devoted to infrastructure management. In the here-presented Ph.D. thesis, an experimental methodology was tested in two case studies of rock masses involved in landslide processes for evaluating as passive seismic approaches can be applied to: i) study the landslide susceptibility and produce a landslide hazard zonation; ii) assess the landslide hazard (in terms of probability of occurrence); iii) manage the landslide risk. For the two case studies, the gravity-induced slope instability processes occur at different scale and in a different natural environment: i) one rock cliff slope in coastal environment on the island of Malta (Selmun case study); ii) one rock slope in mountainous area in Central Italy (Peschiera case study). The experimental methodology applied in this work employed two passive seismic approaches: i) seismic ambient noise analysis carried out by single-station measurements; ii) seismic monitoring operated through seismic array/network (permanent or temporary) of sensors. The Selmun Promontory, located in the North Western coast of Malta (Central Mediterranean Sea), is involved in a landslide process due to the geological setting of the area: the over-position of a limestone (i.e. stiff rock) on a plastic clay induces a lateral spreading phenomenon associated to falls, slides and/or topples of different-size rock blocks from the limestone plateau edge. The seismic ambient noise measurement analysis allowed to obtain remarkable outputs in terms of stability level of the several unstable zones and, therefore, to evaluate their different landslide susceptibility in the framework of a landslide hazard zonation. In addition, the main eigenmode frequency of an unstable large rock block was obtained and a preliminary study of specific parameters was carried out in the time domain on long seismic noise measurements carried out in stable and unstable zones. On the other hand, the installation of an array having the SNS geometry allowed to detect and locate few microseismic events produced by the unstable limestone plateau edge. The Peschiera Spring Slope, located in Central Apennines (Central Italy) at about 70 km North East from Rome, is involved in a rock mass creep phenomenon associated to a deep karst dissolution. The seismic ambient noise measurements evidenced the different seismic response of the different zones of the slope involved in the complex landslide process. Since the Peschiera Spring Slope hosts an important drainage plant that provides water to the city of Rome, an accelerometric network was installed in 2008 and a nanoseismic SNS array was added in 2014. The SNS array recorded hundreds of microseismic events originated within the slope and related to its instability process. Such events were distinguished in two different types: i) failures related to rock mass fracturing, with a duration from 1 to few seconds; ii) collapses, with a duration less than 1 s and a typical waveform of impact. In this Ph.D. thesis, 397 events (i.e. 16 failures and 381 collapses) were characterised by NanoseismicSuite software in terms of local magnitude ML and hypocentre. While the failures resulted distributed into the whole slope, the collapses focused in two different spatial clusters below the groundwater level, at a depth in which karst processes produce cavities. The clusters were treated as two distinct microseismic sources and a frequency-magnitude curve of events was produced for each one, for describing the attitude to produce events having different values of magnitude. Then, an automated procedure for quickly analysing events recorded by the accelerometric network was developed. Finally, a landslide hazard matrix was implemented for the both case studies based on the statistic frequency of the occurred events (i.e. values of long seismic noise for the Selmun case study and ML values of collapses for the Peschiera case study) and their probability of exceedance in a fixed period, giving an useful contribution for managing the related landslide risk. In conclusion, the here-presented Ph.D. thesis evidences as passive seismic can be considered as a useful tool for investigating and monitoring gravity-induced slope instability processes since it allows to achieve the different initial objectives, i.e. evaluate the landslide susceptibility, assess its hazard and, finally, implement a tool for contributing to manage the related risk

Detection of nanoseismic events related to slope instabilities in the quarry district of Coreno Ausonio (Italy)

Le cave per l’estrazione di materiale roccioso rappresentano contesti in cui possono aver luogo eventi di instabilità gravitativa causati dalle continue sollecitazioni cui sono soggette le pareti produttive, principalmente connesse alle vibrazioni dovute alle esplosioni necessarie alle operazioni di disgaggio. La necessità di gestione del rischio da frana per la salvaguardia del personale impegnato nell’attività estrattiva ha portato, nel tempo, alla richiesta di attivare sistemi di monitoraggio nelle aree di coltivazione mineraria e di cava. Nel presente lavoro il monitoraggio nanosismometrico, una tecnica di geofisica passiva recentemente sviluppata per le indagini di microsismicità, è stato impiegato nel distretto di cave a cielo aperto di Coreno Ausonio (in provincia di Frosinone). Il monitoraggio nanosismometrico consente l’individuazione e la localizzazione di deboli eventi sismici, fino a magnitudo locale (ML) nell’ordine di -3, attraverso l’impiego di quattro sensori sismometrici disposti secondo una specifica geometria di array detta SNS (Seismic Navigation System). Dopo aver individuato una cava in cui erano programmate esplosioni per la volata delle pareti in roccia, nel corso del 2013 sono state organizzate 3 campagne di acquisizione durante tre giornate, pianificate in modo da monitorare l’area in un periodo compreso da qualche ora prima dell’esplosione alle 24 ore successive. Su una parete della cava non più produttiva è stato effettuato un rilevamento geologico-tecnico che ha permesso di individuare 4 principali sistemi di discontinuità e caratterizzarli in termini di giacitura, resistenza, rugosità, apertura, spaziatura e condizioni idrauliche secondo gli standard ISRM (1978). L’analisi di stabilità della parete in esame, tenuto conto della sua orientazione, ha restituito una scarsa propensione ad eventi di instabilità. Analizzando mediante il software NanoseismicSuite i dati sismometrici acquisiti è stato possibile ottenere i “supersonogrammi”, ovvero particolari spettrogrammi auto-adattanti alle variazioni del rumore sismico di fondo, dai quali sono state definite alcune caratteristiche specifiche di forma d’onda per diverse tipologie di eventi. In base ai supersonogrammi, è stato possibile individuare e localizzare 15 esplosioni, di cui 3 provenienti dalla cava di riferimento e 12 da cave adiacenti del distretto, e 27 deboli eventi di instabilità gravitativa, distinti in 23 eventi di collasso e 4 rotture legate alle fratturazione dell’ammasso roccioso. Le 3 esplosioni avvenute nella cava di riferimento, e quindi aventi coordinate di origine nota, sono state utilizzate per calibrare il modello di sottosuolo, successivamente impiegato per localizzare gli altri eventi registrati. Le rotture sono risultate originate in diverse zone del distretto estrattivo, mentre gli eventi di collasso sono stati localizzati in una specifica area e risultano essere avvenuti prevalentemente in un limitato intervallo di tempo a seguito delle 9 esplosioni registrate nella campagna del 26-27 luglio 2013. Non è stato possibile, invece, individuare eventi riconducibili ad instabilità negli orari di attività di cava a causa dell’elevato livello di rumore apportato dagli strumenti per l’estrazione e la lavorazione del materiale roccioso. Si è escluso che gli eventi di collasso fossero riconducibili direttamente all’attività di estrazione sia perché registrati al di fuori dell’orario di lavorazione delle cave sia perché, analizzando l’intera registrazione per intervalli orari, le frequenze tipiche dei macchinari di lavorazione non sono risultate energizzante. La zona di origine è risultata essere un’area nella quale sono stati rinvenuti detrito sciolto costituito da blocchi eterometrici ed una parete non in coltivazione con medesime caratteristiche delle discontinuità rispetto alla parete sulla quale era stato effettuato il rilevamento geologico-tecnico, ma con diversa orientazione. In definitiva, la fase di sperimentazione ha restituito dei risultati di indubbio interesse consentendo di mettere in evidenza alcune limitazioni del monitoraggio nanosismometrico nel contesto preso in esame, in particolare legate all’eccessiva rumorosità registrata nelle ore di attività di cava. La tecnica appare, comunque, un utile strumento di monitoraggio per i fenomeni gravitativi di debole intensità, in grado di contribuire alla gestione del rischio da frana in aree ad elevata attività antropica ed in ambienti naturalmente predisposti ad instabilità gravitative che possono interessare pareti in roccia.Nanoseismic monitoring is a passive geophysical technique used to identify and locate weak seismic events (down to local magnitudes, ML, around -3). This technique was applied in the open-pit quarry district of Coreno Ausonio (central Italy) to detect possible gravity-induced slope instabilities resulting from quarry rock blasting. After identifying an active quarry, an engineering-geological survey was carried out to characterise the jointed rock mass on an abandoned wall in front of the quarry. Four main joint sets were surveyed and their geometric and mechanical properties were measured in order to carry out stability analyses that evidenced scarce proneness to failure of the investigated wall. The analysis of seismic records obtained during three monitoring surveys, performed through the NanoseismicSuite software, made it possible to detect and characterise 15 blasts, of which 3 from the reference quarry and 12 from nearby quarries within the district, as well as 27 weak slope instability events (23 collapses and 4 failures). While failures originated from different areas of the quarry district, collapses occurred in a site characterised by an abandoned quarry having a wall more prone to gravity-induced instabilities than the one previously characterised

Rock mass characterization coupled with seismic noise measurements to analyze the unstable cliff slope of the Selmun Promontory (Malta)

In the Mediterranean area, cliff slopes represent widespread high-risk landforms as they are highly frequented touristic places often interested by landslide processes. Malta represents a significant case study as several cliffs located all around the island are involved in instability processes, as evidenced by wide block-size talus distributed all along the coast line. These diffused instabilities are related to the predisponding geological setting of Malta Island, i.e. the over-position of grained limestone on plastic clay deposits, that induces lateral spreading phenomena associated to falls and topples of different-size rock blocks and is responsible for a typical landscape with stable plateau of stiff rocks bordered by unstable cliff slopes. The ruins of Gƫajn ƪadid Tower, the first of the thirteen watchtowers built in 1658 by the Gran Master Martin de Redin, stand out in the Selmun area. Currently the safety of this important heritage site, already damaged by an earthquake on October 12th 1856, is threaten by a progressive moving of the landslide process towards the stable plateau area. During autumn 2015, a field campaign was realized to characterize the jointed rock mass. A detailed engineering-geological survey was carried out to reconstruct the geological setting and to define the mechanical properties of the rock mass. Based on the surveyed joint spatial distribution, 58 single-station noise measurements were deployed to cover both the unstable zone and the stable area. The obtained 1-hour records were analyzed in the frequency domain for associating vibrational evidences to different instability levels, i.e. deriving the presence of already isolated blocks by the local seismic response. The here presented results can be a useful contribute to begin to asses defense strategies for the Selmun Promontory, in the frame of managing the landslide risk in the study area and preserving the local historical heritage

Engineering-geological features supporting a seismic-driven multi-hazard scenario in the Lake Campotosto area (L’Aquila, Italy)

This paper aims to describe the seismic-driven multi-hazard scenario of the Lake Campotosto artificial basin (Abruzzo Region, Central Italy), and it can represent a preparatory study for a quantitative multi-hazard analysis. A comprehensive multi-hazard scenario considers all the effects that can occur following the base ground shaking, providing a holistic approach to assessing the real hazard potential and helping to improve management of disaster mitigation. The study area might be affected by a complex earthquake-induced chain of geologic hazards, such as the seismic shaking, the surface faulting of the Gorzano Mt. Fault, which is very close to one of the three dams that form the Lake Campotosto, and by the earthquake-triggered landslides of different sizes and typologies. These hazards were individually and qualitatively analyzed, using data from an engineering-geological survey and a geomechanical classification of the rock mass. With regard to the seismic shaking, a quantitative evaluation of the seismic response of the Poggio Cancelli valley, in the northern part of Lake Campotosto, was performed, highlighting different seismic amplification phenomena due to morphologic and stratigraphic features. Some insights about the possible multi-hazard approaches are also discussed

Engineering-geological modeling for supporting local seismic response studies. Insights from the 3D model of the subsoil of Rieti (Italy)

A high-resolution 3D engineering-geological model of the subsoil can be derived by integrating stratigraphic and geophysical data in order to represent reliably the geological setting, and therefore support several geological studies such as local seismic response analyses. In this study, we show how an accurate 3D engineering-geological model suggests the proper seismic response modeling approach (1D or 2D) in a peculiar and complex geological context, such as the historical city center of Rieti (Italy), selected as test site, and characterized by important lateral heterogeneities between stiff travertine and alluvial soft deposits. The proposed methodology involves three steps: (i) conceptual geological modelling, obtained from data and maps of literature; (ii) engineering-geological modeling, validated through geophysical data; and (iii) a 3D model restitution achieved by a geodatabase (built basing on the previous steps), that collects, stores, reliably represents, and integrates properly the geospatial data. The analysis of seismic ambient noise measurements specifically available for the study area allowed to infer the shear wave velocity value for each lithotecnical unit and to retrieve some additional stratigraphies. These synthetic log stratigraphies allowed to improve the detail of the geodatabase and therefore a more accurate 3D geological model. Such a reliable engineering-geological model of the subsoil is required to perform a site-specific seismic response characterization which is a fundamental tool in the framework of seismic risk management

Evaluating characteristics of an active coastal spreading area combining geophysical data with satellite, aerial, and unmanned aerial vehicles images

The northern region of the Maltese archipelago is experiencing lateral spreading landslide processes. This region is characterized by cliffs with a hard coralline limestone outcropping layer sitting on a thick layer of clay. Such a geological configuration causes coastal instability that results in lateral spreading which predispose to rockfalls and topplings all over the cliff slopes. The aim of this research was to develop a methodology for evaluating cliff erosion/retreat using the integration of geomatics and geophysical techniques. Starting from a 3D digital model of the Selmun promontory, generated by unmanned aerial vehicle (UAV) photogrammetry, it was possible to map the fractures and conduct geophysical measurements such as electrical resistivity tomography and ground penetrating radar for the identification and mapping of vertical fractures affecting the hard coralline limestone plateau, and to create a 3D geological model of the study area. In addition to this, high-accuracy orthophotos from UAV that were captured between 1957 and 2021 were georeferenced into a GIS and compared to aerial and satellite images. The movement and evolution of boulders and cracks in rocks were then vectorized to highlight, track and quantify the phenomenon through time. The results were used to derive a qualitative assessment of the coastal variations in the geometric properties of the exposed discontinuity surfaces to evaluate the volumes and the stop points of the observed rockfalls. The outcomes of this research were finally imported in a GIS which offers an easy approach for the collection and processing of coastal monitoring data. In principle, such a system could help local authorities to address social, economic and environmental issues of pressing importance as well as facilitate effective planning in view of a risk mitigation strategy

A microbial fuel cell measuring system for corrosion assessment

Microbiologically Influenced Corrosion (MIC) is a huge problem for components put into service in unclean industrial systems and marine environment. For this reason, developing new and more effective testing methodologies for the study of this form of corrosion is surely an important need. An innovative approach consists in the use of Microbial Fuel Cells as environment in which to carry out tests to assess the resistance of a specific material to MIC. This new methodology will be described, presenting possible studies that can be performed and information that can be gained. Moreover, a new measuring setup has been developed, which enables researchers to get more specific information about the test, assessing all current flows inside the Fuel Cell. Two different materials (low carbon steel and stainless steel) have been used to carry out different experiments and validate the employed methodology. Results obtained with this measuring system have been then compared with those of a simpler setup, showing the effectiveness of this apparatus in studying MIC

Vidas profissionais de dois Professores de Educação Física e Pesquisadores brasileiros: encontros e desencontros com as práticas colaborativas

The purpose of this article is to explore the collaborative practices and socialisation experiences of two Physical Education (PE) teachers and researchers in Brazil. This qualitative and collaborative case study had as participants two Brazilian professionals working in schools and universities and two critical friends. Critical incidents related to collaborative practices were identified through charts and photo-elicitation in four online meetings. The results were analyzed in light of the theory of teacher socialisation and revealed that: (a) collaborative practices can be considered as complex and dialogical processes that provide different experiences (positive and negative) in life and career; and (b) socialisation as a non-linear process that can be enhanced with research and collaboration. The findings contribute to broadening the understanding of collaborative practices in support of sustainable and meaningful careers.El objetivo de este artículo es explorar las prácticas colaborativas y las experiencias en la socialización de dos profesores e investigadores de Educación Física (EF) en Brasil. Este estudio de caso cualitativo y colaborativo tuvo como participantes a dos profesionales brasileños que actúan en escuelas y universidades y dos amigos críticos. Se identificaron incidentes críticos relacionados con las prácticas colaborativas a través de gráficos y fotoelicitación, en cuatro encuentros online. Los resultados se analizaron a la luz de la teoría de la socialización docente y revelaron que: (a) las prácticas colaborativas pueden ser consideradas como procesos complejos y dialógicos que proporcionan diferentes experiencias (positivas y negativas) en la vida y en la carrera; y (b) la socialización como un proceso no lineal que se puede mejorar con investigación y colaboración. Los hallazgos contribuyen a ampliar la comprensión de las prácticas colaborativas en apoyo a carreras sostenibles y significativas.O objetivo deste artigo é explorar as práticas colaborativas e as experiências na socialização de dois professores e pesquisadores de Educação Física (EF) no Brasil. Este estudo de caso qualitativo e colaborativo teve como participantes dois profissionais brasileiros que atuam em escolas e em universidades e dois amigos críticos. Foram identificados incidentes críticos relacionados às práticas colaborativas por meio de gráficos e foto-elicitação, em quatro encontros online. Os resultados foram analisados à luz da teoria da socialização docente e revelaram que: (a) as práticas colaborativas podem ser consideradas como processos complexos e dialógicos que proporcionam diferentes experiências (positivas e negativas) na vida e na carreira; e (b) socialização como um processo não linear que pode ser melhorado com pesquisa e colaboração. Os achados contribuem para ampliar a compreensão das práticas colaborativas em apoio a carreiras sustentáveis ​​e significativas

A Novel Approach for Microbial Corrosion Assessment

Materials corrosion in the presence of bacteria [microbiologically influenced corrosion, (MIC)] is an important issue for components deployed in industrial applications and marine environments, where unexpected and fast degradation is often observed. For these reasons, finding new testing methodologies to assess the behavior of different materials in these conditions is a topic of clear interest. This paper describes a new approach based on the use of microbial fuel cells, which are exploited to have known and controlled conditions during the test. The sample is immersed in an environment where the presence and activity of electroactive bacteria are easily monitored measuring the currents flowing between the electrodes of the cell. Then, after connecting the sample of the material under study, reactions occurring on its surface can be monitored and its corrosion resistance can be assessed. This novel methodology is simple, easy to deploy, and can be proposed to assess microbial corrosion resistance of metals and alloys, monitoring, at the same time, the biofilm grown on the metals surface