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Computation of run-up heights for landslide-generated tsunami. An attempt of hazard assessment in the North Sicily continental margin
No full textThe North Sicily continental margin is a very active region located in a transitional area between the Sicilian-
Maghrebian Chain to the south and the southern Tyrrhenian Sea to the north. Strong seismicity, active tectonics and
volcanism, fluid escape, high sediment supply and widespread mass movements exposed this region to marine geohazards,
with a potential for tsunami generation (e.g. Messina 1908, Stromboli 2004 events).
In recent years, high resolution swath mapping and high resolution to high penetration seismic reflection profiles
have been collected during several oceanographic cruises, in the frame of the MaGIC and CARG projects.
Morphobatymetric and geoseismic analysis evidenced the main hazard elements and allowed the production of risk
maps.
Available data revealed that one of the most common mechanisms associated with marine geo-hazards is due to
submarine mass failure processes, genetically linked to other processes active in this margin (canyon, gas venting,
volcanism, tectonic structures, volcanoes, high sedimentation rate).
With the aim to assess the risks linked to landslide-generated anomalous waves we selected two different sectors of
the North Sicily continental margin, located in the western (Gulf of Palermo) and eastern (offshore Patti) coasts. These
area were selected based on their morphologic, stratigraphic and tectonic setting and for the large amount of
morphostructural elements.
The working flow developed through different steps as follows:
• identification and mapping of the main morphobathymetric elements affecting unstable areas;
• characterization and morphometric analysis of landslide scars (ten Brink et al., 2006) selected on the
base of their hazard potenzial;
• computation of parameters (wavelenght, velocity, amplitude) of landslide-generated anomalous waves
(Rahiman and Pettinga, 2006);
• modelling tsunami runup expected by the largest failure volume, breaking on the Sicily coastline,
based on Green law relations and solution of the Boussinesq equations (Choi et al., 2006).
In detail, we obtained values of maximum run-up of 6.6-9.1 m for the Gulf of Palermo and 6.3-13.3 m for the Patti
offshore. However the obtained values appear to be overvalued because the model foresees a precautionary scenario.
Moreover the next step will be the assessment of inundation, taking into account the morphologic features of the coastal
area and the roughness, land-use and urbanization of the affected areas, concerning a wider concept of risk assessment
Seismotectonics in the North-Western Sicily Continental Margin: implications for Geohazard assessment
Full text linkActive processes in the Northern Sicily Continental Margin (NSCM) have been analysed to produce a seismotectonic map, in order to obtain a useful tool for the assessment of the seismic hazard of the sea-land region.
The seismotectonic map is composed of overlapping layers that represent the distribution of different features, such as lithostratigraphy, tectonic elements, seismicity, heat flow, gravimetry, magnetometry, Moho depth, horizontal and vertical movements, submarine landslides, fluid emissions, outlining the mutual relationship and the active structures.
The NSCM is suitable to test this approach because it’s located in a transitional area between the Sicilian-Maghrebian chain to the south and the Tyrrhenian back-arc basin to the north. Along this transect the Moho depth ranges from about 10 km, in the Marsili bathyal plain, to about 40 km, towards the northern Sicily coast. The Bouguer anomalies change from 180 mGal in the Tyrrhenian region to negative anomalies in central Sicily (-100 mGal), while positive magnetic anomalies characterize the volcanic edifices, both submerged and buried. The heat flow values are high in the Tyrrhenian Sea (200 mW/m-2), decreasing (30-40 mW/m-2) towards the stable sector of the foreland area (Iblean plateau in SE Sicily).
At a regional scale, in the NSCM we distinguished different seismogenetic volumes, both shallow and deep. The deep seismicity, relative to the Ionian subduction, is prevailing in the eastern margin, but the shallow events are the result of the brittle deformation of the Maghrebian chain. In the western sector, shallow hypocentres occur along an E-W belt, with focal mechanisms coherent with a NW-SE compression. To the East seismicity is linked to NW-SE trending extensional to right-lateral transcurrent fault systems.
During the last 125 ky tectonic activity is evidenced by vertical movements, decreasing from E to W; moreover, while the continental sectors are raised, offshore areas are subsiding, suggesting the occurrence of vertical differential movements. The GPS values document the active deformation with differential movements of individual blocks northward-directed, in agreement with the shallow seismicity, as well as the convergence between Sicily and Sardinia, with values of about 2-6 mm/y.
The first step of this research produced the detailed seismotectonic map between the Castellammare and Palermo gulfs, including both the emerged and marine areas. In this sector we defined two seismogenetic volumes, produced by a NW-SE oriented compressional stress field, and defining an intraplate shallow seismogenetic zone. Though these results are only preliminary, we are developing a scientific product that can provide useful information in terms of seismic hazard in a complex region that includes both continental and marine sectors. Therefore, it could represent an important tool for monitoring the potentially seismogenic structures and assessing geohazards in marine and coastal environment
Sismotettonica del Margine Continentale della Sicilia nord-occidentale: implicazioni per la valutazione del geohazard
Full text linkI processi tettonici attivi nel margine continentale della Sicilia settentrionale (MCSS) sono stati analizzati per la realizzazione della carta sismotettonica, al fine di ottenere uno strumento utile per la valutazione della pericolosità sismica della regione.
La carta sismotettonica è realizzata attraverso la sovrapposizione di layer che rappresentano la distribuzione di tematismi, quali litostratigrafia, tettonica, sismicità, flussi di calore, gravimetria, magnetometria, profondità della Moho, movimenti orizzontali e verticali, frane, fuoriuscite di fluidi, evidenziando la relazione tra questi e le strutture attive.
Il MCSS si trova in una zona di transizione tra la catena siciliano-maghrebide a sud e il bacino tirrenico di retro-arco a nord, dove la profondità della Moho varia da circa 10 km nella piana del Marsili, a circa 40 km verso le coste nord siciliane. Le anomalie di Bouguer passano da valori di 180 mGal nel Tirreno ad anomalie negative nella Sicilia centrale (-100 mGal), mentre anomalie magnetiche positive caratterizzano gli edifici vulcanici, anche sommersi o sepolti. I valori di flusso di calore sono elevati nel Tirreno (200 mW/m-2) e diminuiscono (30-40 mW/ m-2) verso l’avampaese.
Nel MCSS si possono distinguere diversi volumi sismogenetici, sia superficiali che profondi. La sismicità profonda, relativa alla subduzione ionica, è presente nella parte orientale del margine, quella superficiale è invece il risultato della deformazione fragile della catena maghrebide. Nel settore occidentale gli eventi superficiali si verificano lungo una fascia a direzione E-W, con meccanismi focali in accordo con una deformazione compressiva NW-SE. Verso Est la sismicità è legata a sistemi di faglie distensive e trascorrenti destre NW-SE. Durante gli ultimi 125 ky l’attività tettonica è evidenziata da movimenti verticali, che mostrano una diminuzione da E a W; inoltre, mentre i settori continentali sono sollevati, le aree offshore sono in subsidenza, suggerendo l'esistenza di movimenti verticali differenziali. I valori di GPS documentano la deformazione attiva con movimenti differenziali di singoli blocchi verso i quadranti settentrionali, in accordo con la sismicità superficiale, e la convergenza tra Sicilia e Sardegna, con valori di circa 2-6 mm/anno.
Il primo step della ricerca ha previsto la realizzazione della carta sismotettonica del settore compreso tra i golfi di Castellammare e Palermo, comprendendo sia la parte emersa che sommersa. In questo settore ricadono due volumi sismogenetici, prodotti dal campo di stress compressivo orientato NW-SE. Per quanto i risultati siano preliminari, è in corso di elaborazione un prodotto scientifico in grado di fornire informazioni utili in termini di pericolosità sismica in un settore che comprende sia aree continentali che marine. In questo senso, può rappresentare uno strumento importante in termini di monitoraggio delle strutture potenzialmente sismogenetiche e dei geohazard in ambiente marino e costiero
Analisi comparata di metodi di calcolo del run-up per tsunami generati da frana. Casi di studio nel Margine Continentale della Sicilia Settentrionale
Full text linkIl margine continentale della Sicilia settentrionale è caratterizzato dalla presenza di pericolosità geologiche
(sismicità, vulcanismo, risalita di fluidi e movimenti di massa) che espongono questa regione a rischi geologici
marini, con potenziale di generazione di tsunami.
Gli tsunami sono onde anomale solitarie legate a movimenti verticali improvvisi dei fondali. Le caratteristiche
principali di un’onda anomala sono rappresentate dall’elevata lunghezza d'onda e da un’altezza che varia
notevolmente durante la propagazione.
L'obiettivo di questo lavoro è quello di calcolare il run-up associato a tsunami generati da frane. Nel nostro
caso sono stati presi in esame due settori della costa settentrionale siciliana, Golfo di Palermo e Golfo di Patti,
dove l’analisi di dati geofisici ad alta risoluzione (morfobatimetrici e sismici) mette in evidenza tra gli elementi
morfologici numerose frane sottomarine.
In letteratura per calcolare il valore di run-up si usano diversi algoritmi che generalmente hanno come
incognita l’ampiezza dell’onda in corrispondenza del punto sorgente. Partendo dalle caratteristiche
morfometriche della frana, l’ampiezza viene calcolata attraverso la formula proposta da McAdoo (2004).
In questo lavoro, sono state parametrizzate tutte le frane riconosciute nell’area e di esse sono stati calcolati
i valori di run-up di eventuali onde anomale attraverso vari algoritmi (Gedik et al., 2005; Federici et al., 2006;
Xi Zhao et al., 2010; Bryant 2008). Queste formule impongono alcune condizioni, che risultano essere
“cautelative” sotto il profilo della pericolosità:
1. l’altezza d’onda non subisce variazioni legate alla morfologia della costa;
2. l’energia persa durante la propagazione è zero;
3. l'energia si trasforma istantaneamente da cinetica a potenziale durante la propagazione.
Successivamente è stato calcolato il run-up di frane storiche che hanno effettivamente generato uno
tsunami, ed i risultati ottenuti attraverso l’applicazione di queste formule sono stati confrontati con i valori
reali. Ciò ha consentito di evidenziare gli algoritmi che descrivono al meglio i fenomeni storici, fornendo uno
strumento per orientare la scelta della formula più idonea.
Infine, dall’analisi grafica della relazione tra valori di run-up ed ampiezza d’onda in prossimità del punto
sorgente è stata estrapolata una funzione utile per calcolare il run-up in maniera speditiva
Active north-vergent thrusting in the northern Sicily continental margin in the frame of the quaternary evolution of the Sicilian collisional system
No full textA three-stage evolution has characterized the Sicilian Fold and Thrust Belt (SFTB) during the last 15 My: two main thin-skinned shortening events involving mainly Meso-Cenozoic carbonate units, followed by thick-skinned thrusting involving Plio-Pleistocene deposits in the frontal area as well as the crystalline basement in the inner and deeper sector of the chain. We investigated the northern Sicily continental margin, by using differently-penetrative seismic reflection data and new field surveys, which revealed, both offshore and onshore, north-vergent compressional structures that affected the tectonic edifice during Quaternary time. These structures, correlated with the kinematic setting pointed out by seismicity and GPS measurements, could disclose an important change in distribution and orientation of deformation in the frame of the Africa-Europe convergence. Our hypothesis is that the most recent tectonic processes in the northern Sicily continental margin are representative of a jump of the deformation from the frontal area of the SFTB in the Sicily Channel to the inner sector in the Southern Tyrrhenian Sea. This study is in agreement with recent interpretations about a change in the subduction polarity in the central Mediterranean orogenic system, as a consequence of the ongoing collision of the African promontory with the thinned continental to oceanic sectors (Algerian and Tyrrhenian basins) of the European plate. The seismic activity associated with the north-vergent thrust could have implication for the assessment of the seismic risk in the Central Mediterranean and understanding of active structures in marine areas that could be responsible for tsunami hazard
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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