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Structure, evolution and deformation mechanisms of crustal-scale seismogenic faults (Bolfin Fault Zone, Northern Chile)
Full text linkI terremoti sono tra i più letali disastri naturali causando più di 50000 vittime all'anno e decine di miliardi di euro di danni nel XXI secolo. Tra i molti fattori che controllano la meccanica dei terremoti, l'architettura tridimensionale (cioè la geometria, topologia e distribuzione spaziale del network di faglie e il danneggiamento associato alle faglie) dei sistemi di faglia e i fluidi contribuiscono a controllare il comportamento sismico vs. asismico delle faglie. Tuttavia, le faglie crostali (cioè in grado di generare terremoti >6.0 MW) sono difficilmente ben esposte sulla superficie terrestre. Per questo motivo, conosciamo poco la loro architettura e la loro evoluzione spazio-temporale. In questa tesi, ho studiato la Faglia Bolfin (o Bolfin Fault Zone, BFZ). E’ una faglia trascorrente a scala crostale del Cretaceo Inferiore eccezionalmente esposta per oltre 40 km nel deserto di Atacama (Cile settentrionale). Nello specifico, ho studiato (i) l'evoluzione strutturale, e (ii) la variabilità architetturale della faglia lungo strike, e (ii) le condizioni deformative e ambientali (compresa l'interazione fluido-roccia) durante l'attività della faglia.
La BFZ è composta di tre segmenti principali, ha una geometria sinuosa a scala crostale che taglia plutoni dioritici e tonalitici-granodioritici del Giurassico-Cretaceo Inferiore. La antica sismicità (125-118 Ma), documentata da pseudotachiliti, è avvenuta a 5-7 km di profondità e ≤ 300 °C in un ambiente ricco di fluidi come documentato da un'estesa alterazione propillitica e vene di epidoto-clorite(-quarzo-calcite). La geometria sinuosa a scala crostale della BFZ è il risultato di (i) sfruttamento di anisotropie geometriche (cioè foliazione magmatica di plutoni e sciami di dicchi) durante la nucleazione della faglia e (ii) connessione di questi segmenti di faglia vincolati dalle anisotrope, attraverso faglie di tipo splay, durante la crescita della faglia. Nel complesso, l'architettura della BFZ è costituita da nuclei di faglia multipli e alterati idrotermalmente, che presentano pseudotachiliti, inclusi all'interno di una zona di danneggiamento alterata idrotermalmente, che include network di vene-faglie mineralizzate a epidoto e brecce dilatanti che si trovano in corrispondenza di intersezioni e connessioni di faglia. Comparando la BFZ con faglie crostali sismicamente attive, il network di faglie a pseudotachiliti e l’esteso network di vene-faglie mineralizzate a epidoti sono associate rispettivamente a terremoti mainshock-aftershock (i) e sciami sismici. La geochimica degli isotopi dell'idrogeno indica che le pseudotachiliti si sono formate in un ambiente tamponato dalle rocce incassanti, caratterizzato da una circolazione limitata e locale di fluido. Invece, la successiva sismicità guidata da a fluidi attestata dal network di vene-faglie idrotermali è stata controllata dall'ingresso di fluidi superficiali in un sistema idrotermale più maturo e collegato idraulicamente. In conclusione, la BFZ rappresenta un analogo esumato del volume sismogenico crostale, in grado di aver generato terremoti mainshock-aftershock, e successivi sciami sismici. La transizione del tipo di attività sismica era controllata dall'architettura della faglia e dall'ambiente geochimico.Earthquakes are among the deadliest natural disasters causing, causalities for >50000 people for year and tens of billions of euros of damage in the XXI century. Among the many factors controlling earthquake mechanics, the three-dimensional architecture (i.e., geometry, topology and spatial distribution of fault networks and fault-related damage) of fault systems and fluids contribute to the seismic vs. aseismic behavior of faults. However, crustal faults (i.e., capable to generate >6.0 MW earthquakes) are hardly well exposed at the Earth’s surface. In turn, little is known about their architecture and spatio-temporal evolution. In this thesis, I studied the Bolfin Fault Zone (BFZ), a crustal-scale Early Cretaceous strike-slip fault exceptionally exposed over more than 40 km in the Atacama Desert (Northern Chile). Specifically, I focused on the (i) structural evolution and along-strike architectural variability of the fault, and (ii) the deformation and ambient conditions (including fluid-rock interaction) during fault activity.
The BFZ is arranged into three main segments and has a sinuous crustal-scale geometry cutting through Jurassic to Early Cretaceous diorite and tonalite-granodiorite plutons. Ancient (125-118 Ma) seismic faulting, documented by pseudotachylytes, occurred at 5-7 km depth and ≤ 300 °C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite(-quartz-calcite) veining. The sinuous crustal-scale geometry of the BFZ resulted from (i) exploitation of precursory geometrical anisotropies (i.e., magmatic foliation of plutons and dyke swarms) during fault nucleation and (ii) hard linkage of these anisotropy-pinned fault segments, through splay faults, during fault growth. Overall, the BFZ architecture consists of hydrothermally altered multiple fault core strands, presenting pseudotachylytes, enveloped within a hydrothermally altered damage zone, which includes clusters of epidote-rich fault-vein networks and dilational breccias occurring at fault intersections and linkages. By comparison with active crustal fault zones, the pseudotachylyte-bearing fault network and extensive epidote-rich fault-vein networks were associated with mainshock-aftershocks and swarm-like earthquake sequences, respectively. Hydrogen isotope geochemistry indicates that pseudotachylytes formed in a rock-buffered environment, characterized by limited and local fluid circulation. Instead, the later fluid-driven seismicity attested by the hydrothermal fault-vein network was controlled by the ingression of superficial fluids in a more mature, hydraulically connected, upper-crustal hydrothermal system. In conclusion, the BFZ represents an exhumed analogue of crustal seismogenic volume, capable to have generated mainshock-aftershocks and later swarm-like earthquake sequences. The transition in the type of seismic activity was controlled by the fault architecture and the geochemical environment
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
Formation of cockade breccias in extensional brittle faults (Col de Teghime, Alpine Corsica)
Full text linkIt is well-known that fluid migration in the Earth’s upper crust is strongly controlled by the structure of fault zones. Importantly, fluid migration and pore fluid pressure variations in fault networks control the nucleation and evolution of earthquake sequences.
Vein filling in fault zones is one of the most impressive geological signatures of the interaction between fluids and fault zone rocks. A relatively common fault vein filling fabric is the spectacular cockade breccia, consisting of fragments of wall- and fault rocks rimmed and sealed by concentric layers of fluid-precipitated minerals. Consequently, the formation of cockade breccia requires rock fragmentation and cementation in the presence of fluids under particular physical and chemical conditions that may occur during different phases of the seismic cycle.
This thesis discusses the structure and the mechanism of formation of
cockade breccia hosted in the slipping zones of the Miocene in age extensional
brittle faults that cut quartzites and impure dolomitic marbles of the Schistes
Lustrés Complex from Alpine Corsica (France). Original structural geology
field surveys and detailed microstructural (optical cathodoluminescence and
scanning electron microscopy; micro-tomography; image analysis) and mineralogical/geochemical (micro-Raman spectroscopy, X-ray powder diffraction,
Energy-dispersive X-ray spectroscopy) investigations of the fault rocks indicated
that: (a) core clasts of the cockades derive from the wall rocks, have rounded shape and are well-sorted with the fraction finer < 310 µm in diameter almost
completely absent; (b) the core clasts of the cockades are suspended (i.e., do not touch each other) in the slipping zones; (c) in some slipping zones, the core clasts are arranged in inverse grading; (d) the concentric layers (systematically four in total) rimming the clasts of the
cockades have strong mineralogical zoning consisting of alternate/rhythmic
precipitation of saddle dolomite, Mg-calcite and Fe- and Ti-oxides/hydroxides; (e) cockade-breccia are cut but also kinematically associated with veins made
of ultrafine (size < 200 µm) wall rock clasts cemented by the same mineral
assemblage of the rims of the cockades; (f) the cockade breccia are cut by dolomite-bearing veins and partly sealed by late precipitation of calcite.
The above findings allowed me to propose the following model for the formation
of the cockade-bearing faults. The model links the formation of the cockade
microstructures numbered (a) to (f) to different phases of the seismic cycle:
(1) co-seismic fragmentation of the wall rocks (a) in presence of CO2- and
Fe-rich fluids which promoted also the rounding of the clasts (abrasion and
chemical wear); (2) co-seismic fluidization of the rock fragments associated
to fluid pulses migrating in the fault zone. Fluidization resulted in elutriation
of the fine particles, which were deposited in distal veins (e), and formation of
a residual very porous and well-sorted clast assemblage (a) which will make the
core of the cockades. Inverse grading (c) and rounded shape (a) of the cores
resulted by shaking (Brazil-Nut Effect) and co-seismic shearing of the clasts;
(3) post-seismic to interseismic cementation by deposition of concentric
carbonate-rich rims (d) around the core clasts of the cockades. Rim deposition
was probably due to slow (years to centuries?) mineral pressure growth processes
associated to the ingression of fluids with variable composition in the porous
clast assemblage. Pressure growth resulted in the progressive lift of the clasts
and in their "suspension" in the cockade assemblage (b). The precipitation
of saddle dolomite and the late and partial sealing of the cockade breccia by
calcite cement (f) suggest that the cockade breccia formed at shallow depths in
the crust (< 2 km).
Based on this conceptual model, cockade breccias are particular fault rock
assemblages which record the passage of seismic ruptures in the presence of
pressurized migrating fluids. Given the scarcity in the current literature of
fault rock assemblages possibly associated to seismic faulting, the results of
this study may allow us a better comprehension of earthquake-related processes
at shallow crustal depths and find application in seismic hazard studie
Formation of cockade breccias in extensional brittle faults (Col de Teghime, Alpine Corsica)
Full text linkIt is well-known that fluid migration in the Earth’s upper crust is strongly controlled by the structure of fault zones. Importantly, fluid migration and pore fluid pressure variations in fault networks control the nucleation and evolution of earthquake sequences.
Vein filling in fault zones is one of the most impressive geological signatures of the interaction between fluids and fault zone rocks. A relatively common fault vein filling fabric is the spectacular cockade breccia, consisting of fragments of wall- and fault rocks rimmed and sealed by concentric layers of fluid-precipitated minerals. Consequently, the formation of cockade breccia requires rock fragmentation and cementation in the presence of fluids under particular physical and chemical conditions that may occur during different phases of the seismic cycle.
This thesis discusses the structure and the mechanism of formation of
cockade breccia hosted in the slipping zones of the Miocene in age extensional
brittle faults that cut quartzites and impure dolomitic marbles of the Schistes
Lustrés Complex from Alpine Corsica (France). Original structural geology
field surveys and detailed microstructural (optical cathodoluminescence and
scanning electron microscopy; micro-tomography; image analysis) and mineralogical/geochemical (micro-Raman spectroscopy, X-ray powder diffraction,
Energy-dispersive X-ray spectroscopy) investigations of the fault rocks indicated
that: (a) core clasts of the cockades derive from the wall rocks, have rounded shape and are well-sorted with the fraction finer < 310 μm in diameter almost
completely absent; (b) the core clasts of the cockades are suspended (i.e., do not touch each other) in the slipping zones; (c) in some slipping zones, the core clasts are arranged in inverse grading; (d) the concentric layers (systematically four in total) rimming the clasts of the
cockades have strong mineralogical zoning consisting of alternate/rhythmic
precipitation of saddle dolomite, Mg-calcite and Fe- and Ti-oxides/hydroxides; (e) cockade-breccia are cut but also kinematically associated with veins made
of ultrafine (size < 200 μm) wall rock clasts cemented by the same mineral
assemblage of the rims of the cockades; (f) the cockade breccia are cut by dolomite-bearing veins and partly sealed by late precipitation of calcite.
The above findings allowed me to propose the following model for the formation
of the cockade-bearing faults. The model links the formation of the cockade
microstructures numbered (a) to (f) to different phases of the seismic cycle:
(1) co-seismic fragmentation of the wall rocks (a) in presence of CO2- and
Fe-rich fluids which promoted also the rounding of the clasts (abrasion and
chemical wear); (2) co-seismic fluidization of the rock fragments associated
to fluid pulses migrating in the fault zone. Fluidization resulted in elutriation
of the fine particles, which were deposited in distal veins (e), and formation of
a residual very porous and well-sorted clast assemblage (a) which will make the
core of the cockades. Inverse grading (c) and rounded shape (a) of the cores
resulted by shaking (Brazil-Nut Effect) and co-seismic shearing of the clasts;
(3) post-seismic to interseismic cementation by deposition of concentric
carbonate-rich rims (d) around the core clasts of the cockades. Rim deposition
was probably due to slow (years to centuries?) mineral pressure growth processes
associated to the ingression of fluids with variable composition in the porous
clast assemblage. Pressure growth resulted in the progressive lift of the clasts
and in their "suspension" in the cockade assemblage (b). The precipitation
of saddle dolomite and the late and partial sealing of the cockade breccia by
calcite cement (f) suggest that the cockade breccia formed at shallow depths in
the crust (< 2 km).
Based on this conceptual model, cockade breccias are particular fault rock
assemblages which record the passage of seismic ruptures in the presence of
pressurized migrating fluids. Given the scarcity in the current literature of
fault rock assemblages possibly associated to seismic faulting, the results of
this study may allow us a better comprehension of earthquake-related processes
at shallow crustal depths and find application in seismic hazard studiesope
Studio geologico- strutturale della frana di Alleghe (Rocca Petore, BL) Geological and structural study of the Alleghe rockslide (Rocca Pietore BL)
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Structural evolution of a crustal-scale seismogenic fault in a magmatic arc: The Bolfin Fault Zone (Atacama Fault System)
No full textAttitude and kinematics of the different structural elements (magmatic foliations, dykes, joints, faults and ductile shear zones) from the Bolfin Fault Zone and the Cerro Cristales Shear Zone (Atacama Fault System, Chile
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