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Seismogenic carbonate-built normal faults: structure and deformation processes
Get PDFCarbonate-built rocks are a widely recurrent lithology often involved in most of the present seismicity occurring in densely populated areas, such as the circum-Mediterranean area (e.g., L’Aquila 2009, MW 6.1; Amatrice 2016, MW 6.5). Earthquake and fault mechanics is controlled by several properties that are distributed over a wide range of scales, spanning from the tens of kilometers to the nanoscale. In this thesis, we propose to study the architecture and the rocks of an exhumed fault zone cutting carbonates (mainly dolostones and limestones) to investigate the fault-related deformation processes that can be active during the seismic cycle. Therefore, we used a multidisciplinary approach that included (i) detailed structural field surveys (including systematic rock sample collection), (ii) construction of digital outcrop models of fault zones, (iii) rock deformation experiments (i.e., rotary-shear experiments on gouges), (iv) microstructural and mineralogical investigations of natural and experimental fault products (optical- and scanning electron microscopy, X-ray energy dispersive spectroscopy, electron backscatter diffraction, EBSD, transmission Kikuchi diffraction, TKD).
As a case study for the field investigation, we selected the seismically active fault zone outcropping within carbonates in the Central Italian Apennines, namely the Vado di Corno Fault Zone (VCFZ), exhumed from < 3 km depth. The fault zone consists of a quite complicated network of faults and fractures and of a large variety of fault rocks (foliated cataclasites, gouges, in-situ shattered rocks, sheared veins, etc.). Based on the field description of the fault and fracture network and of the distribution of fault zone rocks, we suggested that the internal structure of the VCFZ strongly resembles the buried structures associated to the seismic sequences in the Central Apennines and highlighted by high resolution hypocentral distributions obtained from seismic inversion studies (e.g., L’Aquila 2009, MW 6.1; Amatrice 2016, MW 6.5). In particular, foreshocks, main shocks and especially aftershocks re-activate (mainly as low-angle normal faults) the inherited fault structures formed from compression during the Miocene-Pliocene and the high-angle normal faults associated to the present extension occurring in the mountain belt.
Motivated by their common occurrence in the fault network of the VCFZ, we investigated the frictional behavior and microstructural evolution of gouges composed of mixtures of calcite-dolomite. We performed low- to high velocity rotary-shear friction experiments (V = 30 µms-1 – 1 ms-1) over a wide range of displacements (0.05-0.4 m), normal loads (17.5-26 MPa), deformation conditions (room-humidity vs. water-dampened) and slip histories (single slide vs. slide-hold-slide). Most of these experimental conditions reproduced the deformation conditions occurred in the VCFZ. The development of a well-defined foliation in the gouge layers occurred only in the experiments performed at slip rates of 1 ms-1 and under room-humidity conditions. Consistent with previous studies, our observations support the notion that foliated gouges and cataclasites, especially in the absence of clay minerals in the matrix, may form during seismic slip in natural carbonate-bearing faults.
Further work was focused on the investigation, especially by means of EBSD analysis, of the physical processes associated to strain accommodation both in the slip zones (composed by aggregates of nanoparticles, grain size 20-2000 nm) and in the nearby and less deformed gouge layers of the experimentally sheared calcite-dolomite mixtures. This resulted in the surprising finding of the development of a crystallographic preferred orientation (CPO) in calcite in the less deformed gouges when sheared in the purely brittle regime (i.e., max T < 30 °C). Here, the formation of a CPO was suggested to be controlled by the strong anisotropy in calcite (cleavage planes), mechanical grain rotation towards the direction of the maximum compressive stress and subsequent fracturing. Moreover, the large differential stresses (ca. 170 MPa) estimated through calcite twin paleopiezometry were interpreted as a record of the local stress (force chains) carried by grain bridges during shearing.
The analysis of the experimental slip zones of calcite-dolomite gouge mixtures slid at seismic slip rate (i.e., 1 ms-1) was carried out by the application of the novel micro-analytical technique, the TKD (this is one of the very first applications to geological materials). The main advantages of the TKD compared to standard techniques used to determine CPO in rocks, is the high spatial resolution (in our case we could use an analysis step size as small as 20 nm) and the large number of data collected, which allowed us to obtain a statistically significant CPO dataset. The presence of a very weak CPO in the nano-grains organized in a characteristic foam texture in the slip zone suggested that the main deformation mechanism during seismic slip was grain boundary sliding aided by diffusion creep.
In conclusion, based on the field, experimental and microstructural evidence reported in the thesis, earthquakes occurring in the shallow crust made of carbonate-built rocks are the result of a combination of elasto-frictional ("brittle") but especially viscous-plastic ("ductile") micro-processes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Coseismic origin of foliated cataclasites and preservation potential during the seismic cycle
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