1,721,014 research outputs found
Modeling fluid flow in fault zones: two different-scale cases from Majella Mountain and East Pacific Rise
Full text linkA quantitative assessment of how rock discontinuities (i.e., fractures and faults) control the migration of geofluids is critical in several areas of geological and environmental sciences.
In this project I concentrated my attention to two problems at the extreme range of the spectrum of fluids properties, in two different geological settings: the flow of CO2 from a natural reservoir and the melt migration in mid-ocean transform fracture zones.
The specific targets of my studies were:
-a fault zone exposed in the Roman Valley Quarry (Lettomanoppello, Italy);
-the fracture zone of the Siqueiros Transform Fault (East Pacific Rise);
The thesis is structured starting from a general overview of the two study cases and then describing in detail the methods used and the results achieved for each scenario.
To model the migration of CO2 in a fault zone, I created a new pipeline that starts from the field data and then uses open source software and new developed codes to model the fluid flow in a fault zone considering all its components: core and damage zones.
I selected the Roman Valley Quarry as study site because of the great exposure of the inner structure of two oblique slip normal faults. Besides, the massive presence of fluid migration in the form of tar in the fracture systems makes this site a good natural analogue for studies of fluid flow in fractured media.
The work on the fault zone of Roman Valley Quarry can be divided in three main parts:
1. Collection of quantitative information on the fractures/fault distribution;
2. Application of state-of-art modelling techniques to infer the hydraulic properties of the fractured reservoir from field data;
3. Numerical modeling of flow of CO2 in the fractured reservoir;
I modeled the data collected in the field to infer the hydraulic properties of the fractured reservoir (i.e. the Bolognano Formation). I employed a hybrid numerical technique, modeling the damage zones as a fractured medium and the core as a continuum medium. This allowed me to:
1. characterize the hydraulic differences observed in the field between the southern part and the northern part of the fault;
2. characterize the hydraulic parameters of the footwall and hangingwall damage zones;
3. use these values to model the fluid flow in the whole fault zone, coupling damage zones and core.
I built Discrete Fracture Networks (DFN) models using both commercial (Move®) and open source software (dfnWorks, developed by Los Alamos National Laboratory). Move® has been used to model the hydraulic differences found in the field between the northern and southern sector of the fault. dfnWorks has been used to infer the hydraulic parameters of the fracture systems of the damage zones of the fault. These parameters have then been used to upscale the properties of the fractures to an equivalent continuum medium, in order to simulate the fluid flow in the entire fault zone, coupling the core and the damage zones.
The numerical model of CO2 flow in the fault zone was developed using the open source software PFLOTRAN. To better reproduce a real-life case study, I simulated the injection of CO2 into the footwall of the Roman Valley Quarry fault. Hydrostatic initial conditions have been imposed, according to the pressure distribution in the domain. An injection mass rate has been imposed at the location of the well to simulate the injection of CO2. First, I run a number of simulations to test the workflow and verify the consistency of the numerical results. Once I obtained a stable numerical framework, I run several numerical experiments.
Results from numerical experiments show that the distribution of the CO2 in the domain appears mainly controlled by the permeability distribution in the damage zone of the fault. The CO2 in fact accumulates in the high permeability fault footwall, where the injection happens and reaches the maximum values of the pressure and saturation close to the core of the fault, that is characterized by a low permeability. Although developed and calibrated for the specific site of the Roman Valley Quarry fault, the methodology developed in this study can be extended to different geological contests.
Although not originally part of my PhD proposal, the involvement on the Off-Axis Seamounts Investigations at Siqueiros (OASIS) project was a unique opportunity to learn how to collect, process and employ geophysical data to characterize and model fluid flow (in this case, magmatic melts) near a fault zone.
The OASIS (Off-Axis Seamount Investigations at Siqueiros) expedition is a multidisciplinary effort to systematically investigate the 8 ̊20’N Seamount Chain to better understand the melting and transport processes in the southern portion of the 9 ̊-10 ̊N segment of the East Pacific Rise (EPR). The 8 ̊20’N Seamount Chain extends ~160 km west from its initiation, ~15km northwest of the EPR-Siqueiros ridge transform intersection (RTI). To investigate the emplacement of the 8 ̊20’N Seamounts, shipboard EM-122 multibeam, BGM-3 gravity, and towed magnetometer data were collected using the R/V Atlantis in November 2016. Multibeam data show that the seamount chain is characterized by the emplacement of discrete seamounts in the distal portion of the chain, while east of 105 ̊20’ W, the chain is a nearly-continuous volcanic ridge comprised of small cones and coalesced edifices with some evidence for rift zones, craters and calderas on the larger constructs. Isostatic anomalies, calculated along several profiles crossing the main edifices of the seamount chain, indicate that the seamounts formed within 100 km of the EPR ridge axis. Excess crustal thickness variations of 0.5 to 1 km, derived from the Residual Mantle Bouguer Anomaly, suggest an increase in melt flux eastward along the chain. Consistently high emplacement volumes are observed east of -105 ̊20’ W, ~130 km from the ridge axis corresponding with lithosphere younger than 2 Myr. Inverted three-dimensional magnetization data indicate that the seamounts have recorded a series of magnetic reversals along the chain, which correlate to reversals recorded in the surrounding seafloor upon which the seamounts were built. However, reversals along the eastern portion of the chain appear skewed to the west indicating that seamount formation is likely long-lived. The geophysical observations indicate that the overall seamount chain is age progressive, and suggest a coeval volcanism in a region 15-100km from the EPR. The seamounts do not follow absolute plate motions, but are located consistently 15-20 km north of the Siqueiros fracture zone, which further suggests that their formation is linked to the location and tectonic evolution of the Siqueiros-EPR ridge-transform intersection. These findings have implications for the location/origin of the melt region feeding the EPR as well as how melt is transported near a fracture zone. In fact, the seamounts chain does not follow an hotspot reference frame, but instead runs parallel to the fracture zone, at a constant distance. This observation is unusual, compared to the other seamounts in the region. Evidences of plate direction rotation in variation of the main trend of the chain can be observed. They can be attributed to events of plate rotations that characterized the evolution of the Siqueiros Transform Fault as according to Pockanly et al., (1997): the seamount chain may have formed with the first event of plate reorganization from 3.5 Ma, with the inset of the volcanism close to the RTI. We could think about a melt migration model that takes into account the tectonic evolution of the area, pointing out the role of a stress concentration in the vicinity of the RTI as triggering mechanism for the volcanism
Calderas: structure, unrest, magma transfer and eruptions.
No full textCalderas are subcircular depressions resulting from the withdrawal of magma from the chamber to feed an eruption or an intrusion. Calderas are often associated with large and long-lived felsic (high in silica content) magmatic systems, but may also occur in mafic (poor in silica content) systems. Felsic calderas host the largest and most explosive and destructive eruptions, at times erupting >1000 km3 of magma (Druitt and Sparks, 1984; Lipman, 1997; Branney and Acocella, 2015). For these explosive eruptions we lack geophysical and geochemical observations of shallow magma transfer and eruption, so that they remain poorly understood. In contrast, mafic calderas may feed large, long-lived effusive eruptions, which are often observed, and which also have the potential of global impact (e.g., the 1783–85 Laki-Grimsvötn eruption in Iceland; Thordarson and Self, 1993). Beside representing a source of extreme hazard, calderas are also exciting environments where multiple geological and geophysical processes, including storage and transport of magma and hydrothermal fluids, response of rock to pressurization and depressurization, deposition and compaction of various materials, interact on a wide range of temporal and spatial scales.
Over the long-term (hundreds to thousands of years), volcanic activity at calderas reveals unique features. Unlike central volcanoes, where most eruptions occur from a vent or crater on the summit of the edifice, at calderas volcanic activity is often scattered over large areas, with up to tens of monogenic vents found within the caldera, along its rim and on the outer slope of its edifice. Eruptive patterns may also shift over the course of the caldera evolution (e.g., Walker, 1984; Newhall and Dzurisin, 1988; Takada, 1997; Corbi et al., 2015). Such complex distributions of eruptive vents make forecasting the location of any future eruptive vent opening particularly challenging.
Also in the shorter-term (weeks to years) volcanic activity at calderas reveals a distinctive behavior. Calderas are in fact frequently, and for long stretches of time, affected by unrest, i.e., activity deviating from an established baseline of geophysical and geochemical parameters, including shallow seismicity, crustal deformation, degassing. In addition, the pressurization of a hydrothermal system often produces inflation that may mask smaller signals due to shallow magma emplacement, making it hard to recognize whether unrest is magmatic (e.g., Newhall and Dzurisin, 1988). Every caldera experiences at least one episode of unrest every few decades, and some calderas, including Yellowstone (Wyoming, United States), Askja (Iceland) or Aira (Japan) have been restless for a century (Newhall and Dzurisin, 1988; Acocella et al., 2015). Most unrest episodes do not culminate in eruptions, especially at felsic (or silicic) calderas. These felsic calderas are also often associated with resurgence, that is the evident uplift of a portion of their floor over centuries or more (Marsh, 1984; Newhall and Dzurisin, 1988; Acocella et al., 2015; Kennedy et al., 2012; De Silva et al., 2015; Galetto et al., 2017; Acocella, 2019). Due to the apparent lack of recognizable temporal patterns in these frequent states of unrest, that often take place over and again with seemingly erratic temporal evolution, forecasting any impending eruption is particularly difficult. Moreover, it is still unclear how observations from individual unrest episodes should be interpreted in the context of the longer-term, cumulative unrest history, as even a minor perturbation may destabilize a system which may have reached its limit during previous unrest episodes, as observed at Rabaul (Acocella et al., 2015; Kilburn et al., 2017). Unrest leading to eruptions (or eruptive unrest) is usually accompanied by significant seismicity and degassing, lasting only a few months; conversely, unrest not culminating in eruptions (noneruptive unrest) shows minor seismicity and degassing, lasting much longer (Sandri et al., 2017).
Therefore, in addition to challenging our understanding of the formation and dynamics of large and complex magmatic systems, calderas pose significant complications in the temporal and spatial eruptive forecast. Here we contribute to defining these problems and identifying potential solutions by reviewing recent studies on calderas focusing on the processes affecting magma transfer and eruptions, both on the longer- and shorter-term. In particular, we relate the structure of calderas to their state of stress, highlighting how the latter influences shallow magma transport and the location of the eruptive vents. Then we briefly review the unrest processes, to consider the conditions controlling magma eruptibility
Magmatism and tectonics in the Easternmost sector of a transversal fault system in Central Andes: a contribution for Miocene geodynamical evolution of the Andean margin at 24S
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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
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
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