1,721,000 research outputs found
Deep explosive focal depths during maar forming magmatichydrothermal eruption: Baccano Crater, Central Italy
No full textAbstract We describe the eruptive activity of the
Pleistocene composite Baccano maar crater in the
Sabatini Volcanic Complex (Central Italy) combining
stratigraphy, grain size/componentry and rare earth
element and Yttrium (REY) composition of its eruptive
products with the stratigraphy and geothermal data
derived from deep wells drilled on the Baccano structural
high. The main lithological characteristics of the basal
Baccano maar pyroclastic deposit, composed of more
than 60% wt of non-thermometamorphosed lithic clasts
from the sedimentary basement, show that the first
eruption was magmatic-hydrothermal in nature. The
lithology of the sedimentary lithic clasts indicates that
the fragmentation level was at a depth of −1,000 to −1,200 m,
with fragment depth verified by deep well stratigraphy. The
15% wt juvenile non-vesicular glass components suggest that
magma played a minor role in powering the eruption.
Assuming that the high-salinity hot hydrothermal fluids
(365<T<410°C and P∼25 MPa), hosted in the highly
permeable and confined aquifer below the Baccano maar
are representative of those at the time of the eruption, we
propose that hydrofracturing would have triggered the
eruption caused by overpressure at the top of the geothermal
aquifer. REY analysis performed on pyroclastic fragments
and basement rocks suggest that partial dissolution of the
deeper limestones (>−1,400 m) by the aggressive hydrothermal
fluids enriched in acid components (HF, HCl, and
H2SO4) may have contributed to increased CO2 partial
pressure that helped to drive the hydrofracturing. This could
have caused rapid vapour separation and pressure drop,
allowing the almost simultaneous breaking of the aquifer
cover and brecciation of the calcareous units down to −1,000
to −1,200 m depth. The relative abundance of calcareous
lithics in the basal part of the first Baccano eruptive unit,
representing about the upper 200 m of stratigraphy below the
top of the Baccano structural high, reveals the descent of the
piezometric surface during the eruption. Combining deep
well information and maar product stratigraphy, using also
REY data from maar pyroclastic fragments and the basement
rocks we draw an interpretative model for the Baccano maarforming
eruption, concluding that a) magmatic-hydrothermal
eruptions may originate deeper than previously thought,
and b) hydrothermal fluids circulating in limestone
aquifers m
Modes of stepwise eastwardmigration of the northern Tyrrhenian Sea back-arc extension: Evidences from the northern Latium offshore (Italy)
No full textThe structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc basin
has been defined reinterpreting a public data set made up by seismic reflection profiles. A detailed
reconstruction of the extensional front migration trough time across the area has been achieved. Migration
has been defined by identifying the generation of unconformities in the graben-like basins developed in the
area, as due to the activation and deactivation of normal faults. Such phenomena are part of a tectonic
process that also involved blocks rotation, crustal thinning, and stretching. Syn-rift extension affected the
area since the early to middle Miocene (our estimate), principally interesting the north-westernmost sectors.
During late Miocene and throughout the Plio-Quaternary the extensional front moved stepwise toward the
southeastern and eastern sectors. Widespread postrift conditions established over the whole area since the
late Pliocene to early Pleistocene. Since the Quaternary, the locus of active extension further migrated toward
the present onshore area, where a pronounced volcanic phase developed. In this evolutionary framework the
rates of observed migration could be correlated with the acceleration of Calabrian slab rollback since
Pliocene. Furthermore, direct evidences of magmatism were not recognized in the offshore. Although the
observed crustal thinning, the absence of volcanic bodies in the study area could be related to normal faults
which were unable to sufficiently extend the crust, in association with lower crust and mantle processes
unable to produce melts
©2014 American Geophysical Union. All rights reserved. Modes of stepwise eastward migration of the Northern Tyrrhenian Sea back-arc extension: evidences from the Northern Latium offshore (Italy)
No full textThe structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc
basin has been defined reinterpreting a public dataset made up by seismic reflection profiles.
A detailed reconstruction of the extensional front migration trough time across the area has
been achieved.
Migration has been defined by identifying the generation of unconformities in the graben-like
basins developed in the area, as due to the activation and deactivation of normal faults. Such
phenomena are part of a tectonic process that also involved blocks rotation, crustal thinning
and stretching.
Syn-rift extension affected the area since the ?Early-Middle Miocene, principally interesting
the north-westernmost sectors. During late Miocene and throughout the Plio-Quaternary the
extensional front moved stepwise toward the southeastern and eastern sectors. Widespread
post-rift conditions established over the whole area since the late Pliocene-early Pleistocene.
Since the Quaternary the locus of active extension further migrated toward the present
onshore area, where a pronounced volcanic phase developed.
In this evolutionary framework the rates of observed migration could be correlated with the
acceleration of calabrian slab roll-back since Pliocene.
Furthermore direct evidences of magmatism were not recognized in the offshore. Although
the observed crustal thinning, the absence of volcanic bodies in the study area could be
related to normal faults which were unable to sufficiently extend the crust, in association with
lower crust and mantle processes unable to produce melts
The 2012 Ferrara seismic sequence: Regional crustal structure, earthquake sources, and seismic hazard
No full textInadequate seismic design codes can be dangerous, particularly when they underestimate the true hazard. In this study we use data from a sequence of moderate-sized earthquakes in northeast Italy to validate and test a regional wave propagation model which, in turn, is used to under- stand some weaknesses of the current design spectra. Our velocity model, while regionalized and somewhat ad hoc, is consistent with geophysical observations and the local geology. In the 0.02–0.1 Hz band, this model is validated by using it to calculate moment tensor solutions of 20 earth- quakes (5.6 MW 3.2) in the 2012 Ferrara, Italy, seismic sequence. The seismic spectra observed for the relatively small main shock significantly exceeded the design spectra to be used in the area for critical structures. Observations and synthetics reveal that the ground motions are dominated by long-duration surface waves, which, apparently, the design codes do not adequately anticipate. In light of our results, the present seismic hazard assessment in the entire Pianura Padana, including the city of Milan, needs to be re-evaluated. Citation: Malagnini, L., R. B. Herrmann, I. Munafò, M. Buttinelli, M. Anselmi, A. Akinci, and E. Boschi (2012), The 2012 Ferrara seismic sequence: Regional crustal structure, earthquake sources, and seismic hazard, Geophys. Res. Lett., 39, L19302, doi:10.1029/ 2012GL053214.PublishedL193024T. Fisica dei terremoti e scenari cosismiciJCR Journalope
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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