1,721,051 research outputs found
Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy
No full textEmploying 3D finite element method, we develop an algorithm to calculate gravity changes
due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We
consider different source models, such as sphere, spheroid and sill, dilating in elastic media
(homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to
reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera
(Italy), during the 1982-84 unrest episode. The source shape and the characteristics of the
medium have great influence in the calculated gravity changes, leading to very different values
for the source densities. Indeed, the gravity residual strongly depends upon the shape of the
source. Non negligible contributions also come from density and rigidity heterogeneities within
the medium. Furthermore, if the caldera is elasto-plastic, the resulting gravity changes exhibit
a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the
source ranges from ∼ 400 kg/m3 (supercritical water) to ∼ 3300 kg/m3 (higher than trachytic
basalts), with drastically different implications for risk assessment
Analisi tecnico economica dei costi di investimento e di esercizio relativi alle innovazioni delle tecniche di irrigazione
No full textA new interpretation of the 1982-84 unrest at Campi Flegrei Caldera (Italy) by numerical inversion
No full textThe 1982-84 unrest episode at Campi Flegrei was characterized by huge deformation
(about 1.8 m uplift) located inside the caldera and significant gravity variations correlated
with the elevation changes (about -213 μGal/m). Due to the bell shape of the
uplift, the source is usually interpreted to have a fixed spherical shape. In the present
study, we combine simple point source mechanisms (dipoles and double couples) to
represent arbitrary sources such as sphere, ellipsoid or sill. The models are realized
by Finite Element and the medium may be characterized by elastic heterogeneities.
We study the deformation detected by leveling and EDM techniques by coupling the
FE forward models with an inversion procedure. The potential point sources are contained
in a volume of 8×8×8 km3 located beneath Pozzuoli, the site of maximum
displacement. We calculate the displacement field at each data point for each basic
mechanism and we compare the result with the observed value. From the inversion of
geodetic data we retrieve the best-fitting source parameters, without fixing the shape
a priori. The best-fitting source is located beneath Pozzuoli at about 4.8 km b.s.l. and
undergoes to horizontal compression and vertical dilatation
Inversions by 3D finite element solutions: deformation of Mount Etna from 1993 to 1997
No full textInversions of geodetic data are usually performed by using analytical forward models.
Very few analytical solutions exist, and they are characterized by fixed source geometry
(e.g. planar dislocation, sphere, dike) and simplified medium properties (e.g.
homogeneous, flat and elastic halfspace). These assumptions can potentially bias the
estimation of realistic source parameters. We develop a general tool to perform inversions
of geodetic data taking into account lateral variations of mechanical properties
of the medium and effects due to the topographic relief. The forward models are realized
by Finite Element technique. The deformation source is a combination of simple
point source mechanisms, i.e. dipoles and double couples. The FE forward technique
is based on the equivalence, under specific conditions, of the element-source and the
deformation of a 3D ellipsoid dilating under a constant pressure. This procedure is
applied to study the inflation process on Mount Etna from 1993 to 1997, as evidenced
by data recorded by GPS stations, EDM measurements and analysis of InSAR images.
We build a matrix of displacement solutions at data points for each potential elementsource.
We consider forward models characterized by heterogeneous medium and topographic
free surface. A direct search is performed in the parameters space using the
neighbourhood algorithm followed by an appraisal of the sampled solutions. From the
inversions we retrieve a source located below the NW sector of Etna, at 6-7 km b.s.l.
Our results suggest that while the effect of topography can be negligible, elastic heterogeneities
in the medium can significantly alter the position of the inferred source.
Furthermore, since the data show a significant signal in the SE sector due to flank
instability, we also include in our study some simple sliding mechanisms
Geometrical and physical properties of the 1982-84 deformation source at Campi Flegrei - Italy
No full textDeformation of the ground surface in volcanic areas is generally recognized as a reliable indicator of unrest, possibly
resulting from the intrusion of fresh magma within the shallow rock layers. The intrusion process is usually
represented by a deformation source such as an ellipsoidal pressurized cavity, embedded within a homogeneous and
elastic half-space. Similar source models allow inferring the depth, the location and the (incremental) volume of the
intrusion, which are very important parameters for volcanic risk implications. However, assuming a homogeneous
and elastic rheology and, assigning a priori the shape and the mechanism of the source (within a very restricted
“library” of available solutions) may bias considerably the inference of source parameters. In complete generality,
any point source deformation, including overpressure sources, may be described in terms of a suitable moment
tensor, while the assumption of an overpressure source strongly restricts the variety of allowable moment tensors.
In particular, by assuming a pressurized cavity, we rule out the possibility that either shear failure may precede
magma emplacement (seismically induced intrusion) or may accompany it (mixed tensile and shear mode fracture).
Another possibility is that a pre-existent weakness plane may be chosen by the ascending magma (fracture
toughness heterogeneity). We perform joint inversion of levelling and EDM data (part of latter are unpublished),
collected during the 1982-84 unrest at Campi Flegrei caldera: a 43% misfit reduction is obtained for a general
moment source if the elastic heterogeneities computed from seismic tomography are accouted for. The inferred
source is at 5.2 km depth but cannot be interpreted as a simple pressurized cavity. Moreover, if mass conservation
is accounted for, magma emplaced within a shallow source must come from a (generally deeper) reservoir, which
is usually assumed to be deep enough to be simply neglected. At Campi Flegrei, seismic tomography indicates
that the “deep” magma source is rather shallow (at 7-8 km depth), so that its presence should be included in any
thorough attempt to source modeling. Taking into account a deflating source at 7.5 km depth (represented either as
a horizontal sill or as an isotropic cavity) and an inflating moment source, the fit of both levelling and EDM data
improves further (misfit reduction 80%), but still the best fitting moment source (at 5.5 km depth) falls outside the
range of pressurized ellipsoidal cavities. The shallow moment source may be decomposed in a tensile and a shear
dislocation. No clue is obtained that the shear and the tensile mechanisms should be located in different positions.
Our favourite interpretation is in terms of a crack opening in mixed tensile and shear mode, as would be provided
by fluid magma unwelding pre-stressed solid rock. Although this decomposition of the source is not unique, the
proposed solution is physically motivated by the minimum overpressure requirement. An important implication of
this new interpretation is that the magma emplaced in the shallow moment source during the 1982-84 unrest was
not added to already resident magma at the same position
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
Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy
No full textEmploying a 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized
sources of any shape in elastic and inelastic heterogeneous media. We consider different source models, such as
sphere, spheroid and sill, dilating in elastic media (homogeneous and heterogeneous) and in elasto-plastic media.
The models are oriented to reproduce the gravity changes and the surface deformation observed at Campi
Flegrei caldera (Italy), during the 1982-1984 unrest episode. The source shape and the characteristics of the
medium have great influence on the calculated gravity changes, leading to very different values for the source
densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions
also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto-
plastic, the resulting gravity changes exhibit a pattern similar to that provided by a low effective rigidity. Even
if the variation of the source volumes is quite similar for most of the models considered, the density inferred for
the source ranges from ∼400 kg/m3 (super critical water) to ∼3300 kg/m3 (higher than trachytic basalts), with
drastically different implications for risk assessment.Published119-1333.6. Fisica del vulcanismoJCR Journalope
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
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