1,721,058 research outputs found
Numerical evidences enabling to reconcile gravity and height changes in volcanic areas
No full textGravity and height changes, reflecting magma accumulation in subsurface chambers, are evaluated using Finite Element models in order to resolve controversial relationships observed in some volcanic areas. When significant gravity changes occur without any significant deformation, or vice versa, it is often difficult, if not impossible, to jointly explain the observations using the popular Mogi model. Here we explore whether these discrepancies can be explained by magma compressibility and source geometry effects. Compression of resident magma and expansion of the chamber wall act concurrently to accommodate newly added magma. Gravity-height ratios are found to mainly depend on: (i) geometry of the sources, which control the volume expansion of the chamber, (ii) magma compressibility, which affects the contraction of the magma resident in the chamber, and (iii) depth of the sources. Our numerical results show that, when magma compressibility and non-spherical sources are taken into account, significant gravity variations can, indeed, be successfully reconciled with negligible height changes. This may be the case at Etna volcano, where gravity changes (about 40 miuGal) without any significant deformation (below 5 cm) were observed during the 1994-1995 inflation period. The numerical results point to the accumulation of a 1.4x10^10 kg mass into an elongated source simulating a shallow storage region supplying the summit craters.Published164-1734V. Vulcani e ambienteJCR Journalrestricte
The Dewatering of the Fucino Lake Did Not Promote the M7.1 1915 Fucino Earthquake: Insights From Numerical Simulations
Full text linkThe powerful M7.1 earthquake that devastated the Fucino Basin (Central Italy) in 1915 results to be the only (except for a M5.7 event in 1904) remarkable event to have occurred in that area, according to the 900-year-long record of the Italian Seismic Catalogue. Curiously, the 1915 event occurred only 38years after the complete man-induced dewatering of the largest lake of peninsular Italy, which formerly occupied the basin. Hence, we investigate on a possible relationship between the dewatering of the lake and the occurrence of the 1915 earthquake. We perform some numerical simulations in order to estimate the stress changes induced by the dewatering of the Fucino Lake and by the 1904 earthquake. We compute the stress changes on two different seismogenic sources selected among the ones proposed in the literature. Our main results support that (1) the dewatering process has reduced effects of the state of stress in the area before the 1915 earthquake, (2) the primary effect of the dewatering on both sources is a decrease of stresses that hampers the slip on the fault planes, and (3) the positive stress changes associated to the 1904 event would be too weak to influence the occurrence of the 1915 earthquake. We also suggest that the dewatering may have delayed by 1.7years the 1915 earthquake occurrence. Plain Language Summary The powerful M7.1 earthquake that devastated the Fucino Basin (Central Italy) in 1915 occurred only 38years after the complete man-induced dewatering of the largest lake of peninsular Italy, which formerly occupied the basin. Hence, we investigate on a possible relationship between the dewatering of the lake and the occurrence of the 1915 earthquake. We find that the stress changes originated by the Fucino Lake dewatering represent the main factor of perturbation in the area prior to 1915; however, such a dewatering process may have only slightly (a couple of years) delayed the occurrence of the strong rupture of the 1915 earthquake. Our work confirms the possibility that human activities can induce a temporal delay in the occurrence of future earthquakes. Key Point
Evidence of a shallow persistent magmatic reservoir from joint inversion of gravity and ground deformation data: The 25-26 October 2013 Etna lava fountaining event
Full text linkTo evaluate the volcanic processes leading to the 25-26 October 2013 lava fountain at Mount Etna, we jointly investigated gravity, GPS, and DInSAR measurements covering the late-June to early-November time interval. We used finite element modeling to infer a shallow magmatic reservoir which (i) inflated since July 2013, (ii) fed the volcanic activity at the summit craters during 25-26 October, and (iii) deflated due to magma drainage related to this volcanic activity. We suggested that this reservoir belongs to a shallow volume, which is located beneath the summit area and is replenished by magma rising from deep reservoirs and fed the short-term volcanic activity, representing a persistent shallow magmatic plumbing system of Etna. In addition, the model results show that there is a large discrepancy between the erupted and shallow reservoir deflation volumes, which could be reasonably attributable to a highly compressible volatile-rich magma
Time dependent piezomagnetic fields in viscoelastic medium
No full textWe investigated time dependent piezomagnetic fields due to volcanic sources embedded in a
viscoelastic, homogeneous half-space. Especially in volcanic areas, the presence of inhomogeneous
materials and high temperatures produce a lower effective viscosity of the Earth’s
crust that calls for considering anelastic properties of the medium. Piezomagnetic properties
are carried by grains of titano-magnetite, which occupy only a small fraction of ordinary rock
volume and are supposed to be elastic, while the non-magnetic surrounding matrix is assumed
to be viscoelastic. From all the possible rheological models, we investigated two cases in which
the bulk modulus is purely elastic and the shear modulus relaxes as: (i) a Maxwell solid and
(ii) a standard linear solid (SLS). We applied the Correspondence Principle to the analytical
elastic solutions for pressurized spherical sources and dislocation sources in order to determine
the time dependent piezomagnetic fields in a viscoelastic medium. The piezomagnetic field
completely vanishes after the relaxation process for a Maxwell rheology, whereas it is found
to decrease over time and reach some finite offset value for a SLS rheology. These different
behaviours provide helpful hints in understanding the temporal evolution of piezomagnetic
anomalies in volcanic regions.Published536-5483.6. Fisica del vulcanismoJCR Journalreserve
Numerical modeling of deformation and stress fields around a magma chamber: constraints on failure conditions and rheology
No full textWe present a stress-strain analysis using the Finite Element Method to investigate failure conditions of pressured magma chambers embedded in an inelastic domain. The pressure build-up induces variations in the stress field until failure conditions are reached. Therefore, the definition of the failure conditions could have a significant impact on the volcano hazard assessment. Using a numerical approach, we analyze the stresses in a gravitationally loaded model assuming a brittle failure criterion, to determine the favorable conditions for magma chamber failure in different source geometries, reference stress states, pore fluid pressures, rock rheologies and topographic profiles. The numerical results allow us to pinpoint the conditions promoting seismicity near the magma chamber. The methodology places a limit on the pressure that a magma chamber can sustain before failing and provides a quantitative estimate of the uplift expected at the ground surface. Thermally-activated ductile regimes, which may develop in the region surrounding a heated magma chamber, are also investigated. The stress relaxation in a ductile shell may prevent the wall rupture, favoring the growth of large overpressured chambers, which could lead to considerable deformation at the ground surface without significant seismicity. The numerical results suggest that a spherical source, compressive regime, gentle edifice topography, and growth of a ductile shell are important factors for the initial formation and the mechanical stability of magma storage systems. On the other hand, an elongated ellipsoidal source, extensional regime, steep volcano topography and high pore fluid pressure lower the overpressure necessary for inducing failure. These findings could help in gaining insights on the internal state of the volcano and, hence, in advancing the assessment of the likelihood of volcano unrest.Published14-274V. Vulcani e ambienteJCR Journalrestricte
Reconstructing the Vulcano Island evolution from 3D modeling of magnetic signatures
No full textHigh-resolution ground and marine magnetic data are exploited for a detailed definition of a 3D model of the
Vulcano Island volcanic complex. The resulting 3D magnetic imaging, obtained by 3-D inverse modeling
technique, has delivered useful constraints both to reconstruct the Vulcano Island evolution and to be used as
input data for volcanic hazard assessment models. Our results constrained the depth and geometry of
the main geo-structural features revealing more subsurface volcanic structures than exposed ones and allowing
to elucidate the relationships between them. The recognition of two different magnetization sectors,
approximatively coincident with the structural depressions of Piano caldera, in the southern half of the island,
and La Fossa caldera at the north, suggests a complex structural and volcanic evolution.Magnetic highs identified
across the southern half of the island reflect the main crystallized feeding systems, intrusions and buried vents,
whose NNW–SSE preferential alignment highlights the role of the NNW–SSE Tindari–Letojanni regional system
from the initial activity of the submarine edifice, to the more recent activity of the Vulcano complex. The low
magnetization area, in the middle part of the islandmay result fromhydrothermally altered rocks. Their presence
not only in the central part of the volcano edifice but also in other peripheral areas, is a sign of a more diffuse
historical hydrothermal activity than in present days. Moreover, the high magnetization heterogeneity within
the upper flanks of La Fossa cone edifice is an imprint of a composite distribution of unaltered and altered
rocks with different mechanical properties, which poses in this area a high risk level for failure processes
especially during volcanic or hydrothermal crisis.Published40-491V. Storia e struttura dei sistemi vulcaniciJCR Journalrestricte
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
The borehole dilatometers network of Etna.
No full textDopo una lunga fase preparatoria sull’Etna è stata installata una rete composta da 4 dilatometri installati in pozzi profondi. Questa attività è avvenuta in due fasi successive (2010-2011 e 2013) supportate da altrettanti progetti di ricerca. I dilatometri da pozzo sono installati in fori trivellati a profondità solitamente maggiori di 100 m, e misurano lo strain volumetrico a cui è sottoposta la roccia circostante potenzialmente con precisioni nominali fino a 10-12 in un ampio intervallo di frequenze (10-7 – 102 Hz). In questo lavoro sono illustrate le caratteristiche degli apparati utilizzati, le metodologie di installazione in pozzo, e le problematiche della gestione strumentale. Vengono poi descritti i risultati delle calibrazioni strumentali ottenute dopo l’installazione tramite le differenti metodologie. Sono inoltre illustrati i risultati ottenuti dalle variazioni di strain registrate nel breve termine durante le numerose fontane di lava emesse dall’Etna nel periodo2011-2013, e sono anche presentate le variazioni di segnale registrare a tutte le stazioni durante l’ultima fontana di lava del 28 Dicembre 2014. Infine sono anche mostrate le potenzialità del segnale a rilevare nel medio-lungo termine variazioni significative connesse a differenti fasi dell’attività vulcanica.
After a long preparatory phase on Etna a network of 4 borehole dilatometers has been installed. This activity took place in two successive phases (2010-2011 and 2013) supported by two research projects. The borehole dilatometers are installed in holes drilled at depths usually greater than 100 m, and they measure the volumetric strain of the surrounding rock potentially with nominal precision up to 10-12 in a wide frequency range (10-7 – 102 Hz). In this paper we describe the characteristics of the equipment used, the methods for the borehole installations, and the problematic related to the instrumental working. We describe the results of the instrumental calibrations obtained by different methods after the installations. We illustrate the results obtained by the changes of strain recorded in the short-term during the several lava fountains emitted from Etna during 2011-2013, and we also show signal changes recorded at all four stations during the last lava fountain of 28 December 2014. Finally, we show the potential of the signal in the medium-term to detected significant changes related to different stages of volcanic activity.Published1-322V. Dinamiche di unrest e scenari pre-eruttiviN/A or not JCRope
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
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