Common geophysical characteristics of Campi Flegrei, Rabaul and Usu: Three volcanic events

Volcanogenic deformations during periods of unrest are related to volcanic seismicity in various ways. Magmas or geothermal fluids intrude beneath volcanoes and cause deformations at the surface gradually or rapidly. Mechanical energies of the intrusions are converted to deformation energy, earthquakes, and also explosions under certain circumstances. Partition among the three kinds of energies provides information of the internal processes and yields a clue to their origin. From the above standpoint, deformations accompanying seismicity at Campi Flegrei, Rabaul and Usu are discussed with the aid of published data. To quantitatively correlate the deformations and the seismicity, we discuss the time-derivatives of uplift and release of seismic energy, which are energetically interrelated. The correlation between them is moderate at Campi Flegrei, somewhat higher at Rabaul and high at Usu, but the data sets are not always equal in quality. The deformation volumes are also different among the three volcanoes. In order to standardize the volumes, seismic energies released by unit volume of each deformation are compared. The specific seismic energy is found to increase from Campi Flegrei through Rabaul to Usu. Such different behavior in seismodeformations among the three volcanoes is interpreted as differences in the mechanism of volcanic activity, and in physical properties of the mediums involved

Duality Symmetry and Plane Waves in Non-Commutative Electrodynamics

We generalise the electric-magnetic duality in standard Maxwell theory to its non-commutative version. Both space-space and space-time non-commutativity are necessary. The duality symmetry is then extended to a general class of non-commutative gauge theories that goes beyond non-commutative electrodynamics. As an application of this symmetry, plane wave solutions are analysed. Dispersion relations following from these solutions show that general non-commutative gauge theories other than electrodynamics admits two waves with distinct polarisations propagating at different velocities in the same direction.Comment: 13 pages, PlainTeX. A reference and an equation (Ref.[11] and eq.(4.16)) are added, the text is amended, and some contents are deleted. Errors in some equations ((4.13), (4.14), (4.15) and (4.19)) are correcte

MISURE GRAVIMETRICHE ALL’ISOLA DI PANTELLERIA

Nel mese di giugno 2009 è stata condotta una campagna gravimetrica di precisione all’isola di Pantelleria, dove le misure vengono effettuate con una periodicità biennale data la debole attività dell’isola. Le misure sono state rilevate sull’intera rete che è costituita da 24 stazioni (figura 1), molte delle quali ubicate su vertici della locale linea di livellazione e tutte collegate a due stazioni assolute istituite nel 1993 rispettivamente a Pantelleria e a Khamm

Thirty years of precise gravity measurements at Mt. Vesuvius: an approach to detect underground mass movements

Since 1982, high precision gravity measurements have been routinely carried out on Mt. Vesuvius. The gravity network consists of selected sites most of them coinciding with, or very close to, leveling benchmarks to remove the effect of the elevation changes from gravity variations. The reference station is located in Napoli, outside the volcanic area. Since 1986, absolute gravity measurements have been periodically made on a station on Mt. Vesuvius, close to a permanent gravity station established in 1987, and at the reference in Napoli. The results of the gravity measurements since 1982 are presented and discussed. Moderate gravity changes on short-time were generally observed. On long-term significant gravity changes occurred and the overall fields displayed well defined patterns. Several periods of evolution may be recognized. Gravity changes revealed by the relative surveys have been confirmed by repeated absolute measurements, which also confirmed the long-term stability of the reference site. The gravity changes over the recognized periods appear correlated with the seismic crises and with changes of the tidal parameters obtained by continuous measurements. The absence of significant ground deformation implies masses redistribution, essentially density changes without significant volume changes, such as fluids migration at the depth of the seismic foci, i.e. at a few kilometers. The fluid migration may occur through pre-existing geological structures, as also suggested by hydrological studies, and/or through new fractures generated by seismic activity. This interpretation is supported by the analyses of the spatial gravity changes overlapping the most significant and recent seismic crises

MODELING OF GAS COMPOSITION AND GRAVITY SIGNALS AT THE PHLEGREAN FIELDS CALDERA

Hydrothermal systems are known to play an important role in the evolution of active calderas: these volcanic systems periodically undergo dramatic unrest crises, commonly involving ground deformation, seismic activity and important changes in several geophysical and geochemical parameters monitored at the surface. These unrest crises may, or may not, culminate with a renewal of the eruptive activity, but in any case they bear important consequences in densely populated regions. Early warning and a prompt evaluation of the state of evolution of the volcanic system are therefore essential to ensure proper mitigation measures. A proper interpretation of monitoring data, however, is only achieved within the framework of a robust conceptual model of the system. Recent research work carried out at the Phlegrean Fields shows that the recent evolution of the caldera is consistent with the presence of a pulsating magmatic source, periodically discharging CO2-enriched fluids into a shallow hydrothermal system. Such pulsating degassing affects the amount of heat and fluids entering the hydrothermal system, the distribution of fluid phases throughout the system, and their composition. As a consequence, degassing controls not only the composition of fluids discharged at the surface, but also ground displacement and gravity residuals. In this work, the TOUGH2 code has been applied to study how different degassing scenarios could affect the composition of discharged fluids and the gravity signals recorded at the surface

Toward Absolute Gravity Networks to Monitor the Neapolitan Volcanoes

As well known, measurements of the time-space changes of the gravity field are a powerful approach to detect the masses change/redistribution in the underground, such as those at volcanoes. The most common approach to detect gravity precursory signals is the use of repeated relative measurements at benchmarks on networks. This is very good, but has some and significant limits: 1) the networks must be linked to a reference station stable over long time and if possible external to the active area. This is quite simply for land volcanoes, but is generally difficult for volcanoes on islands, particularly when far from the terra firma; 2) to reach high precision, measurements require special operative procedure implying long time surveys; 3) relative gravity changes can be affected over the long-time by changes of instrumental sensitivity and loss of vacuum in the air-tight sealing system, therefore the instruments must be subject to continuous check. Measurements on network have the advantage to permit to define the position and the geometry of the masses change/redistribution, even if they suffer from the lack of information about the rate and/or quick changes, since variations are assumed linearly changing over the time between two consecutive surveys, usually spaced out some months or years. This is a fundamental information in the prediction of the volcanic activity changes and/or of volcanic eruptions and leads to conclude that measurements on networks cannot be excluded from a monitoring program, but moving toward absolute methodologies is advisable. Nowadays, and since some years, this is possible due to the commercially availability of a portable field absolute gravimeter (Micro-g_LaCoste A10), which we acquired at the end of 2014. The main advantages of the absolute measurements on networks are: i) they are independent from any reference and the field operation are faster and easier, permitting much frequent measurements and reducing the lack of information between two consecutive surveys; ii) they are directly linked to standards of time and length therefore fairly independent from instrumental references and drift, avoiding loss of long-term information; iii) the measured value can be used without loop reductions, post processing and benchmark links. This can be translated into large advantages, such as saving of human resources, survey’s time and costs. Before to start field surveys, we carried out several measurements to test the performances of the instrument and mainly to verify the repeatability of the measured value. The test was performed at the Old Building of the Osservatorio Vesuviano, on Mount Vesuvio, that is a very low noised and good logistic site; it is one of the absolute stations installed in 80’s in the Neapolitan area which value has been measured several time till 2010. In June 2015, starting from Campi Flegrei, we set the first absolute gravity networks on the Neapolitan volcanoes, formed by stations coinciding or close to the benchmarks of the already existing relative networks. Here we present and discuss the data collected during the test and the field surveys; we also will describe the new absolute networks

Misure gravimetriche a L’Aquila. Confronto con i valori rilevati nel 1995

Nel febbraio 2010 si è dato inizio alla realizzazione di una rete gravimetrica a L’Aquila con l’istituzione di una stazione assoluta. La stazione è stata realizzata nel Palazzo Comunale della città di L’Aquila (Palazzo Margherita – foto a), nel centro della città, in un locale al piano terra (foto b). Sono state effettuata anche misure gravimetriche relative al fine di misurare il locale gradiente verticale della gravità (foto c) e riportare il valore assoluto ad una stazione satellite esterna all’edificio (foto d). Nel corso della campagna è stato anche effettuato il collegamento gravimetrico tra la nuova stazione e quella istituita nel 1995 nei laboratori sotterranei dei Laboratori Nazionali del Gran Sasso (LNGS) (foto e) dove è stato anche misurato il gradiente verticale. Tale punto fu allora istituito quale nodo fondamentale della costituenda “Rete Gravimetrica Nazionale di Ordine Zero”