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Prattes et al. (2011) report ULF magnetic anomalous signals claiming them to be possibly precursor of the 6 April 2009 M W = 6.3 L'Aquila earthquake. This comment casts doubts on the possibility that the observed magnetic signatures could have a seismogenic origin by showing that these pre-earthquake signals are actually part of normal global geomagnetic activity. © 2012 Author(s). CC Attribution 3.0 License.

Scotto C.,Istituto Nazionale di Geofisica
Advances in Space Research | Year: 2011

An algorithm is proposed for evaluation of the probability of occurrence of an F1 layer or L condition, based on tables. Observations independent of the tables database are used for comparison between the estimated probability of occurrence, the formulation used at present in IRI, and the occurrence actually observed. The importance of the inclusion of L condition in the electron density profile model is shown. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

Berrino G.,Istituto Nazionale di Geofisica | Yokoyama I.,Hokkaido University
Geofisica Internacional | Year: 2011

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.

Kahl M.,University of Leeds | Kahl M.,Ruhr University Bochum | Chakraborty S.,Ruhr University Bochum | Pompilio M.,Istituto Nazionale di Geofisica | Costa F.,Nanyang Technological University
Journal of Petrology | Year: 2014

Deciphering the evolution of the internal dynamics of magmatic plumbing systems and identifying the key parameters that drive such dynamics are major goals of modern volcanology. Here we present a novel petrological approach that combines kinetic modelling of the diffusive relaxation of chemical zoning patterns in olivine crystals with thermodynamic modelling (MELTS) to constrain the nature and evolution of the plumbing system of Mt. Etna and the processes governing its internal dynamics. We investigated the compositional and temporal record preserved in 180 olivine crystals that were erupted between 1991 and 2008. Detailed systemization of the information stored in the sequential zoning record of the olivines reveals the existence of at least five compositionally different magmatic environments (MEs), characterized by different olivine compositions: M0 (Fo79-83), M1 (Fo75-78), M2 (Fo70-72), M3 (Fo65-69) and mm1 (Fo73-75). Several routes of magma transfer connect these environments. We identified three prominent magma passageways between the environments M0:M1, M2:mm1 and M1:M2 that were active during the entire period of observation between 1991 and 2008. Modelling the diffusive relaxation of the olivine zoning patterns reveals that the transfer of magma along such routes can occur over fairly heterogeneous timescales ranging from days to 2 years. Although some of the passageways have been sporadically active in the months and sometimes years before an eruption, the magma migration activity increases clearly in the weeks and days prior to an eruptive event. In this context, major transfer routes such as M2:mm1 might represent temporary passageways that are activated only shortly before eruptive events. A forward modelling approach was developed using thermodynamic calculations with the MELTS software to identify the key intensive variables associated with the different magmatic environments. In this approach the observed populations of mineral compositions (e.g. Fo79-83), rather than single compositions, are associated with thermodynamic parameters [pressure, temperature, water content, oxygen fugacity (fO2) and bulk composition of the melt] to identify the most plausible set corresponding to each ME. We found that temperature, water content and possibly oxidation state are the main distinguishing features of the different magmatic environments. The most primitive olivine population M0 (Fo79-83) and some of its associated clinopyroxenes formed at high melt water contents (3·5-5·2 wt %), at fO2 conditions buffered at quartz-fayalite-magnetite (QFM) or Ni-NiO (NNO), at temperatures ≥ 1110°C and at pressures ranging between 1·5 and 3·0 kbar (or higher). The intermediate population M1 (Fo75-78) can be produced over a broad spectrum of conditions, but all require similar temperatures and lower water contents (0·1-1·4 wt %). The most evolved, more Fe-rich olivines of M2 and M3 are products of melts with much lower water contants (0·2-1·1 wt % H2O for M2, <0·5 wt % H2O for M3), and at probably somewhat more reducing (QFM) conditions at somewhat lower temperatures (~1080°C). The M3 environment characterized by very low water contents and reducing conditions could be related to an enhanced flux of CO2. Combination of the characteristics of the various magmatic environments with temporal information (residence time in different environments and timing of magma transfer between these environments) allows a dynamic model of the plumbing system beneath Mt. Etna to be constructed. © The Author 2015.

Godano C.,The Second University of Naples | Tramelli A.,Istituto Nazionale di Geofisica
Pure and Applied Geophysics | Year: 2016

The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue. © 2016, Springer International Publishing.

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