DSpace Collection:

High precision locations of long-period events at La Fossa Crater (Vulcano Island, Italy)

Tue, 31 Mar 2009 22:00:00 GMT

Title: High precision locations of long-period events at La Fossa Crater (Vulcano Island, Italy) Authors: Gambino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Cammarata, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Rapisarda, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia Abstract: Since the last eruption in 1888-90, the volcanic activity on Vulcano Island (Aeolian Archipelago, Italy) has been limited to fumarolic degassing. Fumaroles are mainly concentred at the active cone of La Fossa in the northern sector of the island and are periodically characterized by increases in the temperature as well as in the amount of both CO2 and He .Seismic background activity at Vulcano is dominated by micro-seismicity originating at shallow depth (<1-1.5 km) under La Fossa cone. This seismicity is related to geothermal system processes and comprises long period (LP) events. LPs are generally considered as the resonance of a fluid-filled volume in response to a trigger. We analyzed LP events recorded during an anomalous degassing period (August-October 2006) applying a high precision technique to define the shape of the trigger source. Absolute and high precision locations suggest that LP events recorded at Vulcano, during 2006, were produced by a shallow focal zone ca. 200 m long, 40 m wide and N30-40E oriented. Their occurrence is linked to magmatic fluid inputs that by modifying the hydrothermal system cause excitation of a fluid-filled cavity.

Geomagnetism and Aeronomy activities in Italy during IGY, 1957/58

Tue, 31 Mar 2009 22:00:00 GMT

Title: Geomagnetism and Aeronomy activities in Italy during IGY, 1957/58 Authors: Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: In 2007 several events were organized to celebrate the fiftieth anniversary of the International Geophysical Year (IGY, 1957-1958). The celebrations will last until 2009 and are taking place within different contexts: the International Polar Year (IPY), the International Heliophysical Year (IHY), the electronic Geophysical Year (eGY) and the International Year of Planet Earth (IYPE). IGY offered a very appropriate and timely occasion to undertake a series of coordinated observations of various geophysical phenomena all over the globe. Italy took part in the broad international effort stimulated by IGY. In fact, Italy participated in observations and studies in many of the proposed scientific areas, in particular Geomagnetism and Aeronomy. The Istituto Nazionale di Geofisica (ING) started the installation of observatories, and updated and ensured continuous recording of geophysical observations. Geomagnetism, ionospheric physics, seismology, and other geophysical disciplines, were advanced. Although much of the work was undertaken in Italy, some attention was also devoted to other areas of the world, in particular Antarctica, where Italy participated in seismological observations. This paper gives a summary of the Geomagnetism and Ionospheric Physics activities within IGY. Furthermore, we highlight the importance of this historical event and its outcomes for the improvement of geophysical observations and the post-IGY growth of scientific investigations in Italy.

Modal decomposition of magnetic maps: the case of Cape Roberts aeromagnetic survey, Antarctica

Wed, 31 Dec 2008 23:00:00 GMT

Title: Modal decomposition of magnetic maps: the case of Cape Roberts aeromagnetic survey, Antarctica Authors: Gambetta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This paper proposes a digital enhancement tool for magnetic anomaly maps. The magnetic anomaly map is decomposed by means of Eigenvalue Decomposition into a number of orthogonal bases. The dataset is then filtered accordingly to a specific variance pattern. The dataset is decomposed and the eigenvalues population is inspected so that the variance is evaluated yielding the definition of two thresholds. Subsequently, the dataset is reconstructed into three subsets which hold different features respectively. The proposed filtering procedure is first tested with a synthetic signal and then applied to the data of Cape Roberts (Antarctica) aeromagnetic survey, flown over an off-shore rift basin. The proposed method appears to be efficient in noise removal and acts as a digital enhancement tool which provides TMI anomaly maps revealing hidden lineaments, otherwise not visible. The methodology effectiveness as a hidden lineaments detection tool has been checked against independent data.

Microgravity vertical gradient measurement in the site of VIRGO interferometric antenna (Pisa plain, Italy)

Tue, 30 Sep 2008 22:00:00 GMT

Title: Microgravity vertical gradient measurement in the site of VIRGO interferometric antenna (Pisa plain, Italy) Authors: Stefanelli, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Carmisciano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Beverini, N.; Dipartimento di Fisica, Università degli Studi di Pisa, Italy; Fidecaro, F.; Dipartimento di Fisica, Università degli Studi di Pisa, Italy; Embriaco, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The site of the European Gravitational Observatory (EGO) located in the countryside near Pisa (Tuscany, Italy) was investigated by a microgravity vertical gradient (MVG) survey. The EGO site houses the VIRGO interferometric antenna for gravitational waves detection. The microgravity survey aims to highlight the gravity anomalies of high-frequency related to more superficial geological sources in order to obtain a detailed model of the lithologic setting of the VIRGO site, that will allow an estimate of the noise induced by seismic waves and by Newtonian interference. This paper presents the results of the gradiometric survey of 2006 in the area of the interferometric antenna. MVG measurements allow us to enhance the high frequency signal strongly associated with the shallow structures. The gradient gravity map shows a main negative pattern that seems related to the trending of the high density layer of gravel that was evidenced in geotechnical drillings executed along the orthogonal arms during the construction of the VIRGO complex. Calibrating the relationship between the vertical gradient and the depth of the gravel interface we have computed a model of gravity gradient for the whole VIRGO site, defining the 3D distribution of the top surface of this layer. This latter shows a NE-SW negative pattern that may represent a palaeo-bed alluvial of the Serchio from the Bientina River system.

Seismological investigations in the Gioia Tauro Basin (southern Calabria, Italy)

Tue, 30 Sep 2008 22:00:00 GMT

Title: Seismological investigations in the Gioia Tauro Basin (southern Calabria, Italy) Authors: Giampiccolo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Musumeci, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Falà, F.; Dipartimento di Scienze Geologiche, Università degli Studi di Catania, Italy; Gresta, S.; Dipartimento di Scienze Geologiche, Università degli Studi di Catania, Italy Abstract: This study provides new seismological information to characterize the seismically active area of the Gioia Tauro basin (southern Calabria, Italy). Seismic activity recorded by a temporary network from 1985 to 1994 was analyzed for focal mechanisms, stress tensor inversion, P-wave seismic attenuation and earthquake source parameters estimation. Fault plane solutions of selected events showed a variety of different mechanisms, even if a prevalence of normal dip-slip solutions with prevalent rupture orientations occurring along ca. NE-SW directions was observed. Stress tensor inversion analysis disclosed a region governed mainly by a NW-SE extensional stress regime with a nearly vertical σ1. These results are consistent with the structure movements affecting the studied area and with geodetic data. Furthermore, evaluation of P-waves seismic attenuation and earthquake source parameters of a subset of events highlighted a strong heterogeneity of the crust and the presence of fault segments and/or weakened zones where great stress accumulation or long-rupture propagation are hindered.

Integrated geophysical survey to recognize ancient Picentia’s buried walls, in the Archaeological Park of Pontecagnano – Faiano (Southern Italy)

Tue, 30 Sep 2008 22:00:00 GMT

Title: Integrated geophysical survey to recognize ancient Picentia’s buried walls, in the Archaeological Park of Pontecagnano – Faiano (Southern Italy) Authors: Fedi, M.; Dipartimento di Scienze della Terra, Università degli studi di Napoli «Federico II», Napoli, Italy; Florio, G.; Dipartimento di Scienze della Terra, Università degli studi di Napoli «Federico II», Napoli, Italy; Garofalo, B.; Centro Regionale di Competenza per lo Sviluppo ed il Trasferimento dell'Innovazione Applicata ai Beni Culturali e Ambientali INNOVA, Pozzuoli (NA), Italy; La Manna, M.; Centro Regionale di Competenza per lo Sviluppo ed il Trasferimento dell'Innovazione Applicata ai Beni Culturali e Ambientali INNOVA, Pozzuoli (NA), Italy; Pellegrino, C.; Dipartimento di Beni Culturali, Laboratorio di Archeologia «M. Napoli», Università di Salerno, Fisciano (SA), Italy; Rossi, A.; Dipartimento di Beni Culturali, Laboratorio di Archeologia «M. Napoli», Università di Salerno, Fisciano (SA), Italy; Soldovieri, M. G.; Dipartimento di Scienze della Terra, Università degli studi di Napoli «Federico II», Napoli, Italy Abstract: There is no information on previous geophysical prospections carried out in the Archaeological Park of Pontecagnano- Faiano, in order to reconstruct the ancient settlement of Picentia, an Etrusco-Campanian and Roman settlement near Salerno (Southern Italy). Therefore, an integrated geophysical survey based on magnetic, geoelectric and ground-penetrating radar (GPR) prospections was executed in the Park. The methods provided a basic map of buried ancient structures at depth from 0.1-0.2 to about 1.5 meters. Magnetic data were processed analyzing the analytical signal of the vertical derivative of the measured gradient and this substantially reduced a strong fence effect. The results of the geophysical prospections showed archaeological structures located close to those discovered in the excavated areas. The shape of the anomalies are usually elongated with well-defined geometrical characteristics. Many anomalies are arranged along orthogonal directions and they are very coherent with the excavated structures, namely the quarters structures of the ancient Picentia.

The 2006 Kythira (Greece), Mw6.7 slab-pull event: tectonic implications and the geometry of the hellenic wadati-benioff zone

Tue, 30 Sep 2008 22:00:00 GMT

Title: The 2006 Kythira (Greece), Mw6.7 slab-pull event: tectonic implications and the geometry of the hellenic wadati-benioff zone Authors: Nikolintaga, I.; Geophysics Department, School of Geology, Aristotle University of Thessaloniki, Greece; Karakostas, V.; Geophysics Department, School of Geology, Aristotle University of Thessaloniki, Greece; Papadimitriou, E.; Geophysics Department, School of Geology, Aristotle University of Thessaloniki, Greece; Vallianatos, F.; Technological Educational Institute of Crete, Department of Natural Resources & Environment, Geophysics & Seismology Laboratory, Crete, Greece Abstract: A strong (Mw=6.7) intermediate depth earthquake occurred on 8 January 2006 (11:34 UTC) in southwestern Aegean Sea (Greece) causing limited damage to structures on the nearby islands of Kythira and Antikythira, as well as western Crete Island. The epicentral area belongs to the SW segment of the Hellenic Arc, which is known to be associated with the occurrence of large shallow and intermediate depth earthquakes, mainly due to the subduction of the Eastern Mediterranean oceanic lithosphere under the Aegean microplate. The main shock occurred on a dextral strike slip fault at a depth of 75 km, within the descending slab, as it is revealed by both, the spatial distribution of the accurately located aftershocks and its fault plane solution determined in the present study and implying a slab-pull event. The aftershock activity from 8 to 31 January 2006 is distributed in depths ranging from 55 to 75 km, and being comprised in an almost rectangular and vertical plane with a length equal to 28 km and a width of 20 km, which adequately defines the dimensions of the rupture area. The geometry of the Wadati-Benioff zone in this area, namely the southwestern part of the Hellenic Arc, is explored by an exhaustive analysis of all the available phase arrivals gathered from the International Seismological Centre, and the relocation of the earthquakes occurred since 1964 in the South-West Aegean region.

Relation between electric properties and water saturation for hematitic sandstone with frequency

Tue, 30 Sep 2008 22:00:00 GMT

Title: Relation between electric properties and water saturation for hematitic sandstone with frequency Authors: Gomaa, M. M.; National Research Centre, Geophysical Sciences Dep., El-Tahrir St. Dokki, 12311, Egypt Abstract: This paper focuses on the effect of water saturation on A. C. electrical conductivity and dielectric constant of fully and partially saturated hematitic sandstone sample (Aswan area, Egypt). The saturation of the sample was changed from partial to full saturation. Complex resistivity measurements at room temperature (~16°C), were performed in the frequency range from 0.1 Hz to 100 KHz. Experimental electrical spectra indicate, generally, that the electrical conductivity and dielectric constant vary strongly with water saturations and frequency. The low frequency electrical conductivity and dielectric constant are mainly controlled by surface conduction and polarization of the electrical double layer. The behaviour of the electrical conductivity and dielectric constant, with increasing water content, were argued to the orientational polarization of bound water for very low saturations, displacement of the excess surface charges for relatively low saturations, and free exchange of excess ions in double layer with the bulk electrolyte and generation of transient diffusion potentials which lag behind the applied field for high saturations.

Using neural networks to study the geomagnetic field evolution

Tue, 30 Sep 2008 22:00:00 GMT

Title: Using neural networks to study the geomagnetic field evolution Authors: Duka, B.; Department of Physics, Faculty of Natural Sciences, University of Tirana; Hyka, N.; Department of Physics, Faculty of Natural Sciences, University of Tirana Abstract: study their time evolution in years. In order to find the best NN for the time predictions, we tested many different kinds of NN and different ways of their training, when the inputs and targets are long annual time series of synthetic geomagnetic field values. The found NN was used to predict the values of the annual means of the geomagnetic field components beyond the time registration periods of a Geomagnetic Observatory. In order to predict a time evolution of the global field over the Earth, we considered annual means of 105 Geomagnetic Observatories, chosen to have more than 30 years registration (1960.5-2005.5) and to be well distributed over the Earth. Using the NN technique, we created 137 «virtual geomagnetic observatories» in the places where real Geomagnetic Observatories are missing. Then, using NN, we predicted the time evolution of the three components of the global geomagnetic field beyond 2005.5.

Variations in geoacoustic emissions in a deep borehole and its correlation with seismicity

Tue, 30 Sep 2008 22:00:00 GMT

Title: Variations in geoacoustic emissions in a deep borehole and its correlation with seismicity Authors: Gavrilov, V.; Institute of Volcanology and Seismology, Far East Branch of the Russian Academy of Science, Petropavlovsk-Kamchatsky, Russia; Bogomolov, L.; Institute of Marine Geology and Geophysics Far East Branch, of the Russian Academy of Science, Yuzhno-Sakhalinsk, Russia; Morozova, Y.; Institute of Volcanology and Seismology, Far East Branch of the Russian Academy of Science, Petropavlovsk-Kamchatsky, Russia; Storcheus, A.; Institute of Volcanology and Seismology, Far East Branch of the Russian Academy of Science, Petropavlovsk-Kamchatsky, Russia Abstract: Continuous geoacoustic emission (GAE) measurements were acquired using a three-component geophone placed in a borehole at a depth of near 1000 m at Petropavlovsk-Kamchatsky starting in August 2000. Using geophones consisting of magneto-elastic crystal ferromagnetic sensors, and installed at such a depth allows measurement of natural geoacoustic background with signal amplitude less than 1×10-4 m/s3 in frequency band from 3 to 1500 Hz. According to the data from a 4-year survey period the characteristics of diurnal geoacoustic variations change before every earthquake with MLH≥ 5.0 that occurs at a distance of less than 300 km from the observation point or before each earthquake with MLH≥5.5 occurring at distance R≤550 km from the observation point. The changes in GAE regime correlate with the strongest earthquakes that occurred during survey period. Measurements of the natural electromagnetic field of the Earth were carried out simultaneously with the help of an underground electric antenna. The behavior of GAE in aseismic periods appears to be related to the effect of diurnal variations of the natural electromagnetic field.