http://hdl.handle.net/2122/200 2013-05-25T17:47:01Z http://hdl.handle.net/2122/8671 Title: Possible model of electromagnetic signals before earthquakes Authors: Dudkin, F.; Lviv Centre of Institute for Space Research, Ukraine; Korepanov, V.; Lviv Centre of Institute for Space Research, Ukraine; Hayakawa, M.; University of Electro-Communications, Japan; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Few days before many earthquakes a general change in the ratio of vertical to horizontal magnetic field components in the ULF band, often called “polarization”, has been observed that can be considered as a magnetic precursor of the subsequent earthquake. To explain such a specific behavior, we propose a simple model based on a linear current approximation depending on some assumption on the signal to noise ratio. This model is confirmed through a comparison that has been carried out between the experimental magnetic field data at Matsushiro (Japan, 1998.06.30, M=4.7) and Simeiz (Crimea, Ukraine, 1998.10.16, M=4.3 and 1998.10.18, M=4.3) earthquakes. About 1 – 2 days before these events we had recorded the anomalous decrease of the ratio of vertical to horizontal magnetic field components in Pc4 – Pc3 band. The NE-SW direction of the corresponding current linear model well agrees with the main tectonic feature of both seismogenic events. Additionally we also estimate the signal to noise ratio limits for the detection of ULF magnetic field components in Corralitos and Stanford campus for Loma Prieta (MS 7.1, 1989) earthquake. 2012-12-31T23:00:00Z http://hdl.handle.net/2122/8669 Title: Curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central Aeolian Ridge (Southern Tyrrhenian Sea, Italy) Authors: De Ritis, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ravat, D.; Department of Earth and Environmental Sciences, University of Kentucky; Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Salina, Lipari, and Vulcano volcanic ridge and the surrounding sea sectors (Aeolian Archipelago, Southern Tyrrhenian Sea, Italy) are characterized by vents responsible for a recent (<40 ka—1889/1890 AD) effusive and explosive subareal activity and repeated, 56 to 7 ka in age, submarine explosive eruptions from source areas located between Lipari and Vulcano. A spectral depth estimation of the magnetic bottom using a fractal method on aeromagnetic data from Vulcano, Lipari, and Salina volcanic ridge allows us to constrain the Curie isotherm depth. The elevated portion of the isotherm is between 2 and 3 km below Salina and Vulcano and about 1 km below Lipari. The Curie depth results in the context of other geological and geophysical evidence suggest that the rise of the Curie isotherm is mainly due to the occurrence of shallow heat sources such as magma ponds and associated hydrothermal systems. The short-wavelength magnetic anomaly field reflects magnetic contrasts from highly magnetized volcanic bodies, low-magnetization sediments, and hydrothermally altered rocks. Borehole temperature data verify the Curie temperature derived from the magnetic methods on the island of Vulcano.We conclude that the whole Vulcano, Lipari, and Salina volcanic ridge is active and should be monitored. 2013-03-19T23:00:00Z http://hdl.handle.net/2122/8614 Title: Magnetic transfer function entropy and the 2009 Mw = 6.3 L’Aquila earthquake (Central Italy) Authors: Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Barraclough, D. R.; British Geological Survey, Edinburgh, UK; Wu, L. X.; Academy of Disaster Reduction and Emergency Management, Beijing Normal University, China; Qin, K.; China University of Mining and Technology, Beijing, China Abstract: With the aim of obtaining a deeper knowledge of the physical phenomena associated with the 2009 L’Aquila (Central Italy) seismic sequence, culminating with a Mw = 6.3 earthquake on 6 April 2009, and possibly of identifying some kind of earthquake-related magnetic or geoelectric anomaly, we analyse the geomagnetic field components measured at the magnetic observatory of L’Aquila and their variations in time. In particular, trends of magnetic transfer functions in the years 2006–2010 are inspected. They are calculated from the horizontal to vertical magnetic component ratio in the frequency domain, and are very sensitive to deep and lateral geoelectric characteristics of the measurement site. Entropy analysis, carried out from the transfer functions with the so called transfer function entropy, points out clear temporal burst regimes of a few distinct harmonics preceding the main shock of the seismic sequence. A possible explanation is that they could be related to deep fluid migrations and/or to variations in the micro-/meso-fracturing that affected significantly the conductivity (ordered/disordered) distribution in a large lithospheric volume under the seismogenic layer below L’Aquila area. This interpretation is also supported by the analysis of hypocentres depths before the main shock occurrence. 2012-07-22T22:00:00Z http://hdl.handle.net/2122/8072 Title: Flank instability structure of Mt. Etna inferred by a magnetotelluric survey Authors: Siniscalchi, A.; Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Bari, Italy; Tripaldi, S.; Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Bari, Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Balasco, M.; Istituto di Metodologie per l’Analisi Ambientale, Consiglio Nazionale delle Ricerche, Tito, Potenza, Italy; Romano, G.; Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Bari, Italy; Ruch, J.; Dipartimento di Scienze Geologiche, Università di Roma Tre, Rome, Italy; Schiavone, D.; Dipartimento di Scienze Geologiche, Università di Roma Tre, Rome, Italy Abstract: This paper presents a magnetotelluric (MT) survey of the unstable eastern flank of Mt. Etna. We take thirty soundings along two profiles oriented in the N-S and NW-SE directions, and from these data recover two 2D resistivity models of the subsurface. Both models reveal three major layers in a resistive-conductive-resistive sequence, the deepest extending to 14 km bsl. The shallow layer corresponds to the volcanic cover, and the intermediate conductive layer corresponds to underlying sediments segmented by faults. These two electrical units are cut by E-W-striking faults. The third layer (basement) is interpreted as mainly pertinent to the Apennine-Maghrebian Chain associated with SW-NE-striking regional faults. The detailed shapes of the resistivity profiles clearly show that the NE Rift is shallow-rooted ( 0–1 km bsl), thus presumably fed by lateral dikes from the central volcano conduit. The NW-SE profile suggests by a series of listric faults reaching up to 3 km bsl, then becoming almost horizontal. Toward the SE, the resistive basement dramatically dips (from 3 km to 10 km bsl), in correspondence with the Timpe Fault System. Several high-conductivity zones close to the main faults suggest the presence of hydrothermal activity and fluid circulation that could enhance flank instability. Our results provide new findings about the geometry of the unstable Etna flank and its relation to faults and subsurface structures. 2012-03-29T22:00:00Z http://hdl.handle.net/2122/7173 Title: Ground Penetrating Radar Survey Inside the S. Agata Cathedral of Catania (Eastern Sicily) Authors: Imposa, S.; Università degli Studi di Catania, Catania, Italy; Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: This article presents the results of a ground penetrating radar survey carried out in 2003 inside the S. Agata Cathedral of Catania (eastern Sicily). The aim was to reconstruct the subsurface conditions of the central nave floor to assess the load-bearing capacity of the vauable pavement in view of restoration interventions. Data was acquired with a multi-antenna array along a grid of transversal and longitudinal profiles, for a total length of approximately 700 m. Georadar images of the subsoil were used to locate anomalies probably associated with crypts, some of them unknown before the present study, and strengthening elements beneath the pavement. A three-dimensional model of the subsoil in a portion of the study area has been obtained from the interpretation of the ground penetrating radar images. 2010-12-31T23:00:00Z http://hdl.handle.net/2122/7163 Title: Non-inductive components of electromagnetic signals associated with L’Aquila earthquake sequences estimated by means of inter-station impulse response functions Authors: Di Lorenzo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Palangio, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Santarato, G.; Universit`a degli Studi di Ferrara, Italy; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Villante, U.; Universit`a degli studi di L’Aquila, Italy; Santarelli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: On 6 April 2009 at 01:32:39 UT a strong earthquake occurred west of L’Aquila at the very shallow depth of 9 km. The main shock local magnitude was Ml = 5.8 (Mw=6.3). Several powerful aftershocks occurred the following days. The epicentre of the main shock occurred 6 km away from the Geomagnetic Observatory of L’Aquila, on a fault 15 km long having a NW-SE strike, about 140 , and a SW dip of about 42 . For this reason, L’Aquila seismic events offered very favourable conditions to detect possible electromagnetic emissions related to the earthquake. The data used in this work come from the permanent geomagnetic Observatories of L’Aquila and Duronia. Here the results concerning the analysis of the residual magnetic field estimated by means of the inter-station impulse response functions in the frequency band from 0.3 Hz to 3 Hz are shown. 2011-04-05T22:00:00Z http://hdl.handle.net/2122/7156 Title: First Field Magnetometer Investigation at the Phoenician Island of Mozia (Trapani), Northwestern Sicily: Preliminary Results Authors: Di Mauro, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sapia, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Nigro, L.; Univ. Sapienza; Marchetti, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The island of Mozia represents a unique location for geophysical investigations applied to archaeological research. The presence of exposed structures and ongoing studies, run by the University ‘La Sapienza’ of Rome, allows a direct comparison of geophysical exploration data with the excavations results, giving an immediate control on the accuracy and robustness of the geophysical survey conducted. Four areas around the Kothon, a Phoenician artificial basin, have been investigated by means of magnetic methods; the purpose was to trace a semi-circular wall surrounding the structure of the basin. The geophysical results confirmed the presence of the wall, as postulated by the archaeological study, and indicated magnetic anomalies associated with previously unknown structures. Subsequent archaeological excavation confirmed these latter data. The magnetic signature of the topsoils and remains characterizing the area surveyed,was undoubtedly weak, even though the resulting anomalies maps were adequately clear and allowed the characterization of the archaeological structures in the area. Field and laboratory magnetic susceptibility measurements allowed better understanding of the data. The study confirmed that geomagnetic investigations can be used in weakly magnetic susceptibility environments, as in Mozia, and are productive if conducted in accordance with an archaeological agenda. Copyright © 2011 John Wiley & Sons, Ltd. 2011-07-27T22:00:00Z http://hdl.handle.net/2122/6982 Title: Integrated geophysical measurements on a test site for detection of buried steel drums Authors: Marchetti, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Geophysical methods are increasingly used to detect and locate illegal waste disposal and buried toxic steel drums. This study describes the results of a test carried out in clayey-sandy ground where 12 empty steel drums had previously been buried at 4-5 m below ground level. This test was carried out with three geophysical methods for steel-drum detection: a magnetometric survey, electrical resistivity tomography with different arrays, and a multifrequency frequency-domain electromagnetic induction survey. The data show that as partially expected, the magnetometric and electromagnetic induction surveys detected the actual steel drums buried in the subsurface, while the electrical resistivity tomography mainly detected the changes in some of the physical properties of the terrain connected with the digging operations, rather than the actual presence of the steel drums. 2011-04-25T22:00:00Z http://hdl.handle.net/2122/6735 Title: Definizione delle strutturetettoniche nell’area aquilana mediante interpretazione 3D didati gravimetrici con un algoritmo basato sull’accrescimento dei corpi. Risultati preliminari. Authors: Berrino, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; CAMACHO, A.G.; Instituto de Astronomía y Geodesia (CSIC-UCM), Madrid (Spain); BELLUCCI SESSA, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia Abstract: -L’interpretazione tridimensionale èstata effettuata mediante l’utilizzo di un programma di calcolo basato su un algoritmo denominato “GROWTH”realizzato presso l’istituto de Astronomia y Geodesia della Facoltàdi Matematica dell’UniversitàComplutense di Madrid (Camachoetal., 2000) -Il metodo si basa sulla determinazione del volume di corpi profondi e lavora per iterazione su corpi prismatici il cui volume viene “accresciuto”in modo automatico al fine di ottenere il migliore “fitting”con i dati osservati -Il vantaggio di tale algoritmo, oltre all’automatismo e alla semplicità di utilizzo, è che esso non prevede un modello di innesco preventivamente costruito, può risolvere il modello utilizzando contemporaneamente contrasti di densità sia positivi che negativi e fornire, tra le altre informazioni, l’andamento regionale delle anomalie di Bouguer, necessario per la definizione delle strutture crostali più profonde 2009-12-31T23:00:00Z http://hdl.handle.net/2122/6692 Title: Repeat Station Activities Authors: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Barraclough, D. R.; Geomagnetism Research Group, British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, Gt. Britain Editors: Mandea, M.; Helmholtz Centre Potsdam, Deutsches GeoForschungsZentrum (GFZ), Sektion 2.3 Erdmagnetfeld, Potsdam, Germany; Korte, M.; Helmholtz Centre Potsdam, Deutsches GeoForschungsZentrum (GFZ), Sektion 2.3 Erdmagnetfeld, Potsdam, Germany Abstract: A repeat station is a site whose position is AQ1 accurately known and where accurate measurements of the geomagnetic field vector are made at regular intervals in order to provide information about the secular variation of the geomagnetic field. In this chapter we begin by giving a brief history of the development of repeat station networks. We then describe the instruments used to make measurements at a repeat station. These include fixing the position of the station, finding the direction of true north and measuring the components of the geomagnetic field. Emphasis is given to techniques and instruments that are in current use. We next discuss the procedures that are used to reduce the measurements to a usable form and consider the uses to which the reduced data are put. Finally, we discuss the continued importance of such data in the present era of satellite geomagnetic surveys. 2009-12-31T23:00:00Z