http://hdl.handle.net/2122/232 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5832 Titolo: Three years continuous record of the Earth's magnetic field at Concordia Station (DomeC, Antarctica)<br/><br/>Autori: Chambodut, A.; EOST, France; Di Mauro, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Schott, J.-J.; EOST, France; Bordais, P.; IPEV, France; Agnoletto, L.; ENEA, Italy; Di Felice, P.; ENEA, Italy<br/><br/>Abstract: The magnetic observatory deployed at DomeC, Antarctica, in the French-Italian base known as Concordia has now been permanently running for more than three years. This paper focuses on these long-term results which are more relevant for an observatory intended to provide absolute values of the field. The problems which emerged in this fairly long record are discussed and solutions suggested to upgrade the observatory to the standards of an absolute one (i.e. Intermagnet standards). http://hdl.handle.net/2122/5167 Titolo: Geomagnetic jerks in the polar regions<br/><br/>Autori: Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: The occurrence of geomagnetic jerks over the Arctic and Antarctic regions is here investigated. Maps of geomagnetic secular acceleration over the polar regions are produced from the CM4 and CHAOS models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration. The obtained results confirm that in Antarctica geomagnetic jerks systematically follow geomagnetic jerks in the Arctic region with a time delayfrom one to three years. Evidence is found of an abrupt change in secular acceleration in both polar regions around 1985, suggesting that the 1985 local jerk could actually be a worldwide event. Combining our results with the results previously obtained on the occurrence of a geomagnetic jerkat low-mid latitudes around 2003, we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century. http://hdl.handle.net/2122/4561 Titolo: Magnetic structural evidences of the 41° parallel zone (Tyrrhenian Sea) inferred from potential field data: the 3D model of the discontinuity<br/><br/>Autori: Cocchi, L.<br/><br/>Abstract: Potential field data hold a leading role in the geologic-structural application. Their use becomes even more important if appliedto extremely inaccessible zones as oceanic basins or no-antropized area. By anareo-naval survey it is possible to cover large areas, in a short time, to define their deep crustal features that are otherwise not accessibleby other direct methods. The analysis of the magnetic field data is particularlyeffective in the study of the crustal portions characterized by lateral variation of the magnetic susceptibility. The magnetic analysis is often applied to areas where sub-volcanic bodies or relic portion of oceanic nature in sedimentary deposits are located. The aim of this thesis is the development of a tridimensional model aboutthe 41st parallel zone starting from potential field data.The name 41st parallel indicates a geographic zone aligned alongN41st of latitude. This area is longitudinally defined between theContinental Campanian Margin (Naplean Gulf, Ischia and Procida island) andthe northwestern portion of the Sardinia Island.From a geological point of view, the 41st parallel represents acomplicate area. Several geological structures are located along this zone: submerged volcanic bodies such as the Etruschi,Vercelli and Cassinis seamounts, emerged edifices connected to thePliocenic-Quaternary volcanism of the Central Tyrrhenian sea (Palmarola,Zenone, Ponza, Ischia and Procida) and several deep fault structures such as the E-W fault of Ponza.The formation and the development of this particular zone is not clear andis still object of discussion in literature. The structural setting of 41st parallel zone is highlighted only by magnetic field data. By theobservation of the magnetic anomalous field it is possible to see analignment of several magnetic anomalies along the N41st latitude.These anomalies take place on the main structural evidences of the area.The bathymetric data and information don't suggestthese features. To this aim, I use the magnetic data to analyse in quantitativeway, the 41st parallel zone.The magnetic data used for the development of the 3D magnetic model derived bythe dataset of the Aeromagnetic Anomaly Map of Italy (Caratori Tontini et al., 2004). The original magnetic dataset includes the total intensity field of Italy and its surrounding seas acquired partly during the aeromagneticsurveys performed by Agip (now Eni-Spa) between 1971 and 1980 and during new surveys in the years 2001-2002(Eni,Exploration & Production Division - Igmar, La Spezia). The magnetic data were recorded, in a homogeneous way, by using a cesium-magnetometer. By the successive reprocessing of the row magnetic datathe revised magnetic anomaly map is obtained showing a strong informative contribution and a good agreement with the sea-level map of Chiappini et al. (2002).In the first chapter of this thesis I describe the geological and structuralfeatures of the Tyrrhenian sea in general way. However, I analyse the 41st parallel zone starting from the literature data. In the second chapter I evaluate the Bouguer gravity field of the Tyrrhenian Sea by usingtwo methodologies for an evaluation of the optimal Bouguer reduction density. Using a free-air gravimetric satellite data set of the Tyrrhenian sea, I perform a map of isostatic level of the central Tyrrhenian area. In the thirdchapter I describe the properties of the Geomagnetic field and its representation focusing my interest on the time and spatial dependencies of the field. The successive section provides information about the row magnetic data used for the quantitative elaboration describing the characteristics of the anomaly field of the studied area. In the fifth chapter, the properties of the magnetic signal is studied by using a statistical analysis of the power spectrum (Spector and Grant, 1970) and by the Continuous Wavelet Transform. After these analyses, in the sixth chapter I introduce the concept of magnetic basement and the relationship between magnetic signal and temperature. Starting fromthe regional heat-flow data (Della Vedova et al., 2001) of the Central Tyrrhenian area the Curie Isotherm surface is modeled defining themaximum depth of the magnetic-thermal basement. The boundaries of the magnetic sources (top and bottom) represents the base-line for the successive phases of quantitative analysis.By using a 2D inversion algorithm I obtainthe map of apparent susceptibility. In the seventh chapter, I apply this algorithm to the magnetic evidence of the 41st parallel zone and to the Selli Line region. This procedure suggests a distribution of magnetization that permits to connect the 41st parallel zone and the structural elements of the Southern Tyrrhenian Sea such as the Magnaghi Basin and the Selli Line faults system.Starting form the results obtained by the apparent magnetization maps, I perform a 3D inversion of magnetic data providing information about the vertical distribution of the sources. In the eighth chapter, that represents an important part of the thesis, I introduce the inverse problem in the potential field analysis by a new 3D algorithm capable to evaluate the depth to the bottom of the source. Then, I apply this algorithm to the real magnetic dataset of the 41st and Selli Line regions. The recovered models show the shape, location in depth and direction of developmentof the magnetic generating sources suggesting the geometric relationship between the different sources. These information are important for evaluatingthe crustal setting of the study area. Finally, in the lastchapter I interpret the results of inversion process evaluating the relationship between the 41 st parallel and the Selli Line region. Starting from the magnetic recovered modelsof these two regions I provide a chronological reconstruction of the geodynamicevolution of the Central Tyrrhenian Sea. http://hdl.handle.net/2122/4418 Titolo: Three years continuous record of the Earth's magnetic field at Concordia station (DomeC, Antarctica)<br/><br/>Autori: Chambodut, A.; EOST, Strasburg, France; Di Mauro, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Schott, J.-J.; EOST, Strasburg, France; Bordais, P.; IPEV, France; Agnoletto, L.; Enea, Italia; Di Felice, P.; Enea, Italia<br/><br/>Abstract: The magnetic observatory deployed at DomeC, Antarctica, in the French-Italian base known as Concordia base, is now permanently running for more than three years. This paper focuses on these long-term results which are more relevant for an observatory intended to provide absolute values of the field. The problems which came up in the light of this fairly long record are discussed and solutions suggested in order to upgrade the observatory to the standards of an absolute one (i.e. Intermagnet standards). http://hdl.handle.net/2122/3977 Titolo: A simple approach to the transformation of spherical harmonic models under coordinate system rotation<br/><br/>Autori: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l'Ebre, CSIC, 43520 Roquetes, (Tarragona), Spain; Falcone, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: The transformation of a set of spherical harmonic coefficients characterizing a modelof the geomagnetic field, or a general function defined on a sphere, subject to a rotation of the coordinate system, is given by the direct relations between the coefficients and then by using a numerical approach. The parameters for a pair of such rotations (from one set to another, and vice versa) are given, along with a few examples of their application. The method is particularly useful for the comparison of geophysical characteristics derived from models developed under different coordinate systems. It offers a practical solution to the problem, which can be implemented without difficulty. http://hdl.handle.net/2122/3976 Titolo: Translated origin spherical cap harmonic analysis<br/><br/>Autori: De Santis, A.; Istituto Nazionale di Geofisica, Roma, Italia<br/><br/>Abstract: The method of spherical cap harmonic analysis (SCHA), due to Haines (1985) is appropriate for regional geomagnetic field modelling as it includes the required potential field constraints and, for a given number of model parameters, describes shorter wavelength features than a global spherical harmonic model. If the origin of the coordinate system is moved from the centre of the Earth towards the surface then the Earth's surface is no longer equidistant from the origin. At the Earth's surface the minimum wavelength described by a SCH model in the new coordinate system is smaller at the centre of the region than at the edge. This method oftranslated origin spherical cap harmonic analysis (TOSCA) has been applied to regional field modelling for Italy. The method is able to take advantage of the dense distribution of data at the centre of region and the model effectively smooths towards the periphery. The performance of the TOSCA model is discussed in relation to a model derived using conventional SCHA. http://hdl.handle.net/2122/3975 Titolo: Simple additional constraints on regional models of the geomagnetic secular variation field<br/><br/>Autori: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Falcone, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Torta, J. M.; Observatori de I'Ehre, Consejo Superior de Investigationes Cientificas (CSIC), 43520 Roquetes (Tarragona), Spain<br/><br/>Abstract: Standard ways of building regional models of the geomagnetic field fail when one wishes to model secular variation (SV). The reason for this is that the SV is mainly a large-scale feature, while regional modelling is most appropriate for characterizing small-scale features. The new idea presented in this note consists in reducing this effect by requiring that the spatial derivatives of the SV produced by the regional model fit the values given by global (and smoother) models such asthe international geomagnetic reference field.<br/><br/>Descrizione: Lecter section of Physics of the Earth and Planetary Interiors 97 (1996) http://hdl.handle.net/2122/3970 Titolo: The first Antarctic geomagnetic Reference Model (ARM)<br/><br/>Autori: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l'Ebre, Roquetes, Spain; Gaya-Piqué, L. R.; Observatori de l'Ebre, Roquetes, Spain<br/><br/>Abstract: Spherical Cap Harmonic Analysis has been applied to obtain a reference model of geomagnetic secular change for Antarctica valid for the last forty years. In this paper, we use the latest availableobservatory data to update this model and to compare it with the 8th generation IGRF. In addition, the selected set of total field values used for the generation of the Oersted Initial Field Model have been employed together with observatory data to develop the first complete Antarctic Reference Model (ARM). This model improves the fit to the secular variation deduced from observatory data by about 60% relative to IGRF, and the fit to observatory and satellite field data by 8%. The model allows merging data sets taken at different altitudes and epochs in Antarctica, where significant temporal geomagnetic variations occur. http://hdl.handle.net/2122/3965 Titolo: Spherical Cap Harmonics Revisited and their Relationship to Ordinary Spherical Harmonics<br/><br/>Autori: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l'Ebre, CSIC, 43520 Roquetes, Tarragona, Spain; Lowes, F. J.; Physics Department, University of Newcastle Upon Tyne, NE1 7RU, U.K.<br/><br/>Abstract: The "global" representation of the geomagnetic field in terms of ordinary spherical harmonics (SHs) and its corresponding set {g,h} of coefficients has been studied extensively, but the "local" representation in terms of spherical cap harmonics (SCHs) and its corresponding set{G,H} of coefficients is not yet well understood. This paper clarifies some of the main properties of the SCHs and their proper use along with their relationship with the SHs. In particular, it shows that for the spherical cap part of a global field specified by spherical harmonics there is astrict relation between the ordinary Legendre functions of the global representation and the fractional functions of the local expansion; hence we can express the set ofcoefficients {G,H} in terms of the set {g,h}. Finally, some attention will be given to the role of the leading (n=0, m=0) term of the SCH expansion. http://hdl.handle.net/2122/3961 Titolo: New model alternatives for improving the representation of the core magnetic field of Antarctica<br/><br/>Autori: Gaya-Piqué, L. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ravat, D.; Department of Geology 4324, Southern Illinois University Carbondale, Carbondale, IL 62901-4324, USA; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l’Ebre, CSIC - URL, Horta Alta 38, 43520 Roquetes, Spain<br/><br/>Abstract: Use of the International Geomagnetic Reference Field Model (IGRF) to construct magnetic anomaly maps can lead to problems with the accurate determination of magnetic anomalies that are readily apparent at the edges of local or regional magnetic surveys carried out at different epochs. The situation is severe in areas like Antarctica, where ionospheric activity is intense and only a few ground magnetic observatories exist. This makes it difficult to properly separate from ionospheric variations the secular variation of the core magnetic field. We examine two alternatives to the piecewise-continuous IGRF core magnetic field in Antarctica for the last 45 years: the present global Comprehensive Model (CM4) and the new version of the Antarctic Reference Model (ARM). Both these continuous models are better at representing the secular variation in Antarctica than the IGRF. Therefore, their use is recommended for defining the crustal magnetic field of Antarctica (e.g. the next generation of the Antarctic Digital MagneticAnomaly Map).