ALBERT

Description: Seafloor clearance methods based on acoustic, direct-inspection, and single-sensor magnetic approaches suffer from limitations in controlling the target-sensor distance, and may prove ineffective when the small size or the dangerous nature of targets requires high accuracy in localization. Moreover, random magnetic variations over time bring about spatial decorrelation phenomena, and hinder the application of double-sensor methods in noisy harbour environments. The new High Definition (HD) magnetic survey protocol tackles the measurement-distance problem in two ways: first, by varying the sensor depth dynamically, and secondly by backprojecting the measured field according to seafloor data and vertical incremental factors associated with the bandwidth characteristics of targets. The method to make up for timeinduced loss in spatial localization ability exploits the local behaviour of a coherence function, which correlates local observations to a set of spatially-stabilized reference stations. The consequent normalization of measured magnetic signals allows one to assign the monitored areas with a specific level of confidence in the detection results, ranging from 100% (certainty) to 0% (random events). The principles of HD detection have been fully applied in the seafloor clearance of the firing test site located south of Cape Teulada (Sardinia, Italy), where very weak signal sources such as cartridge cases, mines, and small objects down to 1 Kg mass values (lobster pots) have been successfully localized, even when covered by extensive colonies of Posidonia.

Description: Published

Description: Stockolm, Sweden

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: We are reporting some results and future planning of the Magnetic and Electric fields Monitoring Project. The principal purpose of the project is to create a network of observatories for monitoring the electromagnetic signals in the 0.001 Hz–100 kHz frequency bands in Central Italy. These bands include both natural and artificial signals. The technological objectives of the project are the development of new instrumentation and the know-how transfer to the industry. These instruments were tested in the Geomagnetic Observatory of L’Aquila, the first station of the network. Here we show some examples of the developed electric and magnetic sensors. These instruments are designed for the automatic long-term recording of the electromagnetic fields in a wide band of frequency. The preliminary results of the first operating station of the network are shown taking into account, in the signal elaboration, the single station approach. Here we are reporting some examples concerning the calculation of the ground electric resistivity profile, the evaluation of the magnetic induction vectors and the study of the magnetic sources by the eigenvectors calculation. When all the stations of the network will be in operation, the use of an innovative technique, the wideband interferometry will be proposed. Combining the simultaneous observations of the electromagnetic field measured in each station, we will be able to obtain detailed information about the investigated electromagnetic sources.

Description: Published

Description: 729 - 737

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: JCR Journal

Description: reserved

Description: In order to obtain a preliminary overview on the effectiveness of the underwater anti-divers magnetic-acoustic “MAC System”, we have developed a synthesis between the results coming out from the two different subsystems (magnetic and acoustic), based on two different models, during two different test sections. The section covered by the magnetic component, measured near the NURC dock (La Spezia, Italy) in very noisy port condition, has been remodeled on the sea bottom profile of the access channel to the Italian Navy Base in La Spezia, which presents environmental electromagnetic noise compatible with the NURC’s one. In this entrance way has been executed an acoustic port protection experiment, too. The two different covered sections (magnetic and acoustic) have been merged to obtain an integrated synthetic model of the accuracy of the MAC System. The results have pointed out a remarkable increase of the antidivers covering effectiveness, in particular in the boundary zone of the access way to be protected: the confidence of the MAC System can be considered quite 1 and higher in respect to the sum of the confidence of the two subsystems.

Description: Published

Description: Cannes, France

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: People who attend to the problem of underwater port protection usually use sonar based systems. Recently it has been shown that integrating a sonar system with an auxiliary array of magnetic sensors can improve the effectiveness of the intruder detection system. One of the major issues that arise from the integrated magnetic and acoustic system is the interpretation of the magnetic signals coming from the sensors. In this paper a machine learning approach is proposed for the detection of divers or, in general, of underwater magnetic sources. The research proposed here, by means of a windowing of the signals, uses Support Vector Machines for classification, as tool for the detection problem. Empirical results show the effectiveness of the method.

Description: Published

Description: 37-44

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: From 2000 to 2005 two geophysical exploration missions were undertaken in the Tyrrhenian deep seafloor at depths between -2000 and -3000 m in the framework of the European-funded GEOSTAR Projects. The considered missions in this work are GEOSTAR-2 and ORION-GEOSTAR-3 with the main scientific objective of investigating the deep-seafloor by means of an automatic multiparameter benthic observatory station working continuously from around 5 to 12 months each time. During the two GEOSTAR deep seafloor missions, scalar and vector magnetometers acquired useful magnetic data both to improve global and regional geomagnetic reference models and to infer specific geoelectric information about the two sites of magnetic measurements by means of a forward modelling.

Description: Published

Description: 57-63

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: open

Description: Inversion of new high-resolution magnetic data from the Marsili seamount and the surrounding basin in the Tyrrhenian Sea reveals NNE–SSW magnetization stripes ranging from the Matuyama chron to the Brunhes chron, including the short positive Jaramillo subchron. The detailed magnetic chronology shows that from the late Matuyama (1.77 Ma), the average half spreading rate was about 1.5 cm yr-1, with a slight decrease between the Jaramillo and the Brunhes events, when the growth of the volcanic edifice overcame lateral spreading. Analysis of spreading rate and volume of erupted lava indicates that at the beginning of the Jaramillo subchron (1.07 Ma), the Marsili basin evolved from pure horizontal spreading to a superinflated seamount as a consequence of tearing of the Ionian slab. Our data give us a snapshot of the geodynamic transition from an active backarc spreading phase to the vertical accretion of the seafloor because of a radical change in the subduction dynamics.

Description: Published

Description: 369-374

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: JCR Journal

Description: reserved

Description: We show a set of forward model equations in the Fourier domain for calculating the 3-D gravity and magnetic anomalies of a given 3-D distribution of density or magnetization. One property of the potential field equations is that they are given by convolution products, providing a very simple analytic expression in the Fourier domain. Under this assumption, the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space, and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions. A very fine spatial discretization can be obtained by using a large number of points within a unique 3-D grid, where both the source distributions and field data are defined. The main advantage of this formulation is that it dramatically reduces execution times, providing a very fast forward model tool useful for modeling anomalies at different altitudes. We use this method to evaluate an average magnetization of 8 A/m for the Palinuro Seamount in the Tyrrhenian Sea (southern Italy), thus performing a joint interpretation of morphological and newly acquired magnetic data.

Description: Published

Description: B02103

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: JCR Journal

Description: reserved

Description: We show the magnetic model of the Selli-Vavilov region. The Selli Line is known as the northwestern edge of the southern Tyrrhenian basin. The tectonic evolution of the Tyrrhenian basin is dominated by a Tortonian - Quaternary extension through the eastward movement of the Apennine subduction system. This migration has generated a diffuse stretching of the continental crust with the emplacement of new oceanic material. This latter occurred in several localized zones where the eastward retreating of the Ionian subduction system produced a strong depletion of the crust with formation of basins and correlated spreading. Nowadays the presence of oceanic crust is confirmed through direct drilling investigation but a complete mapping of the oceanic crustal distribution is still lacking. The Selli-Vavilov region shows a differentiated crustal setting where seamount structures, the oceanic basement portions and continental crust blocks are superimposed. To this aim, a 2D inversion of the magnetic data of this region was conducted to define buried structures. The magnetic susceptibility pattern was computed by solving the least squares problem of the misfit between the predicted and real data for separated wavebands. This method produced two 2D models of the high and low frequency fields of the Selli-Vavilov region. The two apparent susceptibility maps provide different information for distinct ranges of depth. The results of the inversions were also combined with seismic data of the Selli region highlighting the position of the highly-magnetized buried bodies. The results confirm a role for the Selli Line as a deep crustal boundary dividing the Sardinian passive domain from the easternmost active region where different oceanic structures are located. The Selli Line has worked as a detachment fault system which has moved eastward. Finally, the Selli-Vavilov region may be interpreted as a tectonic result due to a passive asymmetrical rift occurred between the Tortonian and Pliocene.

Description: Published

Description: 251-266

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: 3.4. Geomagnetismo

Description: 3.5. Geologia e storia dei sistemi vulcanici

Description: JCR Journal

Description: reserved

Description: A scientific debate has developed in the last few years as to whether a 130 m diameter sag pond surrounded by a saddle-shaped rim and neighboring smaller sags from the Sirente Plain (Abruzzi, Italy) represent the only known Italian meteoritic crater field, a mud volcano, or an anthropogenic feature. To decipher the nature of the Sirente landforms, we carried out geophysical and geochemical investigations. Geoelectric profiles document two karstified shelf carbonate ridges lying at 10–40 m depth below calcareous lacustrine silts (and deeper more conductive sediments, likely soils/tephra) filling the plain. The smaller sags lie just above the ridges, implying a karstic origin, whereas the main sag (also resting above a carbonate ridge) shows no roots in excess of 10–20 m depth, in contrast to the "crater" interpretation. High-resolution magnetic surveys reveal negative/positive anomaly stripes in correspondence with the buried ridges/ valleys, respectively. The smaller sags, as well as the main crater are located in the domain of negative residuals. The positive long-wavelength magnetic signature is likely due to the strongly susceptive soils/tephra filling the buried valleys. Magnetic modeling shows that the field observed over the crater is incompatible with the field generated by a buried meteorite with realistic characteristics. The smaller sags are characterized by small magnetic anomaly couplets, perfectly reproducible considering the susceptibility contrast between the fill-in soil and the surrounding silts. Our data show that the Sirente crater and the minor depressions are simply the results of human activity and karstic processes, respectively.

Description: Published

Description: B03103

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.2. Laboratorio di paleomagnetismo

Description: JCR Journal

Description: reserved

Description: In the new world military scenario, potential terrorist action against port structures is of increasing concern. By this way one of the most dangerous situations is represented by individual divers’ attacks which have to be considered as critical as an intrusion conduced by military divers of an enemy nation army. In fact, divers can approach protected littoral areas by exploiting regions inaccessible to acoustic-based systems, such as acoustic shadow zones caused by natural or man made actions (i.e. irregular seabed morphology, obstacles, high reverberation regions, etc…). The magnetic detection method offers a potentially interesting solution to this problem in such regions by integrating acoustic based intruder detection systems. This paper shows the result obtained during the operative test of a port protection underwater system based on a magnetometers’ new self-informed network. The experiment takes place in a geomagnetic space characterized by medium-high environmental noise with a relevant human origin magnetic noise component. The system has two different input signals: the magnetic background field (natural + artificial noise) and a signal composed by the magnetic background field and the magnetic field due to the target (informative signal). The system uses the first signal as filter for the second one to detect the target magnetic signal. The effectiveness of this procedure is related to the position of the magnetic field observation points (reference devices and sentinel devices). The sentinel devices must obtain correlation in the noise observations and de-correlation in the target signal observations. The system, during four tries of intrusion, has correctly detected all magnetic signals generated by divers. The processing of magnetic signals has been enhanced by implementing an amplitude threshold to cut the passive energy components, which are those components that don’t contain useful information about diver passages. The use of this Passive Energy Cutter (PEC) increases the reliability of the system in terms of detection probability versus false alarm probability, as evidenced by the comparison of the ROC curves for the system with and without the PEC use.

Description: Published

Description: 538-545

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: N/A or not JCR

Description: reserved

Description: This paper deals with the problem of the electromagnetic linear inverse scattering from magnetic anomalies buried in a lossy half space, for a scalar and two dimensional case. First, the formulation of the exact model of the electromagnetic scattering is given. Then, the linear inverse problem is solved by resorting to the well assessed Singular Value Decomposition tool. The reliability of the solution procedure is tested with synthetic data achieved by a FDTD code.

Description: 147 - 158

Description: JCR Journal

Description: open

Description: Nell'ambito della ricerca "Le vie romane del Mediterraneo" è stato eseguito uno studio sulle antiche vie consolari di Roma, la via Appia antica e la via Severiana mediante l'esecuzione di campagne di misure geofisiche, finalizzate all'individuazione di tratti poco noti della viabilità antica e di resti archeologici presenti lungo tali percorsi e non visibili in superficie. I metodi geofisici impiegati nella ricerca sono stati la magnetometria, il georadar, la tomografia elettrica e la microgravimetria. Tali metodologie sono state utilizzate singolarmente o integrate tra loro secondo il tipo di struttura da individuare e relativamente al contesto ambientale.

Description: Published

Description: 29-49

Description: 3.8. Geofisica per l'ambiente

Description: reserved

Description: Tectonomagnetic field observations from absolute magnetic field levels have been collected in Central Italy since 1989 by means of a network of four absolute magnetometer stations, including the geomagnetic observatory of L’Aquila (42 23 N, 13 19 E) used as reference for differentiation; also electromagnetic variations from VLF signals have been recorded in the last years by means of VLF search coil wide-band antennas. Many reports proved the occurrence of electromagnetic effects clearly related to tectonic events (seismic and volcanic activity) in active areas of our planet. In this paper we show the variation of some electromagnetic parameters which could be related to local and regional seismic activity for the most recent years 2002 and 2003. We also report the seismic activity recorded in this area by the Italian seismic national network. Some tentative analysis (in the wavelets and statistical approach) on the historical and recent dataset allow a better characterization of electromagnetic properties of the study area, at different temporal and spatial scales.

Description: Published

Description: 925-930

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: N/A or not JCR

Description: open

Description: This paper shows the result obtained during the operative test of an anti-intrusion undersea magnetic system based on a magnetometers’ new self-informed network. The experiment takes place in a geomagnetic space characterized by medium-high environmental noise with a relevant human origin magnetic noise component. The system has two different input signals: the magnetic background field (natural + artificial) and a signal composed by the magnetic background field and the signal due to the target magnetic field. The system uses the first signal as filter for the second one to detect the target magnetic signal. The effectiveness of the procedure is related to the position of the magnetic field observation points (reference devices and sentinel devices). The sentinel devices must obtain correlation in the noise observations and de-correlations in the target signal observations. The system, during four tries of intrusion, has correctly detected all magnetic signals generated by divers.

Description: Published

Description: 100-1007

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: reserved

Description: An array of vector magnetometers was temporarily installed in the Western sector of the Anti Atlas chain, Morocco in the frame of the Geomagnetic Depth Sounding (GDS) technique. As a fruitful collaboration between Italy and Morocco, the joint project “Terremagnet”, funded by the Italian Ministry of the Foreign Affair, was aimed to local observations of the earth’s magnetic field in order to define electric conductivity horizontal and vertical contrasts in a tectonic active region. The analysis in time and frequency-domain for tests on the induced EM field dimension, computations of single site and coupled site Transfer Functions (TFs) and induction vectors configuration are shown. Recorded data are compared to Averroes geomagnetic observatory (Morocco) (IAGA code: AVE, lat. 33° 17’ 53” N, long. 7° 24’ 48” W, altitude: 230 m a.s.l.). The preliminary results from Morocco are really encouraging and pointed out good data samplings that will allow shedding up light on the tectonic setting of this peculiar region of the Anti-Atlas.

Description: Not submitted

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: 3.4. Geomagnetismo

Description: N/A or not JCR

Description: open

Description: From 2000 to 2005 two exploring geophysical missions were undertaken in the Tyrrhenian deep seafloor at depths between around -2000 and -3000 m in the framework of the European-funded GEOSTAR Projects. The considered missions in this work are GEOSTAR-2 and ORIONGEOSTAR-3 with the main scientific objective of investigating the deep-sea by means of an automatic multiparameter benthic observatory station working continuously from around 5 to 12 months each time. During the two GEOSTAR deep seafloor missions, scalar and vector magnetometers acquired useful magnetic data both to improve global and regional geomagnetic reference models and to infer specific geoelectric information about the two sites of magnetic measurements by means of a forward modelling.

Description: In press

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: open

Description: We discuss the tectonic implications of a new residual magnetic map of the Apennine belt/Adriatic-Apulian foreland obtained by integrating ground and offshore data sets [Chiappini et al., 2000a]. Negative anomalies are documented over the Adriatic-Apulian foreland areas, whereas the external Apennine belt is characterized by a ubiquitous lowamplitude (〈30 nT), long-wavelength positive anomaly. In the central northern Apennines, three 100 km wide more intense (100–200 nT) round-shaped anomalies are superimposed to the long-wavelength feature. Finally, in the Tyrrhenian Sea and margins, high-intensity, short-wavelength positive-negative couplets coincide with magmatic outcrops or bodies at shallow depth. The low-amplitude anomaly pattern over Italy suggests that the magnetic basement beneath the Triassic evaporites is ubiquitously incorporated in the external belt compressive fronts, implying a thick-skinned tectonic style for the external Apennines. The new residual magnetic map resolves the inconsistency between previous aeromagnetic data [AGIP SpA. Italia, 1981], which suggested a lack of basement involvement in the Apennine belt, and recent seismic data, which imaged deep reflectors penetrating the basement. Two magnetic models along NE-SW transects in the northern and southern Apennines suggest consistent structural styles. In the northern Apennines, positive anomalies roughly coincide with the external compressive fronts, although there are local second-order differences between the belt front and the edges of the anomaly. Here the magnetic data show that the basement rises southwestward along the thrust fronts from 6–7 km depth in the Adriatic foreland to 2–3 km depth in the axial belt, where some exploration wells have penetrated basement. Within the belt front, basement exhumation is inferred to occur along high-angle, low-displacement thrust faults inverting preexisting normal faults. In the southern Apennines, a remarkable positive magnetic anomaly is parallel with and tens of kilometers southwest of the belt front. Seismic data and oil wells show that the basement surface cannot be shallower in the belt than in the foreland. Therefore the observed magnetic anomaly is produced by strongly magnetic basement beneath the belt, likely an internal crustal wedge tectonically interposed between the Apulian carbonate sequences and basement.

Description: Published

Description: 2290

Description: JCR Journal

Description: reserved

Description: Magnetic observations over the area of the Transantarctic Mountains (TAM) and the Ross Sea have been compiled into a digital database that furnishes a new regional scale view of the magnetic anomaly crustal field in this key sector of the Antarctic continent. This compilation is a component of the ongoing IAGA/SCAR Antarctic Digital Magnetic Anomaly Project (ADMAP). The aeromagnetic surveys total 115000 line km, and are distributed across the Victoria Land sector of the TAM, the Ross Sea, and Marie Byrd Land. The magnetic campaigns were performed within the framework of the national and international Italian–German–US Antarctic research programs and conducted with differing specifications during nine field seasons from 1971 until 1997. Generally flight line spacing was less than 5 km while survey altitude varied from about 610 to 4000 m above sea level for barometric surveys and was equal to 305 m above topography for the single draped survey. Reprocessing included digitizing the old contour data, improved levelling by means of microlevelling in the frequency domain, and re-reduction to a common reference field based on the DGRF90 model. A multi-frequency grid procedure was then applied to obtain a coherent and merged total intensity magnetic anomaly map. The shaded relief map covers an area of approximately 380000 km2. This new compilation provides a regional image of the location and spatial extent of the Cenozoic alkaline magmatism related to the TAM–Ross Sea rift, Jurassic tholeiites, and crustal segments of the Early Palaeozoic magmatic arc. A linear, approximately 100-km wide and 600-km long Jurassic rift-like structure is newly identified. Magnetic fabric in the Ross Sea rift often matches seismically imaged Cenozoic fault arrays. Major buried onshore pre-rift fault zones, likely inherited from the Ross Orogen, are also delineated. These faults may have been reactivated as strike-slip belts that segmented the TAM into various crustal blocks.

Description: Published

Description: 121-137

Description: JCR Journal

Description: reserved

Description: El Hierro is the youngest of the Canary Islands, a volcanic archipelago in the central Atlantic, near the African coast. The subaerial part of the island shows the characteristic shape of three convergent ridges that has been interpreted as a triple-arm rift system. At least four giant landslides formed wide, horseshoe embayments that separate these ridges. Recent studies based on high-resolution bathymetry, however, showed that the submarine rift structure is much more complex. We analysed an aeromagnetic anomaly data set acquired in 1993 by the Spanish National Geographic Institute in order to obtain a structural model of the island from a magnetic point of view. A digital elevation model of the volcanic edifice was divided into a mesh of prismatic cells, each of them with a top corresponding to the topographic height (or bathymetric depth in the marine area) and a bottom at a constant depth of 4000 m below sea level. A three-dimensional (3-D) inversion algorithm and forward modelling along representative profiles provided us with a magnetization distribution containing valuable information about the inner structure of the island. The magnetic model cast new light on the rift structure of El Hierro. In particular, high magnetization values have been mainly interpreted as intrusive complexes on which rift zones are rooted. Their location confirms the hypothesis of a complex rift structure in the marine area. The inverse magnetization that characterizes the NE submarine rift area implies that this part of the volcanic edifice formed during the Matuyama and, therefore, predates the NW submarine rift zone, which is normally magnetized. The N–S rift zone extending southwards from the island seems to be shifted to the west with respect to the bathymetric high in this area. This result suggests that the original rift zone was located in the area where the highest magnetizations presently occur so that the present morphology may reflect the westward collapse of the original ridge. In addition, very low magnetizations characterize the areas affected by giant landslides, indicating that magnetic anomalies can provide important constraints on the distribution of these catastrophic events.

Description: Published

Description: 339-350

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: reserved

Description: Monitoring the Earth's magnetic field is carried out by geomagnetic observatories all over the world. In Italy, the first observatory was founded in 1880, when Pietro Tacchini, the director of the Central Meteorological Institute (Ufficio Centrale di Meteorologia), launched an initiative to study the distribution of the Earth's magnetic field over the Italian territory.

Description: Published

Description: 733

Description: 1.6. Osservazioni di geomagnetismo

Description: 3.4. Geomagnetismo

Description: 5.3. Banche dati di geomagnetismo, aeronomia, clima e ambiente

Description: reserved

Description: 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).

Description: Submitted

Description: 1.6. Osservazioni di geomagnetismo

Description: 3.4. Geomagnetismo

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: JCR Journal

Description: open

Description: The use of the integral moments for interpreting magnetic data is based on a very elegant property of potential fields, but in the past it has not been completely exploited due to problems concerning real data. We describe a new 3-D development of previous 2-D results aimed at determining the magnetization direction, extending the calculation to second-order moments to recover the centre of mass of the magnetization distribution. The method is enhanced to reduce the effects of the regional field that often alters the first-order solutions. Moreover, we introduce an iterative correction to properly assess the errors coming from finite-size surveys or interaction with neighbouring anomalies, which are the most important causes of the failing of the method for real data. We test the method on some synthetic examples, and finally, we show the results obtained by analysing the aeromagnetic anomaly of the Monte Vulture volcano in Southern Italy.

Description: Published

Description: 815-824

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: JCR Journal

Description: reserved

Description: In the following, we report the advances made in the development of a magnetic component for peripheral monitoring of port environments for anti-intruder systems. The project was initiated by the Office of Research and Development, COMFORDRAG, Italian Navy, in 2004, with the aim of improving the detection performance of current acoustic-based anti-intruder systems, in the vicinity of quays or the seabed or in acoustic-shadow zones behind natural or artificial objects. In the five-year period from 2004 to 2008, the system has been subjected to detection-performance tests in experiments involving divers equipped with air tanks and rebreather kits in real port environments and, at the same time, the associated signal processing has been subjected to development, to enhance detection performance. In tests involving simulated diver attacks against a vessel moored alongside a quay in the port of La Spezia, the system has been proved particularly effective by detecting 9 divers out of 9. The processing of the magnetic signal has been enhanced by implementing an amplitude threshold, as a means of filtering the passive energy components, termed Passive Energy Cutting (PEC), that is, the elimination of components that comprise no useful information regarding diver transits. The use of PEC boosts the reliability of the system in terms of detection versus false alarm rate, as evidenced by the comparison of the ROC curves for the system with and without PEC.

Description: Naval Team Denmark, Denmark NATO Undersea Research Centre (NURC), Italy RESON A/S, Denmark Technical University of Denmark (DTU), Denmark Gdansk University of Technology, Poland UltraTech Holding, Denmark Terma A/S, Denmark OES Japan Chapter, Japan Office of Naval Research Global Homeland Security

Description: Published

Description: Technical University of Denmark, August 25-28, Copenhagen, Denmark, 2008

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: 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 available observatory 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.

Description: Published

Description: 1192

Description: JCR Journal

Description: reserved

Description: Potential field data hold a leading role in the geologic-structural application. Their use becomes even more important if applied to extremely inaccessible zones as oceanic basins or no-antropized area. By an areo-naval survey it is possible to cover large areas, in a short time, to define their deep crustal features that are otherwise not accessible by other direct methods. The analysis of the magnetic field data is particularly effective 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 about the 41st parallel zone starting from potential field data. The name 41st parallel indicates a geographic zone aligned along N41st of latitude. This area is longitudinally defined between the Continental Campanian Margin (Naplean Gulf, Ischia and Procida island) and the northwestern portion of the Sardinia Island. From a geological point of view, the 41st parallel represents a complicate area. Several geological structures are located along this zone: submerged volcanic bodies such as the Etruschi, Vercelli and Cassinis seamounts, emerged edifices connected to the Pliocenic-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 and is still object of discussion in literature. The structural setting of 41st parallel zone is highlighted only by magnetic field data. By the observation of the magnetic anomalous field it is possible to see an alignment 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 suggest these features. To this aim, I use the magnetic data to analyse in quantitative way, the 41st parallel zone. The magnetic data used for the development of the 3D magnetic model derived by the 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 aeromagnetic surveys 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 data the 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 structural features 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 using two 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 third chapter 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 from the regional heat-flow data (Della Vedova et al., 2001) of the Central Tyrrhenian area the Curie Isotherm surface is modeled defining the maximum 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 obtain the 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 development of the magnetic generating sources suggesting the geometric relationship between the different sources. These information are important for evaluating the crustal setting of the study area. Finally, in the last chapter 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 models of these two regions I provide a chronological reconstruction of the geodynamic evolution of the Central Tyrrhenian Sea.

Description: Università di Bologna

Description: Unpublished

Description: 3.3. Geodinamica e struttura dell'interno della Terra

Description: 3.4. Geomagnetismo

Description: 3.5. Geologia e storia dei sistemi vulcanici

Description: open

Description: Antarctica is the most poorly understood region of our planet. It, however, maintains an important geologic record of the Gondwana and Rodinia evolution and therefore is a center of extensive scientific inquiry. Magnetic data provide a critical window for geological studies due to the nearly ubiquitous snow and ice cover of this forbidding region. Consequently, numerous magnetic surveys have been carried out for site-specific geologic objectives since the International Geophysical Year 1957/1958. Plans for an international project to process and combine these disparate data sets into a single magnetic anomaly map were formulated at the 1993 meeting of the International Association of Geomagnetism and Aeronomy (IAGA) in Buenos Aires, Argentina. Both IAGA and the Scientific Committee on Antarctic Research (SCAR) passed resolutions of encouragement (Johnson et al., 1996; Chiappini et al., 1999). At a 1995 workshop at the British Antarctic Survey in Cambridge, UK, it became clear that these individual magnetic surveys could indeed be combined into a regional synthesis to further enhance their utility for geological studies (Johnson et al., 1996, 1997; Chiappini et al., 1998, 1999). Accordingly, the Antarctic Digital Magnetic Anomaly Project (ADMAP) was launched at this first workshop (ADMAP I) to compile and integrate into a digital database existing near-surface and satellite magnetic anomaly data of Antarctica and the surrounding oceans south of 60jS. An international working group of 32 scientists from eight countries that operate magnetic programs in the Antarctic was established. The working group adopted protocols for making existing and future magnetic data sets available to this international effort. In particular, existing Antarctic magnetic data holdings will be deposited in the world data centers by the end of this first phase of the project in 2002.

Description: Published

Description: 1-2

Description: 3.2. Tettonica attiva

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: reserved

Description: The science of environment is per se multi- and inter-disciplinary. It is not possible to separate the role of the physical, chemical, biological, and anthropic factors, respectively. Research must therefore rely on suitable natural laboratories, where all different effects can be simultaneously monitored and investigated. Stromboli is a volcanic island slightly North of Sicily, within a tectonic setting characterised by a Benioff zone, curved like a Greek theatre, opened towards the Tyrrhenian Sea, with deep earthquakes. Moreover, it is a unique volcano in the world in that since at least ~ 3000 years ago, it has exploded very regularly, about every 15^20 min. Hence, it is possible to monitor statistically phenomena occurring prior, during, and after every explosion. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) has recently established a permanent Laboratory and an extensive interdisciplinary programme is being planned. A few main classes of items are to be considered including: (1) matter exchange (solid, liquid, gas, chemistry); (2) thermal and/or radiative coupling; (3) electromagnetic coupling; (4) deformation; (5) biospheric implications; and (6) anthropic relations since either the times of the Neolithic Revolution. Such an entire multidisciplinary perspective is discussed, being much beyond a mere volcanological concern. We present here the great heuristic potential of such a unique facility, much like a natural laboratory devoted to the investigation of the environment and climate.

Description: Published

Description: 429-442

Description: JCR Journal

Description: reserved

Description: 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 Magnetic Anomaly Map).

Description: Published

Description: 101-109

Description: 1.6. Osservazioni di geomagnetismo

Description: 3.4. Geomagnetismo

Description: 5.3. Banche dati di geomagnetismo, aeronomia, clima e ambiente

Description: JCR Journal

Description: reserved

Description: A high-resolution aeromagnetic survey (altitude 125 m asl, spacing 500 m , area 800 km2) was carried out in 1994 offshore of Cape Roberts by the GITARA (German ITalian Aeromagnetic Research in Antarctica) Group. The availability from drilling of whole-core physical properties logs for magnetic susceptibility, P-wave velocity and density/porosity data allows new insights to be inferred from reprocessed and reviewed HRAM aeromagnetic data. Aeromagnetic data have been reprocessed to image with greater detail the structural framework along the western flank of the Victoria Land Basin. New processing includes 2D Werner and 3D Euler deconvolution, the production of maps of the maximum horizontal gradient of pseudo-gravity, and 2D, 3D modelling. Magnetic trends and anomalies are discussed in conjunction with now available drilling results from the CRP, existing bathymetric data and recently published interpretations of a multichannel seismic reflection survey.

Description: Published

Description: Santa Barbara, CA, USA

Description: 3.4. Geomagnetismo

Description: open

Description: We show a set of forward model equations in the Fourier domain for calculating the 3D gravity and magnetic anomalies of a given 3D distribution of density or magnetization. One property of the potential-field equations is that they are given by convolution products, providing a very simple analytic expression in the Fourier domain. Under this assumption, the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space, and potential-field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions. A very fine spatial discretization can be obtained by using a large number of points within a unique 3D grid, where both the source distributions and field data are defined. The main advantage of this formulation is that it dramatically reduces execution times, providing a very fast forward model tool useful for modeling anomalies at different altitudes. We use this method to evaluate an average magnetization of 8 A/m for the Palinuro Seamount in the Tyrrhenian Sea (Southern Italy), thus performing a joint interpretation of morphological and newly acquired magnetic data.

Description: In press

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: JCR Journal

Description: open

Description: La frontiera della ricerca della geofisica moderna si fonda in maniera rilevante su due direttrici al crocevia tra scienza e tecnologia: il progresso tecnologico nella strumentazione per le misure e l'affinamento della capacità di gestione ed elaborazione delle informazioni raccolte. Come in ogni altra scienza sperimentale, i dati e la capacità di saperli analizzare rappresentano pilastri fondamentali nella ricerca geofisica. Allo stato attuale l'Europa è messa a confronto con l'impressionante sviluppo che sta avvenendo in Paesi quali Giappone e Usa. Un esempio significativo è rappresentato dalla campagna di misure sull'isola di Tenerife, alle Canarie, a opera dell'Istituto Nazionale di Geofisica e Vulcanologia presieduto da Enzo Boschi e il Consejo Superior de Investigaciones Cientificas spagnolo. Il grande vulcano Teide, che domina l'isola e che è giudicato dagli esperti "ad alto rischio", è stato investigato con una tecnica di rilevamento innovativa, chiamata aeromagnetismo. Per svelare i segreti dell'edificio vulcanico sottomarino, fin dentro la crosta terrestre, gli scienziati hanno operato dal cielo, a bordo di un elicottero attrezzato con apparati di alta tecnologia sospesi in una sorta di missile che al suo interno ospita i sensori che captano i campi magnetici delle rocce vulcaniche. I rilievi aeromagnetici effettuati consentiranno di identificare le strutture sepolte, in modo tale da ricostruire formazioni come condotti lavici, crateri e faglie. Un contributo (non solo a beneficio della geofisica ma anche della Protezione Civile spagnola) che è stato realizzato con una tecnologia avanzata, fiore all'occhiello dell'Italia e dell'Istituto Nazionale di Geofisica e Vulcanologia. Si tratta inoltre di un esempio estremamente interessante, di cooperazione tra istituzioni italiane ed europee che risulta affiancato da un protocollo ministeriale tra Italia, Spagna e Portogallo realizzato nel 2005 con il sostegno della Fondazione Cotec. La fisica dei terremoti e dei fenomeni vulcanici non soltanto non rispetta le frontiere nazionali coinvolgendo spesso Paesi limitrofi ma (si pensi ai grandi mercati primari e secondari di assicurazione) ne coinvolge in maniera tanto pervasiva le economie da richiedere risposte di impegno e coordinamento di statura europea.

Description: Published

Description: 7

Description: 1.8. Osservazioni di geofisica ambientale

Description: 3.4. Geomagnetismo

Description: 3.8. Geofisica per l'ambiente

Description: N/A or not JCR

Description: open

Description: Non-acoustic detection systems can be used in combination with Sonar systems to determine the presence of an underwater threat, such as terrorist divers. The goal of the CAIMAN (Coastal Anti Intruders MAgnetometers Network) joint experiment (Italian Navy, NATO Undersea Research Centre and INGV Marine Geophysics) is the application of High Definition Geophysics Magnetic techniques in a port protection scenario, where conventional measurements of very low magnetic sources, like intruder swimmers, are strongly disturbed by ambient, natural and artificial, background noise and other time-variant magnetic anomalies. Two tri-axial fluxgate magnetometers were deployed on the sea bottom and connected to a shore side measurement station. A team of navy divers, wearing both COTS and EOD equipment, performed some coastal approach runs on each magnetometer alternatively. Magnetic signature data were logged and post processed using MATLAB®. Results demonstrated the effectiveness of high definition time reduction techniques using a self-referred integrated array design.

Description: Published

Description: Naples, Italy, June 5-7, 2007

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: In May 2007, following a request by Italian Navy (ITN), NURC agreed to provide the technology, developed during the port protection studies and 2006 MCM ops. in Baltic sea for Estonian Navy, to survey part of the Capo Teulada firing range (Sardinia Island, Italy), used by NATO Armed Forces. The goal of the service, fully funded by ITN, was to survey part of the firing range with acoustic, magnetic and optical instruments in order to detect and classify the ordnance laying on the seafloor. The team operated from CRV Leonardo to produce a detailed acoustic and magnetic map of the area. The positions of the targets of interest have been provided to Italian Navy for further identification and disposal. The activities have demonstrated that the NURC Autonomous Underwater Vehicles (AUVs) Remus type equipped with high frequency side scan sonar can detect and classify targets of the dimensions of unexploded ordnance laying proud on the sea floor. A multiple sonar images technique has also been used to improve the classification performances. However, in some areas, targets that were completely buried or concealed in Posidonia fields wouldn’t have been detectable with AUV sonar. To overcome this limitation, INGV supported the NURC team by using a new high definition magnetometer technique to detect and classify buried metal targets. A proton Overhauser sensor was towed from Leonardo vessel and a magnetometer reference station was set ashore in an appropriate site. A subset of interesting contacts (acoustic and magnetic) have been identified optically by means of the video camera installed on the ROV (Pluto Plus type by Gaymarine) operated from Leonardo. The positioning accuracy achieved was fully compatible with the reacquisition by ROV and then by divers or mine hunters for future disposal ops. The survey has also produced an accurate map of the Posidonia fields and a detailed bathymetry of the area. More than 300 contacts have been acquired and more than 200 were classified in less than 15 days. The success of Teulada operation has convinced ITN to ask NURC for a common development programme with the aim to validate at sea a fully integrated multi-sensor approach (sonar, magnetic and optical) in MCM short term ops. using USV/AUV platforms.

Description: Published

Description: Scottish Exhibition and Conference Centre (SECC), Glasgow, 10-12 June 2008

Description: 1.6. Osservazioni di geomagnetismo

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: 3.4. Geomagnetismo

Description: open

Description: In this paper we show and discuss the results of gravity and magnetic surveys of Panarea Island and its archipelago. The most recent volcanic manifestation occurred in November 2002 with a shallow submarine gas eruption between the islets of Dattilo, Panarelli, Lisca Bianca, Bottaro and Lisca Nera. Currently, the activity of Panarea is monitored through a multidisciplinary study under the umbrella of the Italian Department of Civil Protection with the goal of defining the hazard of this area. With this aim, in May 2006 the first gravity and magnetic surveys of Panarea Island and its archipelago were performed. The offshore magnetic data were obtained using a marine magnetometer, a Geometrics G880, from the Istituto Idrografico dell Marina (IIM). Onshore and offshore magnetic data were integrated into an unique dataset for complete magnetic coverage of the study area. By using two micro-gravimeters (LaCoste & Romberg), gravity data were collected along tracks every 250 meters. The gravity dataset was processed using the standard method. A Bouguer reduction was applied to the free-air gravity dataset using a detailed digital elevation model of the island and the neighbouring sea after evaluation of the optimal Bouguer density to reduce the topographic effect. The result is a Bouguer anomaly map that shows lateral variations in density distribution and the relationships between the shallow volcanic/crustal features and tectonic lineaments. This evidence is also highlighted by the magnetic pattern, which suggests the importance of the youngest volcanic deposits with respect to the magnetic features of the island.

Description: Published

Description: 25-38

Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: open

Description: Reliability of high resolution airborne and shipborne magnetic surveys depends on accurate removal of temporal variations from the recorded total magnetic field intensity data. At mid latitudes, one or a few base stations are typically located within or near the survey area and are used to monitor and remove time dependent variations. These are usually assumed to be of external origin and uniform throughout the survey area. Here we investigate the influence on the magnetic base station correction of the time varying magnetic field variations generated by internal telluric currents flowing in anomalous regional 2D/3D conductivity structures. The study is based on the statistical analysis of a data set collected by four magnetovariational stations installed in northwestern Italy. The variometer stations were evenly placed with a spacing of about 60 km along a profile roughly parallel to the coastline. They recorded the geomagnetic field from the beginning to the end of April 2005, with a sampling rate of 0.33 Hz. Cross-correlation and coherence analysis applied to a subset of 125 five hours long magnetic events indicates that, for periods longer than 400 s, there is an high correlation between the horizontal magnetic field components at the different stations. This indicates spatial uniformity of the source field and of the induced currents in the 1D Earth. Additionally, the pattern of the induction arrows, estimated from single site transfer functions, reveals a clear electromagnetic signature of the Sestri-Voltaggio line, interpreted as a major regional tectonic boundary. Induced telluric currents flowing through this 2D/3D electrical conductivity discontinuity affect mainly the vertical magnetic component at the closer locations. By comparing this component at near (32 km) and far (70 km) stations, we have found that the mean value of the power spectra ratio, due to the electromagnetic induced field, is about 1.8 in the frequency band ranging from 2.5×10−3 to 5.5×10−5 Hz. This energy, folded in the spatial domain of an hypothetical survey in this region produces unwanted noise in the dataset. Considering a fifth of nyquist frequency the optimal tie-line spacing to assure complete noise removal would be 1 km and 15 km for a rover speed of 6 knots (marine magnetic survey) and 100 knots (aeromagnetic survey) respectively. Similar power spectra analysis can be applied elsewhere to optimise tie-line spacing for levelling and filtering parameters utlilised for microlevelling.

Description: Published

Description: 397-406

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: open

Description: The present essay is the result of a cooperative work between geophysicists and archaeologists in which the authors carried out an integrated geophysical prospecting in an archaeological site near Rome. This paper describes the methodology and the results of a geophysical survey carried out on Villa ai Cavallacci, an ancient roman building in Albano Laziale (Rome) discovered in the late seventies. It is often possible to obtain very important results planning a fast geophysical survey opportunely; within this framework (due to the fact that an archaeological excavation was planned in a short time), an integrated geophysical techniques survey (GPR, magnetic, and geoelectric tomography) has been carried out on the areas indicated by the archaeologists. Even if the described geophysical survey should be considered only a first step analysis, the data pointed out some very interesting features confirmed by the excavation.

Description: Published

Description: 291-299

Description: 1.8. Osservazioni di geofisica ambientale

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: open

Description: The study of the Calabrian Arc in the Ionian Sea is key to understanding of the geological processes in the Mediterranean Sea. We present the technical details and results of cruise CALAMARE08 with N/O Urania during spring 2008. We acquired a large set of geological and geophysical data, among them Multichannels Seismic and SBP, magnetometry, gravimetry, swath bathymetry and coring of sea bottom.

Description: 1. CNR, Istituto Di Scienze Marine, Bologna, Italy 2. Dipartimento Sc.della Terra, Universita- di Parma 3. Universita’ di Bologna 4. Universita’ di Roma-3 5. Universite’ Brest 6. Istituto Nazionale di Geofisica e Vulcanologia, Roma-2, Roma, Italy 7. Istituto Idrografico della Marina, Genova

Description: Published

Description: 3.2. Tettonica attiva

Description: open

Description: The estimation of the direction of the total magnetization vector of a magnetic source is the first step of a reliable modelling of a magnetic anomaly when remanent magnetization is not negligible. We present a new method to obtain the magnetization direction of a crustal body, based on an iterative equivalent layer inversion of a magnetic anomaly. The main advantage of the proposed approach is that no a priori information about the source is needed. The method is suitable for the interpretation of isolated magnetic sources for which magnetization is expected to be uniform in direction, but not necessarily in intensity.We have verified the success of the technique with synthetic data and with the magnetic anomaly of El Hierro volcanic island.

Description: Published

Description: 163–169

Description: reserved

Description: The technological and the scientific objectives of the MEM (Magnetic and Electric fields Monitoring) project concerning to the study of the electromagnetic signals linked with the Earth’s crustal activity are reported. The MEM project has been activated in Central Italy to create a network of observatories so as to monitoring the electromagnetic signals, both natural and artificial, in the frequency band [0.001 Hz-100 kHz]. Some examples of the developed instrumentation and the know-how transfer to the industry are reported. We also report some results obtained in the first MEM station installed in the area of the INGV (Italian Istituto Nazionale di Geofisica e Vulcanologia) Observatory of L’Aquila. Using the single station magnetotelluric approach we have obtained some valuables information about the underground resistivity structure in the area of the measurement station. Concerning to the study of the magnetic signals linked with the tectonic activity we have reported an example of the long term behaviour of the magnetic induction vectors characteristics in the lower frequency band [0.001-0.5] Hz, showing their normal behaviour when no large crustal changes due to geodynamical processes are present.

Description: INGV MEM Project

Description: Published

Description: 507-511

Description: 1.6. Osservazioni di geomagnetismo

Description: JCR Journal

Description: open

Description: It has been reported that earthquakes and volcanic eruptions produce significant variations in the geomagnetic field. To investigate possible tectonomagnetic effects related to seismic activity, the Istituto Nazionale di Geofisica installed a seismomagnetic network in central Italy; the area was selected after a magnetic noise survey. Geomagnetic field intensity data are simultaneously recorded at four magnetometer stations and at L’Aquila Geomagnetic Observatory, which is located in the same area. The data are differentiated in order to detect local magnetic field anomalies. The present study reports geomagnetic field observations in central Italy from July 1989 to March 1995 and also discusses the detectability of a tectonomagnetic effect in this area. A variation of about 5 nT over a two-month period January–February 1990.has been observed in the geomagnetic field. No other anomaly has been observed, although moderate seismicity occurred in central Italy during the study period.

Description: Published

Description: 145-152

Description: JCR Journal

Description: open

Description: Salina Island (Italy) is located in the central sector of the Aeolian Islands and represents the northernmost volcanic structure of an elongated ridge emplaced on a regional shear zone characterized by NNW-SSE strike-slip faults and by second order N-S and NE-SW faults. High-resolution, low-altitude aeromagnetic data collected in 2003 and 2005 allow us to study the subsurface structure of Salina Island. The magnetic data show a pattern with a wide range of wavelengths and intensities. Magnetic modeling constrained by volcanological data allow us to reconstruct the inner structure of the Salina volcanoes and surrounding marine regions. Long wavelength negative anomalies overlap E-W elongated sedimentary basin related to the Early Pliocene-Pleistocene opening of the Southern Tyrrhenian Sea back-arc basin. The shorter wavelength positive magnetic anomalies are related to the Late Pleistocene-Holocene volcanic (conduits, dikes) and tectonic (faults) structures. The magnetic and volcanological data indicate that the early (168- about 100 ka), basaltic to basaltic andesitic Salina volcanism developed along N-S and NE-SW tectonic structure, whereas the more recent basaltic andesitic to rhyolitic products (about 100-13ka) were emitted by vents related to the main NW-SE fault tectonic structures. The tectonic structures also control the location of the seamounts around the island and the geometry of the volcano-tectonic collapses. The Salina volcanism emplaced on a NNW-SSE regional discontinuity that represents a tear fault of the present-day roll-backing slab in the Southern Tyrrhenian Sea.

Description: Published

Description: 1.6. Osservazioni di geomagnetismo

Description: JCR Journal

Description: open

Description: It is well established that earthquakes and volcanic eruption can produce small variations in the local geomagnetic field. The Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) tectonomagnetic network was installed in Central Italy since 1989 to investigate possible effects on the local geomagnetic field related to earthquakes occurrences. At the present time, total geomagnetic field intensity data are collected in four stations using proton precession magnetometers. We report the complete dataset for the period of years 2004-2005. The data of each station are differentiated respect to the data of the other stations in order to detect local field anomalies removing the contributions from the other sources, external and internal to the Earth. Unfortunately, no correlation between geomagnetic anomalies and the local seismic activity, recorded in Central Italy by the INGV Italian Seismic National Network, was found in this period. Some deceptive structures present in the differentiated data are pointed out.

Description: INGV

Description: Published

Description: 773-777

Description: 1.6. Osservazioni di geomagnetismo

Description: open

Description: In this paper, we present a magnetic model of the subsurface structure of Vulcano island based on highresolution aeromagnetic data. Three profiles across the most intense magnetic anomalies over the Piano and Fossa calderas were selected for the magnetic modelling, which was constrained by structural and volcanological data, previous geophysical models, paleomagnetic data, and borehole stratigraphy obtained from two deep wells. The interpretation of the magnetic sources represents a significant contribution to the understanding of the Piano and Fossa calderas’ underlying structure, providing us with evidence of the lateral discontinuity between them at depth. We propose that the positive magnetic anomalies in the Piano caldera area are caused by: (a) the remnants of an early submarine volcano; (b) an outcropping dyke swarm related to the feeding system of the Primordial Vulcano phase (beneath Mt. Saraceno); and (c) the presence of a non-outcropping dyke system intruded along a NE–SWoriented intra-caldera fault (beneath the eastern part of the Piano caldera). Offshore, to the west, the magnetic anomaly map suggests the presence of a submarine volcanic structure, not revealed by bathymetric data, which represent the eruptive centre, the presence of which has been indirectly deduced from the outcrop of eastern-dipping lavas on the western seashore. Magnetic modelling of the Fossa caldera points to the presence of a highly magnetized cone-like body inside the Fossa cone, centred beneath the oldest crater rims. We interpret this body as a pile of tephritic lavas emplaced in an early phase of activity of the Fossa cone, suggesting that the volume of mafic lavas that erupted at the beginning of the construction of the Fossa edifice was more significant than has previously been deduced. Furthermore, the presence of a magnetized body inside the Fossa cone implies that high temperatures are contained in very limited spaces, do not affect its bulk inner structure, and are restricted to fumarolic conduits and vents. In addition, structures beneath the western and northern part of the Fossa caldera are revealed to have null or low magnetization, which can be ascribed to the presence of pyroclasts and hyaloclastites in this area as well as to a large volume of hydrothermally altered materials. This suggests that the hydrothermal system, with a very limited extension at present, affected a larger area in the past, especially beneath the western part of the caldera.

Description: Published

Description: 643-659

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: reserved

Description: A network of three absolute magnetometer stations and the geomagnetic Observatory of L'Aquila (42º 23N, 13º 19E) allow to monitor possible seismo- or tectonomagnetic effects in Central Italy, using L’Aquila observatory as a reference for differentiation. A system of two VLF search coil wide-band antennas, working in two different frequency bands, at the L’Aquila Observatory, allows to monitor possible electromagnetic effects related to seismic events occurring in Central Italy. Absolute magnetic field observations and VLF signals have been collected for several years. In particular the tectono-magnetic network started its operations in 1989. In this paper we report on the time variation of above mentioned data for the most recent years 2002 and 2003, also in connection to older measurements time series; we also report on seismic activity recorded in this area by the national seismic network. In the above mentioned time interval, no strong earthquake activity was recorded, and at the same time no clear evidence for magnetic or electromagnetic signals related to seismic events was found.

Description: Unpublished

Description: open

Description: In the middle of 1989, the INGV (Italian Istituto Nazionale di Geofisica e Vulcanologia) installed in Central Italy a network of magnetic stations in order to investigate possible relationship of the local magnetic field with earthquakes occurrences. Actually the network consists of four stations, where the total magnetic field intensity data are being collected using proton precession magnetometers. Here we are report on the actual state and the future developments of the network. In the frame of the MEM (Magnetic and Electric fields Monitoring) Project, new stations will be added to the network by the end of 2007. The results of the test campaigns carried out in the sites chosen to widen the network are also discussed. Moreover, the 2006 complete data set of the network is also reported. Concerning the data analysis, a new approach is also discussed that takes into account the inductive effects on the local geomagnetic field by means of the inter-station transfer functions time variations analysis.

Description: INGV MEM Project

Description: Published

Description: 473-478

Description: 1.6. Osservazioni di geomagnetismo

Description: JCR Journal

Description: open

Description: The interpretation of the potential ¯eld data is an useful tool that allows for both investigating the subsurface structures and providing a quantitative evalu- ation of the geophysical process preceding and accompanying period of volcanic unrest. Potential ¯eld inversion problem are required to combine forward mod- els with appropriate optimization algorithms and automatically ¯nd the best set of parameters that well matches the available observations. Indeed, investi- gations on the mathematical equations to be inverted, have revealed that these models are ill-posed and highly non-linear. Numerical methods for modeling potential ¯eld observations are proposed and applied on real dataset.

Description: Published

Description: open

Description: We discuss here the forward magnetic modeling, along a southern Apennines transect, of the new magnetic map of Italy (CHIAPPINI et alii, 2000a). This map has been realized through an integrated digital magnetic anomaly database built for the Italian territory and the surrounding sea. For the first time, all the magnetic observations made onshore and offshore the Italian peninsula have been compiled into a new digital database, that gives a complete regional scale view of the magnetic anomaly crustal field over the area. The new magnetic map shows a low-amplitude (~20 nT), long-wavelength positive anomaly along the external southern Apennines, and negative anomalies over both the Tyrrhenian margin of southern Italy and the Apulian foreland. South of the Vulture volcano (~41° N), the positive magnetic anomaly is elongated and exactly parallel to the external belt. Furthermore, the eastern anomaly margin is exactly parallel to the belt front, and located few tens of kilometers southwest of it. The negative pattern of the Tyrrhenian Sea and margins is likely due to the high thermal flow, which significantly reduces the thickness of the susceptive crustal layer. A magnetic modeling was performed along a selected southern Apennines transect (located ca. 50 km south of the CROP04 profile), where the shallow crustal setting (down to 5-6 km depth) is well-known by seismic and drill-hole data. Seismic data and oil wells suggest that the top of the magnetic basement cannot be shallower in the belt than in the Apulian foreland, where it was reached at ~6 km depth by the Puglia 1 well. Therefore, the positive signature of the external southern Apennines requires a strongly magnetic body beneath the belt. This source must be definitely more susceptive than the basement of the Apulian foreland. Since the solution of magnetic modeling is not unique, we show here three different settings that are able to bring into coincidence the observed and modeled residuals. First, we speculate that, within the belt, the basement located beneath the Apulian carbonates (Apulian basement) is differentiated and contaminated at depth by susceptive magmas or mantle fluids. Then, we explore the possibility that a very magnetic composite internal crustal wedge is tectonically interposed between the Apulian carbonates and basement. Two possible settings of such composite wedge are modeled and discussed. The uniformity of the magnetic anomaly pattern along 250 km of the belt, the remarkable parallelism between the southern Apennine positive residuals and the superficial belt front, associated with the gravity data, the estimates of Moho depth, and the flexural behavior of the Apulian lithosphere beneath the belt, support the two latter models.

Description: Published

Description: 13-20

Description: 3.4. Geomagnetismo

Description: JCR Journal

Description: reserved

Description: The active Vulcano Island (Southern Tyrrhenian Sea) represents the southernmost portion of a NW-SE elongated volcanic ridge that includes also Lipari and Salina islands. The ridge is affected by a regional, NW-SE to N-S striking fault system. The elaboration and analysis of data from three high-resolution aeromagnetic surveys carried out between 1999 and 2004 on Vulcano and offshore allow us to recognize high intensity magnetic anomalies related to volcanic centers/conduits or shallow intrusions. Previously unreported offshore submarine vents have been also recognized. Some of them may correspond with source areas of outcropping exotic pyroclastics on Vulcano. The spatial analysis of the recognized magnetic anomalies and volcanic structures shows that they are preferably aligned along the strikes of the main regional faults that affect the volcanic ridge. Submarine volcanic conduits revealed by the aeromagnetic survey might represent potential sources for future submarine, effusive or explosive activity.

Description: Published

Description: L15305

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: reserved

Description: This study presents magnetic anomaly data from a new high-resolution, low-altitude helicopter-borne magnetic survey recently collected on and offshore Tenerife in the Canary Archipelago. The Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) in collaboration with the Museo Nacional de Ciencias Naturales of the CSIC of Spain conducted the survey in 2006. The data for Tenerife and surrounding marine areas were processed into digital total intensity magnetic anomalies for geomagnetic epoch 2006.4. Relative to previously available higher altitude magnetic survey data, the new survey mapped higher resolution anomalies with significantly improved spatial details, especially over the Las Cañadas caldera and Teide-Pico Viejo complex in the central part of the island. A good correlation is evident between known structural geology and the magnetic anomalies, where the new shorter wavelength anomalies facilitate more detailed and comprehensive geologic interpretations.

Description: Published

Description: 689-697

Description: 3.8. Geofisica per l'ambiente

Description: 3.4. Geomagnetismo

Description: 4.4. Scenari e mitigazione del rischio ambientale

Description: JCR Journal

Description: open

Description: A magnetic anomaly map and a free air anomaly map of Prydz Bay, of the adjacent slope and over the continental rise area (63°S-69.5°S, 69°E-81°E) were compiled using Russian, Australian, Japanese and other available data (more than 20 000 km in total length). Adjustment of different data sets was performed before gridding and making contour maps. Crossover differences of the magnetic data were significantly reduced by removing data segments with short-period time variations, by applying time variation corrections of Mawson Station to Australian and Japanese data, and by giving a constant bias to each trackline. Crossover differences of the gravity data were also substantially reduced by applying a constant bias to each cruise/leg. According to the compiled gravity data, in the western part of Prydz Bay the continent ocean boundary is inferred to be situated around the shelf edge at the seaward end of Prydz Channel, while it is in the continental rise in the eastern part. The gravity data also suggest the presence of sediments in the Prydz Bay basin reaching a thickness of about 8 km and overlying a "granitic" layer; the Moho beneath the basin is located at a depth of about 22 km. According to the magnetic data, highly-magnetized rocks occur at shallow depths northwest of the Prydz Bay basin and other parts of Prydz Bay.

Description: JCR Journal

Description: open

Description: The ground magnetic measurements in Albania were used for the compilation of the Total Magnetic Field (TMF) anomaly map of Albania. The magnetic data were processed and interpreted in order to study the structure of the ophiolitic belts of Albania. The ophiolites of Albania are placed at the Mirdita zone and are divided into two parallel alignments which are called the eastern and western ophiolitic belts. They are associated with strong potential field anomalies and their characteristics are considered crucial for a better understanding of the tectonic settings of Albania. The ground TMF data used in this study were acquired over various campaigns (1990-1994) and cover most of Albania's territory. The data were compiled to a map after reduction to the epoch 1990.4. The strongest magnetic anomalies in Albania appear along the known ophiolitic belts which trend NE-SW to the north and NW-SE to the south. Several processing steps were applied to the unified and gridded data in order to obtain information on the distribution of the magnetic sources. The magnetic sources were subsequently modeled using a 2.5D inversion technique. The magnetic properties of the ophiolites determined from laboratory measurements on rock samples, while their lateral extent was calculated from the processing of the magnetic data and used as constraints to the inversion procedure. The bottom of the ophiolitic belts is considered to be predominated by harzburgites. They exhibit lower magnetization than other rocks of the complex, i.e. gabbros, basalt. In fact gabbros are associated with the observed high frequency magnetic anomalies. The modeling results indicate that the thickness of the ophiolites is reduced from east to west. The eastern ophiolitic belt has a maximum thickness of approximately 12 km at its northern section (Kukesi and Lura massifs). The magnetic sources appear with relatively small thickness at the western ophiolitic belt. Boundaries of the eastern ophiolites are characterized by vertical contacts.

Description: Published

Description: JCR Journal

Description: open

Description: The aim of this work is the formulation of a 3D model of the Mt. Amiata volcanic complex (Southern Tuscany) by means of geomagnetic data. This work is shown not only as a real test to check the validity of the inversion algorithm, but also to add information about the structure of the volcanic complex. First, we outline briefly the theory of geomagnetic data inversion and we introduce the approach adopted. Then we show the 3D model of the Amiata volcano built from the inversion, and we compare it with the available geological information. The most important consideration regards the surface distribution of the magnetization that is in good agreement with rock samples from this area. Moreover, the recovered model orientation recall the extension of the lava flows, and as a last proof of validity, the source appears to be contained inside of the topographic contour level. The credibility of the inversion procedure drives the interpretation even for the deepest part of the volcano. The geomagnetic signal appears suppressed at a depth of about 2 km, but the most striking consequence is that sub-vertical structures are found even in different positions from the conduits shown in the geologic sections. The results are thus in good agreement with the information obtained from other data, but showing features that had not been identified, stressing the informative power of the geomagnetic signal when a meaningful inversion algorithm is used.

Description: Published

Description: JCR Journal

Description: open

Description: Analysis of the analytic signal of the aeromagnetic field in the Tyrrhenian region allowed the systematic location of the boundaries of magnetic shallow sources. This method was chosen because of its independence from the magnetization and inducing field direction, and the results were similar to those of the boundary analysis of the horizontal gradient of the pseudogravity transformed field. The analytic signal was computed by a stable algorithm based on the second order horizontal derivatives of the field and Laplace equation. The complexity of the investigated area is well reflected in the aeromagnetic field and an objective and systematic study, such as boundary analysis, provided a rather complete description of the main regional structures. Significant trends indicated the existence of structures, whose nature was still unknown or uncertain. These included structures located between the Vavilov and De Marchi seamounts, NW of Stromboli Island, south of Ponza Island, a buried horst immediately south of the Cilento coastline, a body located northwest of the Cassinis seamount and other small magnetized structures located south of the Tuscanian archipelago. In many cases, a better definition of several structures previously recognized was obtained as in the case of some tectonic alignments (e.g., the Elba ridge, the Romolo and Selli lines, etc.), a large number of igneous seamounts (e.g., Magnaghi, Marsili, Vavilov, Anchise, Quirra, Enarete, Eolo and Sisifo seamounts) and several crystalline outcrops (e.g., Ichnusa, Vercelli, M. della Rondine, Tiberino, Cassinis, Traiano, Glauco and Augusto seamounts).

Description: JCR Journal

Description: open

Description: Different methods of analysis have been applied to satellite geomagnetic data that are claimed to be representative of the crustal geomagnetic field of the Italian area. The methods are compared with each other concluding that the SCHA is the best one. The downward continuation of the field by different methods gives different results, the most realistic are those of SCHA and RHA methods. Some remarks about each method and their results for the Italian area are presented.

Description: JCR Journal

Description: open

Description: In this paper we present a correlation between volcanic structures and magnetic anomalies in the Gulf of Naples (Southern Tyrrhenian Sea) based on high resolution magnetic profiling. A densely spaced grid of magnetic profiles coupled with multichannel seismics (seismic source Watergun 15 cubic inch) was recorded in the Gulf of Naples, representing an active volcanic area during the Late Quaternary (volcanic centers of Somma-Vesuvius, Phlegraean Fields and Ischia and Procida islands). The dataset was collected during the oceanographic cruise GMS00-05 which took place during October-November 2000 in the South Tyrrhenian Sea onboard of the R/V Urania (National Research Council, Italy). Shallow volcanic structures in the subsurface of the gulf were recognized by seismo-stratigraphic analysis of high resolution profiles; the volcanic nature of some of these structures was inferred identifying the magnetic anomalies on a high resolution magnetic anomaly map of the gulf. Even if qualitative, the correlations between seismic and magnetic profiles allow us to better assess the geological structure of the Gulf of Naples.

Description: JCR Journal

Description: open

Description: An environmental investigation test site for the application of magnetic techniques to detect buried steel drums was performed in Central Italy. A magnetic survey was carried out on the area of the test site, where 12 steel drums had previously been buried. The survey was performed by means of a proton precession magnetometer for total field measurements in single sensor as well as in gradiometer configurations. The experiment has led to the definition of the magnetic signature of vertically oriented drums buried at 4.5 m below ground level. A digitally enhanced magnetic anomaly map was then produced, allowing further modelling procedures. Data reduction, processing procedures and results are presented.

Description: JCR Journal

Description: open

Description: The frequency-domain Wiener filtering was applied to magnetic anomalies in the volcanic area of Mt. Etna. This filter, under suitable conditions (additive noise, linear processing and mean-square error criterion), can furnish an effective tool for discriminating the geologic feature of interest (the signal) from the noise. The filter was first tested with synthetic data. Afterwards it was applied to a magnetic profile carried out across the principal fault system of the Mt. Etna volcano, that hosted the dykes feeding both the 1989 and the 1991-93 eruptions. The magnetic anomalies linked to the volcanic section and those linked to the contact between the clay basement and the lava coverage show significant spectral overlap. Thus by estimating the power spectrum of the signal, obtained resolving the forward problem, a least-squares Wiener filter has been designed. In such context, it was possible to verify the effectiveness of Wiener filters, whereas traditional band-pass filtering proved inadequate. In fact, analysis of the noise showed that all the meaningful components of the observed magnetic field were resolved. The results put further constraints on location and geometry of the shallow plumbing system of Mt. Etna.

Description: JCR Journal

Description: open

Description: Aeromagnetic data for Palmer Land provide new information on crustal structures of the Antarctic Peninsula. Features shown on the compilation of the Lassiter Coast and Orville Coast are characterized by systems of subparallel regional anomaly zones and lineaments. The magnetic data reveal the widespread presence of an orthogonal pattern of crosscutting linear discontinuities that can be interpreted as a Late Cretaceous/Early Tertiary fracture pattern. The main displacements in the anomaly pattern between the two units are recognized in Wetmore-Irvine glaciers area where the structure of the Antarctic Peninsula changes orientation from SW-NE to S-N. The NW-SE trending transitional zone is probably a transfer zone associated with north-westerly movement of the Lassiter Coast crustal segment relative to the Orville Coast segment. Within the Lassiter Coast a fragment of Pacific Margin Anomaly (PMA), Central Plateau Magnetic Anomaly and East Coast Magnetic Anomaly (ECMA) are mapped. Two-dimensional modelling suggests that PMA is caused by a limited depth body (8 km) consisting of numerous plutons, probably, of different ages, composition and magnetization. The Central Plateau Magnetic Anomaly and the Merrick-Sweeney-Latady zone of the Orville Coast are represented by strong positive anomaly bands that are associated with gabbro-diorite rocks and accompanying plutons intruded near by the border of Mount Poster Formation and Latady Formation. The ECMA are alignments of high-amplitude magnetic anomalies caused by gabbro-diorite bodies, which are located within the framework of the Cretaceous granite-granodiorite plutons. Granite-granodiorite plutons of Lassiter Coast Intrusive Suite are mostly reflected by positive anomalies (100-500 nT). Modelling studies and the character of distribution of the magnetic anomalies suggest that the plutons of Lassiter Coast Intrusive Suite are prominently reflected in magnetic anomalies of regional extent. The plutonic activities during the geological evolution of Palmer Land have been a more important process than what is apparent from rock outcrops. Magmatic activity abruptly diminished westward from the Behrendt Mountains apparently due to a modification of the crustal structure of the Antarctic Peninsula. The area between the Evans Ice Stream and the Behrendt Mountains is possibly underlain by the non-magnetic equivalent of the Haag Nunataks basement, similar to that which has been inferred for the Ellsworth Mountains.

Description: JCR Journal

Description: open

Description: The detection of illegal buried waste by means of geophysical techniques has recently become a major effort in shallow geophysical investigations. In particular, detection and location of underground metallic storage tanks can be accomplished using different instruments and techniques. In this paper we describe the results of an investigation carried out in a tuff quarry in Riano Flaminio (north Rome, Italy). A preliminary magnetometric survey revealed the existence of anomalous zones in the analysed region. Excavation in some of the selected areas confirmed that the anomalies were generated by underground magnetic material: over 160 steel drums were found. After their removal, a new magnetometric survey was performed. On the basis of the new map, a multifrequency induction survey, a geoelectrical profile and GPR measurements were taken to extend the characterization of the subsoil.

Description: Published

Description: JCR Journal

Description: open

Description: The space distribution of the magnetic anomaly field for the Pacific Ocean is obtained from data of the satellite MAGSAT. A number of long-wavelength magnetic anomalies of the region are identified. A spectrum analysis of a number of profiles of the anomaly field is performed disclosing typical scales of such anomalies. The wave transform of the anomaly magnetic profiles reveals and explicitly exposes the structure of the considered profile. A schematic complex cross-section is constructed, which demonstrates that the satellite data may be used in the study of the magnetic anomaly.

Description: Published

Description: JCR Journal

Description: open

Description: In recent years the analytic signal method has been of great utility in the interpretation of potential field data. The amplitude of the 3D analytic signal of magnetic data yields information on the location of the edges of the sources in both the horizontal and vertical dimensions, with the main advantage that the magnetic field and magnetic source parameters need not be known or assumed. Accurate detection of source body coordinates is becoming the main goal for interpreters and therefore enhanced techniques are acquiring an increasing revival in data interpretation. This paper presents a high-resolution approach for detecting source boundaries. These boundaries can be determined from the maxima of the analytic signal computed from the horizontal gradient of the field, defined here as a vector, the components of which are the analytic signals of x- and y-horizontal derivatives, respectively. Synthetic examples have shown the high resolving power of the proposed technique. This approach has also given very good results when applied to real data.

Description: JCR Journal

Description: open

Description: Within the framework of the GITARA II project an aeromagnetic survey was performed during the GANOVEXVII expedition (1992/1993) over the King Edward VII Peninsula in northwestern Marie Byrd Land (West Antarctica). This region which may represent the eastern flank of the Ross Sea rift system had previously been explored only at reconnaissance level. New total field and upward continued (10 km) magnetic anomaly maps are produced and interpreted here to map and discuss the crustal structure of the Edward VII Peninsula. Tworound-shaped, high-amplitude magnetic anomalies are recognised over the Alexandra Mountains block. The anomalies are difficult to interpret since susceptibility data indicate the prevalence of non-magnetic rocks at the surface. A possible interpretation is that the anomalies are due to Cretaceous mafic intrusives distinct from weakly magnetic Byrd Coast Granite of the adjacent Rockefeller Mountains block. Alternatively the anomalies could be related to buried pluton-sized Devonian Ford Granodiorite intruded by dikes. If Cretaceous in age, the former intrusives revealed from the magnetics could also be responsible for contact metamorphism of the adjacent Alexandra Mountains migmatites. Lower amplitude circular anomalies over the Central Plateau and Prestrud Inlet are likely to be caused by unexposed Devonian Ford Granodiorite which crops out in the Ford Ranges. Elongated high-frequency anomalies of the Sulzberger Bay are similar to those recognised over seismically constrained Cenozoic rift-related volcanics of the Ross Sea. A broad magnetic low over the Sulzberger Ice Shelf may be indicative of a fault bounded graben-like basin with sedimentary infill. Overall recognition of magnetic anomaly patterns and trends reveals segmentation of the Edward VII Peninsula and of the adjacent marine areas in distinct crustal blocks. Faults may separate these blocks and they are interpreted to reflect multiple Cretaceous and maybe Cenozoic crustal extension\uplift phases within this part of the West Antarctic rift system.

Description: JCR Journal

Description: open

Description: Magnetic observations made onshore the Italian Peninsula, and across the adjacent seas, have been compiled in a new digital database that provides the first complete regional scale view of the crustal scale magnetic anomalies of the region at sea level. The offshore data were acquired between 1965-1972 by the Osservatorio Geofisico Sperimentale (OGS) while the ground measurements were performed within the framework of the Progetto Finalizzato Geodinamica of the Consiglio Nazionale delle Ricerche (PFG-CNR) between 1977 and 1981. The new shaded relief magnetic anomaly map of total intensity of the Earth's magnetic field for Italy and the surrounding seas has been produced at sea level, for the geomagnetic epoch 1979.0. The most remarkable result of this new map, with respect to the previous compilations and to the aeromagnetic map of Italy, is an unprecedented view of the magnetic signature of the major tectonic elements in their regional setting. There is good correlation between known structural geology and the magnetic anomalies, and now that the longer wavelength signatures have been corrected, deeper interpretations are possible.

Description: JCR Journal

Description: open

Description: Vector measurements of the geomagnetic field have been made in the South Indian Ocean since 1988 when a Shipboard Three Component Magnetometer (STCM) was installed on board the icebreaker Shirase by the 30th Japanese Antarctic Research Expedition (JARE-30). Twelve constants related to the ship's induced and permanent magnetic field were determined by the data obtained from the JARE-30 to the JARE-35. The constants related to the ship's magnetic susceptibility distribution are almost stable throughout the cruise and mostly depend on the ship's shape. On the other hand, the constants related to the ship's permanent magnetization are variable. However, absolute values of total intensity geomagnetic field calculated from vector geomagnetic field is possible to use, if the constraints from total intensity geomagnetic field measured by the proton magnetometer and/or satellite derived magnetic anomalies are applied.

Description: JCR Journal

Description: open

Description: INTRAMAP (INtegrated Transantarctic Mountains and Ross Sea Area Magnetic Anomaly Project) is an international effort to merge the magnetic data acquired throughout the "Ross Sea Antarctic Sector" (south of 60°S between 135°-255°E) including the Transantarctic Mountains (TAM), the Ross Sea, Marie Byrd Land, and the Pacific coast, and also to begin the compilation efforts for new data over the Wilkes Basin. This project is a component of the continental scale Antarctic Digital Magnetic Anomaly Project (ADMAP). The first stage of INTRAMAP addresses the analysis and merging of GITARA (1991-1994) and GANOVEX (1984) aeromagnetic surveys together with ground magnetic data (1984-1989). The combined data sets cover an area of approximately 30 km2 over Victoria Land and adjacent Ross Sea. Map and profile gridding were implemented to integrate the data sets. These approaches are studied for improving existing strategies to adopt for the whole magnetic compilation effort. The final microlevelled grid that we produce is a new tool for regional interpretation of the main tectonic and geologic features of this sector of Antarctica.

Description: JCR Journal

Description: open

Description: A satellite magnetic anomaly map made using the POGO magnetic field data is compared to three maps made using Magsat data. A total of 14 anomalies with magnitudes greater than 3 nT can be identified in all four of the maps poleward of 60°S latitude. Forward models of the Antarctic continental and oceanic lithosphere are produced which use magnetic crustal thickness based on seismic and heat flow data, and which also use the distribution of the Cretaceous Quiet Zone from marine geophysics. These simple models can explain significant parts of eight of the 14 identified anomalies. The remaining anomalies may be caused by lateral variations of magnetization, inadequate models of the magnetic crustal thickness, or remanent magnetizations in directions other than the present field. In addition, contamination of the magnetic anomaly maps by fields of time-varying external origin (and their corresponding internal parts) is still a significant problem in the Antarctic region.

Description: JCR Journal

Description: open

Description: We show the results of the application of a new magnetic probability tomography imaging method to the aeromagnetic dataset collected by AGIP on Mt. Vesuvius in 1978. A magnetic dipole occurrence probability function is defined in such a way as to contain all information about the whole class of equivalent sources compatible with the original survey dataset. An advanced 3D visual system is also applied for the first time to visualise the spacial pattern of the magnetic dipole occurrence probability function. It is shown that in the case of Vesuvius, the shallow plumbing system is characterised by a high probability of occurrence of a dipole at 2 km of depth b.s.l., nearly directed along the present main earth’s magnetic field. This leads to hypothesize that the top terminal portion of the volcanic apparatus is completely filled with magnetised volcanic material.

Description: Published

Description: JCR Journal

Description: open

Description: The time-correlation properties in the hourly time variability of volcano-magnetic data measured at the active volcano Mt. Etna, Sicily (southern Italy), are investigated by using the detrended fluctuation analysis (DFA). DFA is a data processing method that allows for the detection of scaling behaviors in observational time series even in the presence of nonstationarities. The procedure adopted has revealed unambiguous link between the dynamics of the measured data and the recent eruptive episode of the volcano occurred on October 27, 2002.

Description: Published

Description: 1921-1929

Description: partially_open

Description: Remarkable changes in the local magnetic field were associated with the onset of the 2002–2003 flank eruption at Mt. Etna. After differential magnetic field measurements were filtered from the external noise by using adaptive filters, we recognized two stages in the total intensity changes, which are closely related to different volcanic events: (a) rapid variations of about 4–5 nT associated with October 26 seismic swarm recorded beneath the summit craters; (b) step-like variations of 9–10 nT coincident with October 27 eruptive fissures opening up in the north flank. These observations are generally consistent with those calculated from simple magnetic models of these volcanic processes, in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth. The magnetic data not only allow the timing of the intrusive event to be described in greater detail but also, together with other volcanological and geophysical evidences, permit some constraints to be set on the characteristics of propagation of a shallow dike. Firstly, at around midnight on 26 October magma was rapidly injected to a depth of 3–4 km just below the summit craters. Secondly, after 1:00 on 27 October, continued intrusion magma occurred upward and culminated a few hundred meters below the free surface fractured along a N–E direction. Thirdly, at about 2:28, magma gave rise to an explosive fissural vent at the northern base of the NE crater near 3000 m a.s.l. Finally, at about 5:00, the first eruptive fissure became active along the eastern border of the NE rift at 2500 m a.s.l. The rate of growth of the magnetic anomalies, moreover, leads to the interpretation that the magmatic intrusion travelled northward from base of the NE crater to the NE rift at approximately 14 m/min.

Description: Published

Description: 1-14

Description: partially_open