scholarly journals GDS (Geomagnetic Depth Sounding) in Italy: applications and perspectives

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
D. Di Mauro ◽  
E. Armadillo ◽  
E. Bozzo ◽  
V. Cerv ◽  
A. De Santis ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Transfer Functions ◽  
Central Italy ◽  
Geophysical Methods ◽  
Geomagnetic Variations ◽  
Conductivity Distribution ◽  
Marginal Areas ◽  
Mountain Chain ◽  
Conducting Bodies ◽  
Depth Sounding

The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity contrasts within the Earth. Lateral resolution of outlined patterns depends on the array dimensions and density of measurement sites over the investigated area. The inspection depth is constrained by the period of geomagnetic variations considered in data processing. Regions with significant geological features such as boundaries of continental plates, marginal areas of contact between tectonic units or other geodynamical processes, are of primary interest for the application of the MagnetoVariational (MV) method. In the last ten years, in the frame of the ElectroMagnetic (EM) sounding techniques in applied geophysics, this method has been applied in Italy by researchers of the Istituto Nazionale di Geofisica, Rome, the Dipartimento di Scienze della Terra, Universitá di Genova and the Czech Science Academy of Prague. The Ivrea body in the Northwestern Alps and their junction with the Apennine chain, the micro-plate of the Sardinian-Corsican system and, recently, the central part of the peninsula along Tyrrhenian-Adriatic lithospheric transects were investigated. Studies in time and frequency-domain used in the first investigations, have been followed by more refined analysis involving tests on the induced EM field dimension, computations of single site Transfer Functions (TFs) through Parkinson arrows' and Fourier maps in the Hypothetical Event technique (HE). It was possible to describe the electrical conductivity distribution in the inner part of the SW Alpine arc and to confirm the presence of lithospheric and asthenospheric anomalies obtained by other geophysical methods. For the Sardinia-Corsica system, 2D and 3D inversion models highlighted the existence of two major conducting bodies, one north of Corsica, and the other south of Sardinia. In Central Italy, the regional electrical conductivity distribution pointed out a deep conductive structure beneath the Apennines and a very resistive root for this part of the mountain chain.

Joint inversion of magnetotelluric tippers and geomagnetic depth sounding transfer functions constrains electrical conductivity beneath islands

2021 ◽  
Author(s):  
Chaojian Chen ◽  
Mikhail Kruglyakov ◽  
Rafael Rigaud ◽  
Alexey Kuvshinov
Keyword(s):  
Electrical Conductivity ◽  
Transfer Functions ◽  
Joint Inversion ◽  
Optimization Method ◽  
Induction Effect ◽  
Period Range ◽  
Covariance Matrix Adaptation ◽  
Conductivity Structure ◽  
Multiple Data Sets ◽  
Depth Sounding

<p>Geomagnetic field variations recorded at island geomagnetic observatories are one of the data sources that can be used to constrain the electrical conductivity beneath oceans. Hitherto, magnetotelluric (MT) tippers (period range from a few minutes to 3 hours) and geomagnetic depth sounding (GDS) transfer functions (TFs; period range from 6 hours to a few months) were inverted separately to reveal the electrical conductivity structure underneath island observatories.  In this study, we develop a quasi 1-D tool to simultaneously invert MT tippers and GDS TFs. To account for source complexity, we resort to GDS TFs that relates a set of spherical harmonics coefficients describing the source (of ionospheric or magnetospheric origin) to a locally measured vertical magnetic field component. Joint inversion of multiple data sets from different sources helps to improve vertical resolution and reduce uncertainties in the recovered conductivity models. The stochastic optimization method, known as Covariance Matrix Adaptation Evolution Strategy, is applied to solve the inverse problem. The term “quasi” is used here to stress the fact that during 1-D inversion the 3-D forward modeling operator is exploited to account for the ocean induction effect (OIE), which is known to strongly influence the island electromagnetic (EM) responses. To efficiently model MT tippers and GDS TFs, the Cartesian-to-Cartesian and spherical-to-Cartesian 3-D EM modeling engines, based on a nested integral equation approach, are adopted. We apply the developed tool to jointly invert MT tippers and GDS TFs estimated at Honolulu geomagnetic observatory, located at Oahu island (Hawaii) in Pacific Ocean, and discuss the recovered conductivity structure.</p>

scholarly journals Geology and geophysics at the archeological park of Vulci (central Italy)

2014 ◽  
Vol 57 (1) ◽  
Author(s):  
Marco Marchetti ◽  
Vincenzo Sapia ◽  
Adriano Garello ◽  
Donatella De Rita ◽  
Alessandra Venuti
Keyword(s):  
Electrical Resistivity ◽  
Magnetic Susceptibility ◽  
Cultural Heritage ◽  
Central Italy ◽  
Geophysical Methods ◽  
Archaeological Sites ◽  
Local Authorities ◽  
Resistivity Tomography ◽  
Geological Information ◽  
Geological Map

<p>The Vulci archeological site was object of interest by the Soprintendenza ai beni culturali dell’Etruria meridionale (Italian government department responsible for southern Etruria’s cultural heritage) since the beginning of the 20th century. In 2001, the Ministero dei Beni Culturali (Italian ministry of cultural heritage) along with the local authorities, opened a natural-archeological park. In this area, it lies most of the ancient Etruscan city of Velch (today known by its Latin name, Vulci) including the Osteria Necropolis that is the object of this study. Recently, new archaeological excavations were made and the local authorities needed major geological information about the volcanic lithotypes where the Etruscans used to build their necropolis. The aim of this study is to define the geological and geophysical characteristics of the rock lithotypes present in the Vulci park. For this purpose, a geological map of the area (1:10000) has been realized. Moreover, two different geophysical methods were applied: measurements of magnetic susceptibility and electrical resistivity tomography. Magnetic susceptibility analyses clearly identify magnetic contrasts between different lithotypes; the characteristics of the pyroclastic flow that originated the Sorano unit 2 and its vertical facies variations are well recorded by this parameter that along with lithostratigraphic observations provides information about the depositional conditions. Two electrical resistivity tomographies were performed, which show the Sorano unit 2 thickness to be of c. 7 m with resistivity values ranging from 200 to 400 Ω·m. This kind of multidisciplinary approach resulted to be suitable to study this type of archaeological sites, revealing that areas characterized by a relevant thickness and wide areal extension of volcanic lithotypes can be a potential site where Etruscans might have excavated their necropolis.</p>

Chasing the Magma Chamber: MT meets Geodynamics and Seismology – A numerical case study of magmatic plumbing at Oldoinyo Lengai Volcano

2021 ◽  
Author(s):  
César Daniel Castro ◽  
Miriam Christina Reiss ◽  
Arne Spang ◽  
Philip Hering ◽  
Luca de Siena ◽  
...  
Keyword(s):  
Magma Chamber ◽  
Transfer Functions ◽  
Geophysical Methods ◽  
Gravity Anomalies ◽  
Active Volcano ◽  
Rift System ◽  
East African Rift System ◽  
Plumbing System ◽  
East African ◽  
Oldoinyo Lengai

&lt;p&gt;How well can geophysical methods image magmatic systems? Geophysical methods are commonly used to image magmatic systems; however, synthetic studies which give insights into the resolution of such methods and their interpretational scope are rare. Gravity anomalies, magnetotelluric, seismological and geodynamical modelling all have a different sensitivity to the rock parameters and are thus likely complementary methods. Our study aims to better understand their interplay by performing joint modelling of a synthetic magmatic system. &amp;#160;Our model setup of a magma chamber is inspired by seismological observations at the Natron plumbing system including active volcano Oldoinyo Lengai within the East African Rift system. The geodynamic modelling is guided by shear-wave velocity anomalies and it is constrained by a large Bouguer gravity anomaly which is modelled by a voxel-based gravity code. It yields the 3D distribution of several geological parameters (pressure, temperature, stress, density, rock type). The parameters are converted into a 3D resistivity distribution. By 3D forward modelling including the topography, synthetic MT transfer functions (phase tensor, induction vectors) are calculated for a rectangular grid of 441 sites covering the area. The variation of geodynamic parameters and/or petrological relations alters the related resistivity distribution and thus yields the sensitivity of MT responses to geodynamic parameters. In turn, MT observations may constrain geodynamic modelling by inverting MT transfer functions. The inversion is performed allowing for the recent seismicity distribution beneath the Natron plumbing system, assuming that active seismic areas are related to enhanced resistivity. The inversion is performed for a realistic distribution (in view of logistic accessibility) of about 40 MT sites.&lt;/p&gt;&lt;p&gt;By combining multiple forward models, this study yields insights into the sensitivity of different observables and thus provides a valuable base on how MT, gravity and seismological observations can help imaging a complex geological setting.&lt;/p&gt;

The reduction of source effect for reliable estimation of geomagnetic transfer functions

2020 ◽  
Vol 221 (1) ◽  
pp. 415-430
Author(s):  
Tomasz Ernst ◽  
Krzysztof Nowożyński ◽  
Waldemar Jóźwiak
Keyword(s):  
Magnetic Field ◽  
Transfer Functions ◽  
Negative Impact ◽  
Vertical Component ◽  
Regional Effect ◽  
Geomagnetic Variations ◽  
Source Effect ◽  
Original Algorithm ◽  
Induction Components ◽  
The Time Domain

SUMMERY We have analysed the literature suggestions regarding possible changes in vertical magnetic transfer function (VTF) over time. We have shown that for periods above 1500 s the observed changes in VTF are caused by the source effect and we proposed how to reduce this negative impact. For calculations we used 1-min recordings of geomagnetic variations registered between 2002 and 2017 in various geomagnetic observatories. In data processing we used frequency-domain Egbert's algorithm and our original algorithm based on the method of least squares in the time domain for some comparisons and tests. We have shown that for periods over 1500 s the VTFs calculated separately from summer and winter data are different. However, our analysis shows that the variability of the VTF values obtained is misleading and results from time-changing presence of magnetic field variations that do not fulfill the assumption of plane wave (there is a vertical component in the incident magnetic field). These variations are much more numerous in summer than in winter. More detailed analysis has shown also that they are usually small at night and big during the day. The vertical components of these variations constitute an error correlated with input signals (horizontal components), which alters the values of the determined VTF. Furthermore, error bars do not take this effect into account. It makes it impossible to improve the accuracy of calculations by increasing the amount of data. Analysing the estimated external parts of vertical components from the Central European observatories we noticed a great similarity of these signals even if the induction components were clearly different, which indicates that this is a regional effect. On this basis, we proposed a procedure to improve the accuracy of VTF determination by means of pre-selection of data.

INVESTIGATIONS DURING 1962 OF THE ALERT ANOMALY IN GEOMAGNETIC VARIATIONS

1963 ◽  
Vol 41 (11) ◽  
pp. 1868-1882 ◽  
Author(s):  
L. K. Law ◽  
J. DeLaurier ◽  
F. Andersen ◽  
K. Whitham
Keyword(s):  
Electrical Conductivity ◽  
Bouguer Anomaly ◽  
Thermal Anomaly ◽  
Infinite Cylinder ◽  
Range Data ◽  
Geomagnetic Variations ◽  
Cylindrical Model ◽  
Field Response ◽  
Variation Vector ◽  
Simple Potential

Magnetic variations measured at three stations across the strike of the anomaly in electrical conductivity of the earth's mantle suggested by Whitham and Andersen (1962) near Alert, Ellesmere Island, have been analyzed by simple potential theory. The anomalous internal contributions to the magnetic variation vector show striking confinement consistent with an underground current in a northeast–southwest direction at a depth between 50 and 70 km, a few kilometers southeast of Alert. If the anomalous conductor is approximated by a uniform infinite cylinder, the horizontal field response as a function of frequency can then be explained with a conductivity of [Formula: see text] e.m.u. and a cylindrical radius of about 50 km. The vertical field response is, however, an unsatisfactory fit to this model. A possible asymmetry is noted based on the hourly range data: this could be explained by the dipping of the real conductor under Ellesmere Island.Preliminary earth potential measurements show that, as expected, the electric field variations are abnormally low at Alert.The gravitational consequences of the cylindrical model are discussed and compared with two profiles from the same region. A Bouguer anomaly is found in the predicted region if certain regional gradients are assumed, but its magnitude is smaller than that predicted from the cylindrical model in hydrostatic equilibrium. It is clear that approximate agreement can be obtained with crustal thinning of some 20 km.The significance of the thermal anomaly thought to be responsible for the electrical conductivity anomaly is discussed briefly.

Electrical conductivity at mid-mantle depths estimated from the data of Sq and long period geomagnetic variations

2011 ◽  
Vol 55 (2) ◽  
pp. 241-264 ◽  
Author(s):  
Oldřich Praus ◽  
Jana Pěčová ◽  
Václav Červ ◽  
Svetlana Kováčiková ◽  
Josef Pek ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Geomagnetic Variations ◽  
Long Period

A Transfer Function Analysis of a Geomagnetic Depth Sounding-Profile across Central British Columbia

1973 ◽  
Vol 10 (7) ◽  
pp. 1089-1098 ◽  
Author(s):  
H. Dragert
Keyword(s):  
British Columbia ◽  
Transfer Functions ◽  
Function Analysis ◽  
Three Dimensional ◽  
Vertical Component ◽  
Rocky Mountain ◽  
Three Dimensional Model ◽  
Transfer Function Analysis ◽  
Single Station ◽  
Depth Sounding

Time variations of the geomagnetic field observed across British Columbia at a mean latitude of 54 °N are analyzed using 'single-station' and 'paired-station' optimum transfer functions. The frequency and spatial dependence of both coastal and inland geomagnetic anomalies are estimated with the following results. (1) The normal coast effect is strongly perturbed by lateral conductivity inhomogeneities both north and south of the profile. (2) A simple, single NW–SE striking conductivity contrast between the Cordillera and plains cannot account for the total geomagnetic anomaly in the area of the Rocky Mountain Trench; a three-dimensional model is required, incorporating (i) a lateral inhomogeneity striking east–west and located to the south of the profile, (ii) the effect of induction by the vertical component of source or secondary fields.

scholarly journals Physicochemical Properties of Honey from Marche, Central Italy: Classification of Unifloral and Multifloral Honeys by Multivariate Analysis

2014 ◽  
Vol 9 (11) ◽  
pp. 1934578X1400901 ◽  
Author(s):  
Cristina Truzzi ◽  
Silvia Illuminati ◽  
Anna Annibaldi ◽  
Carolina Finale ◽  
Monica Rossetti ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Physicochemical Properties ◽  
Robinia Pseudoacacia ◽  
Central Italy ◽  
Physicochemical Characterization ◽  
Castanea Sativa ◽  
Principal Component ◽  
Pattern Recognition Methods ◽  
Multifloral Honey

The purpose of this study was the physicochemical characterization and classification of Italian honey from Marche Region with a chemometric approach. A total of 135 honeys of different botanical origins [acacia ( Robinia pseudoacacia L.), chestnut ( Castanea sativa), coriander ( Coriandrum sativum L.), lime ( Tilia spp.), sunflower ( Helianthus annuus L.), Metcalfa honeydew and multifloral honey] were considered. The average results of electrical conductivity (0.14 – 1.45 mS cm−1), pH (3.89 – 5.42), free acidity (10.9 – 39.0 meqNaOH kg−1), lactones (2.4 – 4.5 meqNaOH kg−1), total acidity (14.5 – 40.9 meqNaOH kg−1), proline (229–665 mg kg−1) and 5-(hydroxy-methyl)-2-furaldehyde (0.6–3.9 mg kg−1) content show wide variability among the analysed honey types, with statistically significant differences between the different honey types. Pattern recognition methods such as principal component analysis and discriminant analysis were performed in order to find a relationship between variables and types of honey and to classify honey on the basis of its physicochemical properties. The variables of electrical conductivity, acidity (free, lactones), pH and proline content exhibited higher discriminant power and provided enough information for the classification and distinction of unifloral honey types, but not for the classification of multifloral honey (100% and 85% of samples correctly classified, respectively).

3D imaging of the subsurface electrical conductivity structure in West Bohemia covering mofettes and Quaternary volcanic structures by using magnetotellurics

2020 ◽  
Author(s):  
Anna Platz ◽  
Ute Weckmann ◽  
Josef Pek ◽  
Svetlana Kováčiková ◽  
Radek Klanica ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Transfer Functions ◽  
Earthquake Swarm ◽  
Rift System ◽  
Target Area ◽  
The South ◽  
3D Inversion ◽  
Data Set ◽  
Eger Rift ◽  
Conductive Channel

&lt;p&gt;The West Bohemian Massif represents the easternmost part of the geo-dynamically active European Cenozoic Rift System. This region hosts different tectonic units, the NE-SW trending Eger Rift, the Cheb Basin and a multitude of different faults systems. Furthermore, the entire region is characterised by ongoing magmatic processes in the intra-continental lithospheric mantle. These processes take place in absence of active volcanism at surface, but are expressed by a series of phenomena, including e.g. the occurrence of repeated earthquake swarms and massive degassing of CO&lt;sub&gt;2&lt;/sub&gt; in the form of mineral springs and mofettes. Active tectonics is mainly manifested by Cenozoic volcanism represented by different Quaternary volcanic structures e.g. the Eisenb&amp;#252;hl, the Kammerb&amp;#252;hl and different maars. All these phenomena make the Eger Rift a unique target area for European intra-continental geo-scientific research. Therefore, an interdisciplinary drilling programme advancing the field of earthquake-fluid-rock-biosphere interaction was funded within the scope of the ICDP. Magnetotelluric (MT) measurements are applied to image the subsurface distribution of the electrical conductivity from shallow surface down to depths of several tens of kilometres. The electrical conductivity is a physical parameter that is particularly sensitive to the presence of high-conductive phases such as aqueous fluids, partial melts or metallic compounds. First MT measurements within this ICDP project were carried out in winter 2015/2016 along two 50 km long perpendicular profiles with 30 stations each and a denser grid of 97 stations close to the mofettes with an extension of 10 x 5 km&lt;sup&gt;2&lt;/sup&gt;. Mu&amp;#241;oz et al. (2018) presented 2D images along the NS profile of one regional profile. They reveal a conductive channel at the earthquake swarm region that extends from the lower crust to the surface forming a pathway for fluids into the region of the mofettes. A second conductive channel is present in the south of the model. Due to the given station setup, the resulting 2D inversion allows ambiguous interpretations of this feature. 3D MT data and inversions are required to distinguish between different scenarios and to fully describe the 3D structure of the subsurface. Therefore, we conducted a large MT field experiment in autumn 2018 by extending the study area towards the south. Broad-band MT data were measured at 83 stations along three 50-75&amp;#160;km long profiles and some additional stations across the region of the maars, the Tachov fault and the suture zone allowing for 2D as well as 3D inversion on a crustal scale. To improve the data quality, advanced data processing techniques were applied leading to good quality transfer functions. Furthermore, the previously collected MT data were reprocessed using the new approaches. This entire MT data set across the Eger Rift environment together with old MT data collected within the framework of the site characterisation in the surrounding of the KTB drilling are used to compute 3D resistivity models of the subsurface, with combining different transfer functions. These 3D inversion results will be introduced and discussed with regard to existing geological hypotheses.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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