scholarly journals Acquisition procedures, processing methodologies and preliminary results of magnetic and ROV data collected during the TOMO-ETNA experiment

2016 ◽  
Vol 59 (4) ◽  
Author(s):  
Danilo Cavallaro ◽  
Luca Cocchi ◽  
Mauro Coltelli ◽  
Filippo Muccini ◽  
Cosmo Carmisciano ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Structural Features ◽  
Magnetic Survey ◽  
Remotely Operated Vehicle ◽  
Ne Sicily ◽  
Mt Etna ◽  
Source Study ◽  
Anomaly Map

<p>The TOMO-ETNA experiment was devised for the investigation of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands, through an active source study. In this experiment, a large amount of geophysical data was collected both inland and in the Ionian and Tyrrhenian Seas for identifying the major geological and structural features offshore Mt. Etna and NE Sicily. One of the oceanographic cruises organized within the TOMO-ETNA experiment was carried out on the hydrographic vessel “Galatea” by Italian Navy. During the cruise a detailed magnetic survey and a set of ROV (remotely operated vehicle) dives were performed offshore Mt. Etna. The magnetic survey allowed the compilation of a preliminary magnetic map revealing a clear direct relationship between volcanic structures and high frequency magnetic anomalies. Significant positive magnetic anomalies were identified offshore the Timpa area and along the easternmost portion of the Riposto Ridge <span>and</span> correlated to a primitive volcanic edifice and to shallow volcanic bodies, respectively. On the whole, the magnetic anomaly map highlights a clear SW-NE decreasing trend, where high amplitude positive magnetic anomaly pattern of the SW sector passes, northeastwardly, to a main negative one. ROV dives permitted to directly explore the shallowest sectors of the Riposto Ridge and to collect several videos and seafloor samples, allowing us to identify some locally developed volcanic manifestations.</p>

Analysis of the Czech magnetic anomaly data obtained by ground-based and airborne magnetic surveys

2020 ◽  
Author(s):  
Pavel Hejda ◽  
Dana Čápová ◽  
Eva Hudečková ◽  
Vladimír Kolejka
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Data File ◽  
Ore Deposits ◽  
Substantial Contribution ◽  
Magnetic Survey ◽  
Contour Maps ◽  
Anomaly Map ◽  
Ground Magnetic ◽  
Airborne Survey

&lt;p&gt;The modern epoch of ground magnetic surveying activity on the Czech territory was started by the Institute of Geophysics by setting up a fundamental network of the 1&lt;sup&gt;st&lt;/sup&gt; order in 1957-58. It consists of 199 points and was reoccupied in 1976-78 and 1994-96. The anomaly maps were constructed by subtraction of the IGRF model.&lt;/p&gt;&lt;p&gt;Extensive aeromagnetic measurements have been performed from 1959 to 1972 by permalloy probe of Soviet provenience. The accuracy of the instrumentation was about (and often above) 10 nT. The second period of airborne survey started in 1976. Thanks to the deployment of proton precession magnetometer, the accuracy improved to ~ 2 nT. Since 2004 the measurements were carried out by caesium magnetometer. The data were digitized, known anthropogenic anomalies were cleared away and data were transformed to the regular grid with step 250 m. The final data file of magnetic anomalies &amp;#916;T, administered by the Czech Geological Survey, represents a substantial contribution to the exploration of ore deposits and to the structure geology in general.&lt;/p&gt;&lt;p&gt;In view of the fact that data file of magnetic anomalies was compiled from data acquired by heterogeneous methods in the course of more than 50 years, our recent study is aimed at looking into the homogeneity of the data by comparison them with ground-based magnetic survey. A simple comparison of the contour maps showed good similarity of the large regional anomalies. For more detailed analysis, the variation of &amp;#916;T in the neighbourhood of all points of the fundamental network was inspected and the basic statistic characteristics were computed. Summary results as well as several examples will be presented accordingly as the INSPIRE compliant services and eventually as the user-friendly web map application and made available on the CGS Portal http://mapy.geology.cz/ and on the updated web of the CzechGeo/EPOS consortium www.czechgeo.cz. Incorporating the map into the World Digital Magnetic Anomaly Map (WDMAM &amp;#8211; IAGA) is also under consideration. This data will also be interesting for the EPOS.&lt;/p&gt;

scholarly journals Chapala half-graben structure inferred. A magnetometric study

2015 ◽  
Vol 54 (4) ◽  
Author(s):  
Miguel Angel Alatorre-Zamora ◽  
José Oscar Campos-Enríquez ◽  
José Guadalupe Rosas-Elguera ◽  
Laura Peña-García ◽  
Roberto Maciel-Flores ◽  
...  
Keyword(s):  
Late Miocene ◽  
Large Scale ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Magnetic Survey ◽  
Structural Studies ◽  
General Terms ◽  
Extensional Tectonic ◽  
Half Graben ◽  
Structural High

Many geologic and tectonic-structural studies refer to the Chapala lake structure in general terms as a graben (or more generally as rift). However, no formal study has addressed its structure. The Chapala Lake is located in a major topographic depression surrounded by broad middle to late Miocene volcanic-capped plateaus. We conducted a magnetic survey comprising five S-N lines crossing the Chapala Lake. One profile comprises a land extension (southwards along roads). Magnetic anomalies obtained are mainly smooth and large scale features associated to the sedimentary infill, local and high amplitude anomalies are due to shallow basaltic and andesitic tilted blocks, and highest amplitudes due to the outcropped basaltic flows of the Los Alacranes and Mezcala islands. The models obtained point to a large structural high located at the central depression portion that separates two structural lows. The structural lows correspond to half-graben type structures. Through the faults delimiting it were emplaced the basaltic flows of the Mezcala and Los Alacranes islands. The presence of half-graben type structures indicates that the crust has been subject to an extensional tectonic.

REPORT OF THE SEG COMMITTEE FOR A NATIONAL MAGNETIC ANOMALY MAP

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 1055-1055
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Developed Countries ◽  
Magnetic Survey ◽  
Accurate Representation ◽  
Anomalous Magnetic Field ◽  
Anomaly Map ◽  
The U.S ◽  
Airborne Magnetic ◽  
Airborne Magnetic Survey

Our country’s urgent need to find new sources for minerals and energy and its need to know more about the planet on which we live could be greatly assisted by preparation of a national magnetic anomaly map (NMAM)—a map which will provide an accurate representation of the earth’s anomalous magnetic field. It is startling to note that the U.S. is one of the few developed countries which has not commissioned a detailed airborne magnetic survey of the whole country, followed by production of a national magnetic anomaly map.

Regional Magnetic Anomalies and Geology in Fennoscandia: A discussion

1972 ◽  
Vol 9 (3) ◽  
pp. 219-232 ◽  
Author(s):  
R. P. Riddihough
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Fracture Zones ◽  
West Central ◽  
Anomaly Map ◽  
The Baltic

A contoured magnetic anomaly map constructed from aeromagnetic profiles reflects the established tectonic patterns of the Fennoscandian region and permits speculations about such features as continental discontinuities colinear with oceanic fracture zones. An interpretation of the most outstanding magnetic anomaly of the region, in west-central Sweden, shows that its source is associated with a Precambrian anorogenic complex and has an unusually high magnetization. Magnetic similarities between the Baltic and Canadian shields are briefly discussed.

3D forward and inverse modeling of total-field magnetic anomalies caused by a uniformly magnetized layer defined by a linear combination of 2D Gaussian functions

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. L11-L18 ◽  
Author(s):  
Juan García-Abdeslem
Keyword(s):  
Linear Combination ◽  
Magnetic Anomaly ◽  
Synthetic Data ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Nonlinear Inversion ◽  
Total Field ◽  
Gaussian Functions ◽  
Estimated Parameters ◽  
Forward And Inverse Modeling

I develop a method for 3D forward modeling and nonlinear inversion of the total-field magnetic anomaly caused by a uniformly magnetized layer with its top and bottom surfaces represented by a linear combination of 2D Gaussian functions. The solution of the forward problem is found through both analytic and numerical methods of integration to calculate the theoretical magnetic anomaly. The magnetic anomalies computed by the present numerical method compare well with the ones calculated by using an analytic solution. To test the robustness of the algorithm, the inversion is performed with noisy synthetic data. The estimated parameters in the case of a synthetic model were found to deviate only modestly from the true parameters in the presence of noise. The algorithm is used to interpret a dipolar magnetic anomaly of high amplitude attributable to a laccolith of intermediate composition in northern Mexico.

Kimberlites and exploration geophysics

Geophysics ◽  
1979 ◽  
Vol 44 (8) ◽  
pp. 1395-1416 ◽  
Author(s):  
James C. Macnae
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
Magnetic Survey ◽  
Emplacement Mechanism ◽  
Geophysical Technique ◽  
Geologic Model ◽  
Main Factors ◽  
Original Size ◽  
Large Survey

This paper discusses geophysical prospecting techniques for kimberlite pipes, a major source of diamonds. A simple geologic model based on descriptions by Hawthorne (1975) and Nixon (1973) is given, and the varied geophysical responses obtained over kimberlite pipes are interpreted in terms of this model. The three main factors controlling these responses are the original size and inhomogeneity of the pipe, the depth of erosion, and the degree of weathering. Kimberlite pipes are roughly elliptical in surface exposure in most cases, with a “carrot shaped” extension at depth. The unweathered portion of the pipe generally contains a few percent magnetite, and this in most cases produces a clearly detectable magnetic anomaly. The presence of deep weathering may alter the magnetite in the top of the pipe to nonmagnetic oxides of iron, thus resulting in an increased depth to the magnetic source. If this depth is large, the magnetic response may not be large enough to detect the kimberlite in the presence of noise and the effect of other structures. In addition, if little erosion has taken place since emplacement, kimberlitic sediments known as epiclastic kimberlite will be present to considerable depths in the pipe, and this may also lead to the absence of a clear magnetic anomaly. In one large survey in South Africa, electromagnetic (EM) techniques have proven to be remarkably effective in detecting the presence of weathered clays or epiclastic kimberlite contained within the pipes. All pipes discovered during this survey had unmistakable EM signatures, while five out of eight had very small magnetic anomalies which would not likely have been selected as potential targets on the basis of magnetic data alone. These examples would indicate that in any area where deep weathering is expected, an EM survey is essential in combination with a magnetic survey if reconnaissance is to be based on airborne geophysical techniques. Due to the emplacement mechanism of kimberlite, considerable inhomogeneity within a pipe may be present, leading to significant variation in the response of any geophysical technique to one pipe, with resultant interpretation difficulties. Although this is not a limitation in the discovery of new pipes, it does make their geophysical delimitation difficult.

Intermediate‐scale magnetic anomalies of the Earth

Geophysics ◽  
1985 ◽  
Vol 50 (12) ◽  
pp. 2817-2830 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
D. W. Strangway
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Anomaly ◽  
Correlation Coefficients ◽  
Sedimentary Basins ◽  
Magnetic Anomalies ◽  
The Earth ◽  
Asymmetric Component ◽  
Anomaly Map ◽  
Well Correlation

Four separate magnetic anomaly maps of the earth are derived from magnetometer satellite data acquired at dawn and at dusk using two different altitude ranges. The magnetic anomalies on the two dawn maps (or dusk maps) are well correlated for spherical harmonics of degree less than 51, suggesting that the time varying external magnetic field and leveling noise have negligible effects on these harmonics. Dawn and dusk maps have an appreciable asymmetric component for harmonics of degree n ⩽ 5 and n = 15 and 17, arising from the quasi‐stable external magnetic field. Dawn‐dusk covariant harmonics of degree [Formula: see text] with signal‐to‐noise ratios greater than 1.5 correlate well. Correlation coefficients are higher than 0.75, implying that these harmonics can be repeatably derived. A global scalar magnetic anomaly map is derived based on these harmonics. The map is then converted to a magnetic susceptibility anomaly map by an inversion technique. The susceptibility anomalies delineate the ocean‐continent differences as well as the boundaries of tectonic provinces, modern uplifts, crustal rifts, and sedimentary basins.

scholarly journals Mapping and interpretation of satellite magnetic anomalies from POGO data over the Antarctic region

1999 ◽  
Vol 42 (2) ◽  
Author(s):  
M. E. Purucker ◽  
R. R. B. von Frese ◽  
P. T. Taylor
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Oceanic Lithosphere ◽  
Crustal Thickness ◽  
Time Varying ◽  
Antarctic Region ◽  
Magnetic Field Data ◽  
Anomaly Map ◽  
The Antarctic ◽  
Lateral Variations

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.

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