The Use of ERT, Magnetic and EM High Resolution Methods in Archeological Sites - A Case Study in Apollonia, Albania
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During the period 2011-2012, high resolution geoelectric surveys using Electrical Resistance Tomography (ERT), Magnetic and Electromagnetic surveys, has been carried on three archeological sites of Bylis, Apollonia and Tirana Castle, Albania. The geoelectric surveys of squares, was carried out with 2D ERT parallel profiles with distance between them 1.5m or 2m and the distance between electrodes 1m where a multicore cable with 30 takeouts was used. The squares have been surveyed using two geometric configurations, Wenner and Schlumberger arrays. The EM survey grid is 1x 0.5m, whereas the magnetic grid is 1x1m. A 3D interpretation of resistivity profiles has been carried out and the resistivity distribution maps of different depths have been taken. At the same time the 2D map of magnetic anomalies is taken after the appropriate diurnal corrections. The EM 3D maps, show the ground scanning of the conductivity of the underground. From this study we conclude that the ERT method delineates very well the thickness of cultural layer and the buried archaeological objects inside it where the anomalies taken correspond with magnetic anomalies, whereas the EM method delineates very well the conductive clays from the other surrounding formations.Keywords:
Electrical Resistivity Tomography
Magnetic survey
Square (algebra)
The major part of this thesis is a description of a magnetic survey of part of the Kilklvan district in south east Queensland. The outcrop is poor, so that a regional magnetic survey was undertaken in an attempt to define the geological boundaries between the major rock types, and to locate Magnetic anomalies that could be investigated in more detail. A total of 1068 magnetic stations was occupied in the regional survey. The magnetic values were contoured with an interval of 200 gammas and are presented as an overlay drawn to the same scale as the geological map.ln general the Triassic and Palaeozoic rocks have a contrasting magnetite content, so that the boundaries between the two are reflected in the regional magnetic contour map. A number of well defined magnetic anomalies were located in the area, most of which could be correlated with outcropping rocks that have a high magnetite content.Several areas were selected for a more detailed study, and a further 1010 magnetic stations were located along traverses across the anomalies found in the regional survey. This close survey indicated that the detailed geology of the area is exceedingly complex, and in only one case was a quantitative interpretation of the magnetic anomalies attempted.A method was developed for the interpretation of Magnetic anomalies over a dipping contact. The mathematical formulation of the problem was derived from first principles, and the final solutions evaluated using the G.E. 225 computer. The output from the computer is in the form of tables that have general application and which should be of value to geologists for the solution of structural problems.A geological map was drawn using as control the surface exposures and the regional magnetic contour map. A great variety of Palaeozoic and Triassic rock types exists in the area. These have been described; of particular interest is the occurrence of a glaucophane rock containing pumpellyite.
Magnetic survey
Outcrop
South east
Geological survey
Contour line
Geophysical survey
Aeromagnetic survey
Geologic map
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By surface high- precision magnetic survey,magnetite is explored in the target area where large Quaternary system covered. The up and down continuation magnetic anomaly magnetic survey data of different height are calculated,according to the magnetic anomaly distribution features,magnetic parameter physical property and geologic condition,8 magnetic anomaly in this area are determined. When the value is more than500 n T,it's inferred it caused by magnetic anomaly. According to the normal magnetic distribution,some drills are arranged to test in the C1 normal magnetic anomaly area and other normal magnetic anomaly area.The magnetite was not found only in few drilling holes,the successful example is gotten which exploration by surface magnetic method,affords experience for other area with the same geologic background.
Magnetic survey
Anomaly (physics)
Rock magnetism
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A result of an aeromagnetic survey in an area of northeast Japan is reported, and some magnetic anomalies found by this survey are discussed, particularly a remarkable magnetic anomaly in the North Miyagi district that was not anticipated on the basis of surface geology.
Aeromagnetic survey
Magnetic survey
Anomaly (physics)
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During 1978 and 1979 the Bureau of Mineral Resources investigated the characteristics of the magnetic anomaly at Elura by a program of airborne, ground, carborne, and down-hole magnetic surveys, and laboratory magnetic measurements on core samples.The results of this work show that the magnetic anomaly at Elura is caused mainly by a remanently magnetised pyrrho-titic zone within the Elura deposit. However, near-surface magnetic sources contribute to the anomaly at low altitudes.Spectral analyses of airborne and carborne magnetic data at Elura indicate that the effects of near-surface and bedrock magnetic sources can be separated by careful attention to data acquisition and filtering.
Magnetic survey
Anomaly (physics)
Bedrock
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A 40 nanoTesla (nT) magnetic anomaly identified in an aeromagnetic survey over southern Illinois contours as a localized magnetic high on the west flank of a regional magnetic low. This magnetic anomaly is generally coincident with the Omaha Oil Field in northwest Gallatin County, Illinois. It was initially assumed that cultural sources of steel associated with this oil field were the primary source of the magnetic feature; however, similar oil fields overflown by the survey do not exhibit magnetic anomalies in the data set. The Luther Rister et ux ♯1 well, drilled near the apex of the Omaha structural dome, encountered two zones of ultramafic intrusive rock containing 9.0 percent by volume magnetite. These intrusives were identified to be alnöites which are a class of mantle‐derived ultramafic rock that can be associated with the incipient stages of crustal rifting. A ground magnetic survey verified the presence of the anomaly, and provided detailed data for 3-D modeling of the source. Petrophysical evaluations, magnetic susceptibility measurements and thin section modal analysis were made on drill cuttings from the ultramafic intrusives encountered in the Luther Rister ♯1 well. These measurements were made to constrain the 3-D magnetic modeling by the petrophysical characteristics of the source. After removal of the regional magnetic field, the resulting 140 nT residual magnetic anomaly was successfully modeled using two ultramafic sills with an igneous feeder plug. The two igneous sills adequately account for the structural closure exhibited in the Omaha Oil Field and raise the interesting possibility of other hydrocarbon trapping structures generated by intrusives emplaced into the sedimentary section.
Ultramafic rock
Magnetic survey
Petrophysics
Sill
Aeromagnetic survey
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A land magnetic survey was carried out along regional profile, which is located at the north part of the Iraqi western desert. It starts from al –Qaam City (at north) toward Rutba City (at south) with a total length of 238km. The survey was carried out along the paved road between the two cities, About 113 measuring points were done with inter-station distance of 2 km (for 198 km) and 2 to 5km (for 40km). Two proton magnetometers were used in this survey. One of them is used for base station monitoring, which was fixed as of Salah Aldin field (Akkas). Its readings were used for diurnal corrections. All magnetic measurements were corrected for normal and topographic corrections. The readings were reduced to a certain base level. The resulted magnetic anomalies show a good correlation with those of Arial - magnetic survey anomalies conducted by (C.G.G, 1974). This is true for those anomalies with wavelength more than 50km. While the land magnetic survey has shown more small anomalies which may reflect near surface sources. In addition, there is a considerable difference between the magnetic intensity values of both surveys. The downward continuation method was used in this study for detecting the depth of magnetic anomaly source. But before applying this method the total magnetic field was converted to its vertical component using computer program packages. The 2.5 mathematical modeling techniques were used for interpreting magnetic anomaly. Several models were suggested according to the geological and geophysical surface and subsurface data. These models clearly suggest that the tectonic of the studied area may be completely affected by deep faults that could reach the basements or even cut it. These faults resulted in tectonic blocks with relative movements that could happen through the geological time, and they may be responsible for the tectonic features of the western desert. These faults could also responsible for the lateral and vertical variations that are noticed in subsurface rocks of the studied area. The subsurface lateral susceptibility variation between the different blocks could result from the variation in physical parameter of the rocks (like porosity, fracture density…) and there is a possibility that rocks beneath 18km (lower crust) still possess some magnetic properties.
Magnetic survey
Anomaly (physics)
Field survey
Land area
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