Computation of Ground Magnetic Declination and Horizontal Intensity Maps on the Basis of Measured Vertical Intensity Data in Fupre, Niger Delta

ABSTRACT The aim of this study is to introduce an enhanced technique used for mapping subsurface structures in a sedimentary environments making use of the magnetic data. This involves the computation of magnetic declination and horizontal intensity maps from the acquisition of the vertical component of the magnetic field at Premium Steel Mines Company located at DSC Aladja in Delta State. Two (2) dip lines and two (2) strike lines were established in the area. The measured vertical magnetic field was corrected using appropriate corrections method. Contour maps of measured vertical field and its corrected values were produced and the corrected vertical field showed better image clarity than the measured vertical field with zones of high magnetic intensity localized at the central portion of the area. This was an enhancement over the dataset and reflects the proper geology of the study area as the correction helped to sharpen the image and its interpretation. The declination attribute map shows high and low values, with positive values observed at the central portion of the map where the magnetic north is east of the true north, while the horizontal magnetic field map which is the component of the total field strength of earth's magnetic field in the horizontal direction in the magnetic meridian shows the intensity of the total field variation in the horizontal direction of the earth in the study area. The pattern of magnetic variation observed was consistent with that observed in the corrected vertical field with the central portion of the map showing a steep slope (closely spaced contour) while the North Eastern area show an anticlinal structure which decreased gentle outwardly. Although the susceptibilities are low in the area because the magnetism experienced in the area is either diamagnetic or paramagnetic, the result indicates that enhanced visibility of subsurface magnetic materials can be obtained in sedimentary environment by computing attributes of the measured field since the underlying geologic materials are weak and show only feeble changes in magnetic susceptibility.