A Qualitative Interpretation of Residual Magnetic Anomaly using Ground Magnetic Data

This research aims at analyzing and interpreting residual magnetic anomalies for the determination of subsurface geology of the area under study. We employed the use of ground magnetic survey method for the subsurface delineation of a location within Federal University of Agriculture, Abeokuta, an area of 6600 Π2 with geographical coordinates of latitude 7.23707°N to 7.23777°N and longitude 3.43693°E to 3.43858°E. The magnetic data was collected using a G816 proton precision magnetometer. A total of 21 profiles were established along traverses. From these profiles it was seen that the intensities and characteristics nature of the magnetic anomalies, are indicative of the different rocks producing them. Analysis of residual anomaly graph reveals the existence of some structural features such as fault, fractures and contact between rocks and any other subsurface structure of the study area. When the anomaly is higher than the IGRF value, there is said to be a near surface magnetic material (igneous intrusion), but when the anomaly is below the IGRF value, then there is said to be a non-magnetic material such as fault, fracture, etc (sedimentary basin).Keywords: Proton precession magnetometer; residual; anomaly; qualitative; IGR

Separation of Regional-Residual Anomaly Using Least Square Polynomial Fitting Method

This paper presents quantitative application of Least-Square Polynomial fitting method in regional-residual separation. The study area covered geographical coordinate between latitude 8˚06΄70˝N and 8˚06΄98.7’’north and longitude 4˚14΄28.2˝E and 4˚14΄56.9˝ east of the Aeromagnetic maps of the region. The data were obtained by digitizing the maps of the above areas, picking the Total magnetic values along the profile line, processed and analyzed. The result of the residual separation revealed that the area is underlain by a NE-SW regional trend, characterized by basement complex with a weak amplitude of approximately – 85.73l nT. The regional magnetic anomaly map shows that the southern part of the map is suspected to be sedimentary basin, which is W-E trending, an indication of smoother magnetic field and it masked off the effects of the stronger magnetic basement. The basement complex underlies between the north and south of the study area comprises of broader area of outcrops.Keywords: Aeromagnetic map, Regional and Residual fields, basement complex, Polynomial fittin