The Use of Magnetic Survey in Engineering Site Characterization

Engineering site investigation using magnetic geophysical survey was carried out in Rufus Giwa Polytechnic, Owo, Ondo State, Southwestern Nigeria, with aim of investigating subsurface geology on the basis of anomalies in the earth’s magnetic field resulting from the magnetic properties of the underlying rocks. The ground magnetic survey was carried along twenty-six traverses with the use of GSM-8 Proton Precision Magnetometer taken at regular station interval of 10 m. After the taking readings along each traverse, the final base station reading and time for that traverse are also recorded and drift, the drift constant and the drift correction were applied to the data collected. The magnetic field intensity over the study area is generally noisy (multiples anomalous zones) of thin magnetic anomalies. The relative magnetic intensity across the study area varies between -16090 and +1741 nT. Although this variation of values is not unusual in the crystalline basement terrain. The magnetic profiles show a low magnetic anomaly which could be associated with joint, fault or weathered materials. Also, pockets of sharp thin negative anomaly suspected to be thin dykes and ‘W-shape’ like magnetic anomaly typical of thick dyke. There are multiple anomalies observed along some profiles which suggest an inhomogeneity within the subsurface materials.