Upward Continuation and Reduction to Equator Filters on Aeromagnetic Data of Nkalagu and Abakaliki Regions of Lower Benue Trough, Southeastern Nigeria

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Upward Continuation and Reduction to Equator Filters on Aeromagnetic Data of Nkalagu and Abakaliki Regions of Lower Benue Trough, Southeastern Nigeria

Nnaemeka, Ejike Kingsley; Egwuonwu*, Gabriel Ndubuisi; Onyekwelu, Chiagoziem Chukwuma
Department of Physics and Industrial Physics, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria
*Corresponding Author’s
DOI: https://doi.org/10.51244/IJRSI.2023.10405
Received: 20 April 2023; Accepted: 28 April 2023; Published: 04 June 2023

Abstract: This paper adopts two magnetic filtration techniques to enhance the Aeromagnetic maps of Nkalagu and Abakaliki regions of lower Benue trough, Southeastern Nigeria. This aim is to enhance the effectiveness of the map in characterizing the study area. Upward continuation (UPC) and reduction to magnetic equator (RTE) filters were applied to sufficiently improve the interpretation of the aeromagnetic data of the area in terms of recognition and understanding depth continuation and discrimination between shallow and deeper magnetic sources within the study area. The total magnetic intensity and reduction to the equator showed variations in anomalies. The variations were invariably related to magnetic susceptibility, depth, degree of strike, lithology or basement complex rocks harboring varying amounts of magnetic minerals.

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Keywords: Aeromagnetic data, Upward Continuation reduction to the equator and anomalies

I. Introduction

Magnetic survey is one of the ancient geophysical methods employed for the investigation of hydrocarbon and mineral deposits. The method probes the internal structures of the earth based on magnetic field variations that occur due to magnetic properties of the underlying rocks. [1] opined that magnetic method tends to probe the geology of an area of interest due to its earths magnetic field differences. The differences being the responses’ results of magnetic features of the rocks in subsurface. This method is very effective in the determination of the probable depth to basement beneath sedimentary rocks [2]. The upward continuation process is a technique that projects data higher above the original height the data was taken. Its effect is that short wavelength features are smoothed out because one is moving away from the anomaly [3]. The upward continuation method is also introduced in oil exploration geophysics to estimate the values of a magnetic or gravitational field by using the measurements at low elevation and extrapolating upwardly; thereby assuming continuity. In terms of magnetic interpretation, upward continuation attenuates high wave number anomalies concomitant with the shallow magnetic sources, thus by allowing comfortable interpretation or explanation of deeper magnetic sources. It is also adopted to separate a regional magnetic anomaly resulting from deep-seated sources from the observed magnetic sources whereas the reduction to magnetic equator is employed in low magnetic latitudes; That is, areas with geomagnetic inclination less than 15˚ to center the peaks of low magnetic anomalies over their sources or exact positions. This enhancement over extreme or outermost magnetic anomalies is over their sources, thereby enabling magnetic interpretation easier. In reduction to the equator, it is not with little rigors when it is required to correlate the observed abnormal maxima and the positions of sources since magnetic signature of magnetized bodies at low latitudes always have two extreme values because of their bipolar nature [3]. [4] also proposed that the magnetic data can be reduced to the equator (RTE) such that the magnetic bodies will appear horizontal at the equator. Therefore, the aim of this study is to employ two magnetic enhancement procedures to the reduction to equator and in upward continuation at various levels on the aeromagnetic data of Nkalagu and Abakaliki regions. It is expected that from selected regions of both in the Lower Benue troughs, it would be observed that the picture of the differences between the shallow and deeper magnetic sources would be unvailed. Thereafter, variations would be noticed from the aeromagnetic data which ones are evident to the change in magnetic susceptibility of near surface rocks.