A Gravity And Magnetic Analysis Of The Liberia Continental Margin And The Liberia Basin

Understanding our environment and the subsurface has been the quest of man since creation. Geophysicists have device means and techniques to evaluate, unearth and model the contents of the subsurface with a view of mastering and dominating nature. Exploration geophysicists are concern with searching, mapping and exploring the subsurface. Hence, this thesis presents a geophysical investigation of the Liberia continental shelf and margin using potential field data.Gravity and magnetic analysis provide an opportunity to deduce and understand to a large extent the stratigraphy, structure and shape of the substructure. The Liberia continental shelf is underexplored with little or no research on going. A qualitative and quantitative interpretation of the coastal region, the continental shelf and the Liberia basin, unearthing its substructure via wavelets analysis and other standard methods is carried out.Gravity and magnetic maps supported by bathymetry were used for visual interpretation of the geological structure of the shield and margin. Details were enhanced using various derivatives of the field and a depth to basement map produced using parker's method. Inverse model topography of the moho is obtained via wavelet multiscale analysis. I also show that the Liberia Basin lies mostly in deep waters and its structure reveals that it is shallower at its northwest end and deeper at its southeast. Several faults and lineament are inferred along the margin and depths of thick sediments determined. A theoretical model of a section of the basin was constructed based on available data.I applied the empirical Mode decomposition (EMD), an important kernel of the Hilbert-Huang transform to potential field data. The EMD is a new data analysis method suitable to process non-stationary and nonlinear data. Its power to filter and decompose data has earned it a high reputation in signal processing. Its decomposition results in what is called "Residual", which is similar to the regional anomaly of a potential field data. This residual does not require any preset parameters unlike contemporary field separation methods. The method is applied to a magnetic data from the Jinshandian mine in Hubei, China enabling us to construct a 2.5D inverse model inferring the existence of deep ore deposits. A two dimensional EMD based on ensemble EMD is applied to magnetic and gravity data of the Liberia shelf and margin to determine the structure and basement orientation of the broadest section of the basin. The results obtained are compared to those of wavelet decomposition and found to be quite satisfactory.The results presented in this thesis may have some shortcomings based on the quality of the data and the inavialability of seismic and well log data. However, it is an earnest effort to expose the area to a detail investigation.