Collection and Processing of Gravity Data In Nigeria.

Olajiga, B. O (1972)

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Thesis

The main of this dissertation is to predict mean anomalies for 10 x 10 blocks within Nigeria. It is not t o discover new techniques or mathematical models for the computation and prediction of gravity values: neither is it to examine the accuracy of the existing prediction methods. Mean anomalies were estimated from a gravity map for the 10 x 10 blocks having gravity measurements in Nigeria. The estimated values were then used to predict mean anomalies for the empty 10 x 10 blocks. A number of known point anomalies were also used to predict values for the unknown blocks, and a comparison made between the result s of the two predictions. The free air anomaly correlation with elevation was then assumed to exist within the small blocks throughout the country, and consequently a Least Squares Fit carried out for the surveyed areas using the estimated mean anomalies; the mean anomalies for the empty 10 x 10 blocks were again predicted from the resulting straight line.' The value 211kP = 0.03242, for the height, H, in feet, was used in the computation of the free air anomalies fro the Bouguer anomalies. The correlation coefficient for the pairs of the mean gravity values and their corresponding mean elevations was found to be + 0.82. From this, and the correlation between the free air anomaly map derived from the results obtained in this dissertation, and the topographic al map of the country, it was found that there is, to a great extent, a direct correlation between the block mean anomalies and the block mean elevations within the country. And from the least squares fit, it was found that the mean free air anomalies, gF, can be expressed as: gF = - 9.0985 + 0.0172H, H in feet: or gF = - 9.0985 + 0.0053 H in metres.

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