GRAVITY METER CALIBRATION RANGES IN NIGERIA

Series of precise gravity measurements were made with three La Coste and Romberg model G gravitY meters throughout Nigeria during the establishment of a reference gravity network for the country. The Processed data led to the establishment of a standard gravimeter calibration line in Nigeria. The line designated as the Central Calibration Line (CCL) and situated in the northern part of Nigeria, covers the longest gravity range observed in the country. Its extreme absolute gravity values are 977844.608 mGal at Jos and 978221.324 mGal at Illela which yield a maximum interval gravity value of 376.716 mGal. The absolute gravity values along the calibration line are referred to the IGSN 71 daturn. Comparing the absolute gravity values for the IGSN 71 sites situated in the West African sub-region with those obtained in this study, it is obvious that the gravity values within most West African countries lie within the range of the calibration line. The accuracy of the interval gravity values within the calibration line is, on die average, 15 muGal with maximum and minimum values of 18 muGal and 9 muGal respectively. Thus the calibration line should meet the calibration requirements of precision gravimetric studies in Nigeria and in other neighbouring countries in West Africa.