The southern Nigeria gravimeter calibration line

The southern Nigeria Gravimeter Calibration Line (SNGCL) is derived from a Series of precise gravity measurements made with three LaCoste and Romberg model G gravity meters in order to establish a primary gravity network for Nigeria. The SNGCL extends from Benin to Abeokuta. thus covering a total distance of about 507 km. Its extreme absolute gravity values are 978042.409 mGal and 978119.857 mGal at Benin and Abeokuta, respectively, yielding a maximum interval gravity value of 77.448 mGal. The five base stations along the line are fairly uniformly spaced both in terms of their special separations and the interval gravity values between consecutive base stations. The absolute gravity values along the calibration lime are referred to the IGSN 71 datum through a network of gravity stations. The average accuracy of the interval gravity values within the calibration line is ?13 mGal, with worst and best values of 15 mGal and 11 mGal. respectively. Other calibration limes can be deduced from the distribution of the absolute gravity in southern Nigeria, but the SNGCL provides the largest gravity range in the region, with Benin as the focal point from which all limes radiate. It was concluded that periodic measurements along the calibration lime will provide a means of monitoring possible crustal movements within the earth tremor zone of Southern Nigeria.