Gravity Inversion of the Gongola Basin Fault Structures Using the Step Model

Abstract

Gravity anomalies with step-like appearance are often attributed to fault structures. Analysis of gravity anomalies due to such structures is then tantamount to solving the four fault parameters: depth to the surface, sediment thickness, density contrast and the fault dip. In this research, a gravity inversion using the step model was carried out to simultaneously estimate the four parameters of the faulted bed. The model assumes a configuration that the basin is filled with homogeneous sediments. Three characteristic curves were adopted for estimating the fault parameters.Analysis of the residual anomaly profiles of the fault structures showed that the fault structures were independent of the strike length. The estimated depth to the surface and the sediment thickness yielded the basement depth. The basement depth obtained from the gravity profiles showed a maximum basement depth of 1.0 km in the south-western part, and 7.0 km in the north-eastern part of the project area. The estimated basement depth yielded plausible geological model that corroborates with depth obtained using seismic and well information. The computed density contrast was used in the determination of density contrast and rock density maps of the basin. This helped in defining the basin into zones of sedimentary, basement complex and granite pluton.