Theory and Application of Full Tensor Gravity Gradiometry for Basement Structure in the Bida Basin

This study develops theoretical extensions to full tensor gravity gradiometry interpretation and applies them to basement structure characterisation in the Bida Basin, North Central Nigeria. Full tensor gravity gradiometry measures all five independent components of the gravity gradient tensor simultaneously, providing substantially more structural information than conventional scalar Bouguer gravity measurements. The Bida Basin is a continental rift basin with significant sediment fill and potential for undiscovered hydrocarbon and evaporite mineral deposits, but its basement configuration and structural evolution are poorly constrained. This study acquires a ground-based tensor gravity gradiometry dataset using a prototype AGT system along 18 profiles totalling 220 kilometres in Bida, Agaie, and Lapai local government areas of Niger State, constituting the first such dataset acquired in Nigeria. Theoretical developments include a novel noise suppression algorithm tailored to the non-stationary noise characteristics of the AGT instrument in tropical terrain, an equivalent source estimation framework for tensor component interpolation, and a minimum entropy joint structural inversion approach for depth estimation from tensor data. Findings demonstrate that the tensor components Tzz and Txz together resolve basement fault geometry 38 percent more accurately than Tzz alone, reducing depth estimation uncertainty from 12 percent to 7 percent in forward modelling validation tests. The Bida Basin basement geometry derived from tensor inversion shows a horst-graben structure with maximum sediment thickness of 3.8 kilometres, significantly deeper than previous gravity-based estimates of 2.5 kilometres. A northwest-trending basement high is newly identified with implications for trap formation. The study contributes three original methodological advances to tensor gradiometry interpretation.

Keywords: full tensor gravity gradiometry, Bida Basin, basement structure, theoretical methods, tensor inversion.