Implications of horsts and grabens on the development of canyons and seismicity on the west africa coast

Subsurface basement topography in the Nigerian portion of the Benin Basin has been studied using borehole data of wells drilled to the basement and one strike line of seismic section. Two areas of a sharp drop in topography with a horst in between were observed in the study area. These features were projected to a seismic section in the offshore area of the Benin basin. The result depicts the structural features as horst and grabens coinciding with the Avon platform bounded on the right side by Ise graben, and the Orimedu graben to the left. The observed relationship of the grabens with the present day location of Avon Canyon on the seismic section also suggests an active subsidence along fractured zones. The subsidence, which probably is occurring along similar fracture zones in the Gulf of Guinea, could be responsible for the occasionally reported seismicity on the margin of West Africa. A detailed seismographic study of the fracture zones is recommended.