A seismic refraction study of the crustal structure associated with the Adamawa Plateau and Garoua Rift, Cameroon, West Africa

Summary Recordings of quarry blasts along a 300 km profile across the Adamawa Plateau at the eastern end of the Cameroon Volcanic Line permitted the determination of the crustal structure of the region. To the north of the Plateau in the area of the Garoua Rift, an eastern arm of Benue Trough the crust is about 23 km thick and is underlain by upper mantle with a P-wave velocity of 7.8 kms-1. The southern part of the Plateau by comparison is associated with a more normal crustal thickness of about 33 km and underlain by upper mantle with a velocity of 8.0 kms-1. Between these two areas the seismological experiment was not able to delineate how the crust changes. However, if the topography and gravity field reflect crustal thickness then there is a rapid change in crustal thickness at the northern edge of the Adamawa Plateau. The study thus provides the first seismic evidence for major crustal thinning beneath the Garoua arm of the West African Rift System as well as providing evidence for an alternative model for the formation of the Cameroon Volcanic Line.