A seismological network was operated at the junction of the aseismic Walvis Ridge with the northwestern Namibian coast. We mapped crustal thickness and bulk Vp/Vs ratio by the H-k analysis of receiver functions. In the Damara Belt, the crustal thickness is ∼35km with a Vp/Vs ratio of <1.75. The crust is ∼30km thick at the coast in the Kaoko Belt. Strong variations in crustal thickness and Vp/Vs ratios are found at the landfall of the Walvis Ridge. Here and at ∼150km northeast of the coast, the crustal thickness increases dramatically reaching 44km and the Vp/Vs ratios are extremely high (∼1.89). These anomalies are interpreted as magmatic underplating produced by the mantle plume during the breakup of Gondwana. The area affected by the plume is smaller than 300km in diameter, possibly ruling out the existence of a large plume head under the continent during the breakup. Key Points Thick crust, high Vp/Vs ratios is found at the landfall of the Walvis Ridge Evidence for magmatic underplating beneath the African continental crust The extension of the plume area of influence is less than 300km in diameter