Moho Depth and Crustal Velocity Structure Beneath Stations RTC and TAM from Teleseismic Receiver-Function Analysis

We apply the P-wave receiver-function technique to invert teleseismic data to investigate the S- wave velocity structure beneath stations RTC and TAM in West Africa. Teleseismic waveform receiver function analysis is a widely used technique for studying crustal structure beneath broadband seismic stations. Our results show that the crust beneath RTC is relatively complex with large velocity fluctuations. In the upper crust, a low velocity layer extends from 8 to 12 km deep. At Tamanrasset crustal structure east and west of the station differ. We find a high-velocity zone between 2 and 8 km to the east that we attribute to a high conductivity unit corresponding to intrusions described in the literature. We find no similar feature west of the station. Our velocity models for RTC and TAM are consistent with their differing tectonic environments. TAM, on a stable craton, displays a fairly homogeneous velocity structure while RTC, on thick sediments in an ocean-continent transition zone, has more heterogeneous structure. This structural difference is reflected as well by the depth to Moho, ~20 km at RTC and nearly 38 km at TAM, although both have gradational velocity increases with depth.