Upper Crustal Structure of Cameroon (West Africa) from Ambient Noise Love Wave Tomography

We perform Love wave tomography in Cameroon, West Africa by applying the ambient noise method to broadband data recorded at 32 stations from a temporary digital seismic network.

Cross-correlations of transverse-component ambient noise data are computed in one-hour segments and stacked over 12 months from January to December 2006. Then Love wave group and phase dispersion curves from 5 to 30 s were measured using the frequency time analysis method. Tomographic inversion were performed on a 0.5° × 0.5° grid for 2-D group and phase velocity maps and jointly inverted for a unified isotropic 3-D shear wave velocity (Sh) model constrained reliably to a depth of 20 km.

The velocity model shows variations in wave speed which reflects lateral heterogeneities that correlate well with surface geology in the study area. A broad fast shear wave velocity zone in southern Cameroon coincides with the Congo Craton and a conspicuous slow shear wave velocity is revealed along the Cameroon Volcanic Line (CVL), the northern boundary with Nigeria up to Garoua Rift.

Our study concluded that the upper crustal structure exhibit a fair amount of homogeneity within the same region and heterogeneity between different regions suggesting little modification of the entire upper crust.