Three different sets of geophysical data are used to investigate the structure of the transition zone between the north-western boundary of the Congo Craton (CC) and the Kribi-Campo sedimentary basin. These are shear wave velocity, gravity and magnetotelluric (MT) data, respectively. The combined use of these data helps to reduce the non-uniqueness of solutions inherent to forward models, leading to a better inference of the structure of the transition zone. The interpretation of shear wave velocity models enhanced the difference in composition of upper crustal layers against the similar composition (densities of ~3.0 g/cm 3 ) of the lower crust, with different thicknesses beneath both tectonic regions. The analysis of gravity maps obtained from the area shows the signature of the main geological units and particularly the north-south gradient correlating with the strike direction of the so-called Kribi-Campo fault (KCF). Using constraints from shear wave velocity models together with surface geology observations, a 2D1/2 gravity model was obtained along a profile crossing the CC margin and the Kribi-Campo sedimentary basin. The new model is consistent with the presence of a thick mafic layer (>10 km) at depth below 18 km beneath both geological units, and also with crustal thicknesses of 28 km and 45 km beneath the basin and CC, respectively. The model also suggests that KCF resulted from the intrusion of magmatic rocks during the continental collision, which were later metamorphosed into granulites. The resulting suture may be interpreted from the model as the thrusting of the Panafrican Mobile Belt rocks onto the CC. Similar conclusions are inferred from the MT model and the signature of the above mentioned presence of granulites is interpreted in this case as low resistive rocks emplaced into high resistive materials. This provides additional support for the gravity model.

The cartography of lineaments across a territory can be optimized using geophysical potential field data. In this study, land gravity and EMAG2 (Earth Magnetic Anomaly Grid) data were simultaneously used to identify and characterize the major lineaments that spread across Cameroon. The data were filtered using a multi-scale approach including horizontal and vertical gradient analyses. The Euler Deconvolution method was later applied to the filtered data to estimate the extension and depth of the identified lineaments. Results show that the main lineaments across Cameroon are laterally extended with a dominant N45°E orientation. Some of these lineaments correlated well with the geographical location of some known major tectonic structures found across the country. The depth of these lineaments varies between 1 and 35 km. Some of the identified faults are still active as their location correlated with the location of some recent earthquakes that occurred in Cameroon. This work, therefore, highlights some hidden tectonic features which knowledge generally precedes exploration for subsurface resources. Graphical Abstract

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Teleseismic events have been selected from a database of earthquakes with three components which were recorded between February 2005 and January 2007 by five seismic stations across the Garoua rift region which constitutes a part of the Cameroon Volcanic Line (CVL). The iterative time deconvolution performed by [1] applied on these teleseismic events, permitted us to obtain P-receiver functions. The latter were subsequently inverted in order to obtain S-wave velocity models with respect to depth which were then associated to the synthetic receiver functions. This made it possible to explain the behavior of the wave and the medium through which they traveled. The main results obtained indicate that: (1) The lithosphere appears to be thin in its crustal part with a mean Moho depth of 28 km and S wave velocity of 3.7 km/s. (2) In its mantle part, the lithosphere is thick in nature having a thickness that varies between 42 km and 67.2 km. The greatest depth is noticed towards the center located around Garoua while the least depth corresponds to a location around Yagoua in the North. The Low velocity zone which makes it possible to determine the depth of the lithosphere was seen to have a thickness which varies between 42 km and 118.8 km. (3) The synthetic receiver functions associated to shear velocity models reveal that, on one hand the wave has really undergone a conversion and multiple conversions such that the existing Ps phase and subsequent reverberations PpPs and PpSs have mean times of 3.7 s, 11 s and 17.6 s respectively. On the other hand, they reveal an attenuation shown by the decrease in the amplitude of the aforementioned phases along a South-North direction in the Garoua rift.