Contribution of topographic and penetrometric measurements to a site characterization, case of the kekem landslide, national road n°5 (western cameroon)

Atopographical survey and a dynamic cone penetrometer testing (DCPT) were conducted over the Kekemlandslide area.The aim of the work was to unveil new topographic features of the site, and with the penetrometer soundings predict the depth of the potential rupture surface beneath the damaged area. The analysis of penetrometer data has led to the supposition that the fractured surface interface connecting the basement and sediments has a depth of between 2.00m and 12.20 m. The topographic data was used to determine the average slope percentage over the broken area. The slope percentage gives 33.66% from a point taken over the tearing niche and a point along the road.2Dcontoursmapdrawn with the Surfer software, over an area of 35 hectares has enabled the observation of a step gradient oriented NNE-SSW. Considering the steepness of the slope and the thickness of the sediments, the site remains dangerous for the populations especially during the rainy season

Identifikacija tektonskih lineamenata korištenjem aeromagnetskih podataka za područje jugoistočnog Kameruna

The subsurface structures in a part of the Congo Craton in south-eastern Cameroon, between the latitudes 2° to 3° N and longitudes 13° to 15° E, has been estimated by the interpretation of aeromagnetic data. Magnetic survey is used to delineate magnetic lineaments, analyze its relationship to the tectonic fabric and to estimate the depth of perturbing body source, probably granitic intrusion along one profile selected on the total magnetic intensity reduced to the equator (TMI–RTE) map by means of forward modelling and inversion constrained by surface geology and results from Euler deconvolution analysis method. Determination of the magnitude maxima of the first vertical derivative (FVD) of the residual field reduce to the equator allowed a map to be produced showing various aeromagnetic lineaments interpreted as the fault system of the studied area. Particularly, looking at the center of the structural map, we find that these structures are associated to long-wavelength anomalies, suggesting that its should be connected with large-scale structural deformation. The pseudo-gravity map shows the extension of the tillitic formations on the geological map. Our results confirms the morphological difference and the tectonical subdivision into two tectonic sectors corresponding to the Congo Craton in the south, Pan-African in the north and also helped identify the tectonic boundary separating them at depth.Pomoću interpretacije aeromagnetskih podataka procijenjene su strukture ispodpovršine tla u dijelu Kongoanskog kratona u jugoistočnom Kamerunu, između zemljopisnih širina 2° i 3° N i dužina 13° i 15° E. Magnetski premjer korišten je za prepoznavanje magnetskih lineamenata duž izabranog profila na karti ukupne jakosti magnetskog polja reduciranog na ekvator (TMI-RTE), za analizu njihova odnosa prema tektonskoj građii za procjenu dubine izvora perturbacija, vjerojatno granitnih intruzija. Korišteno je izravno modeliranje te inverzija ograničena površinskom geologijom i rezultatima dobivenim metodom Eulerove dekonvolucije. Određivanje iznosa maksimuma prve vertikalne derivacije (FVD) rezidualnog polja reduciranog na ekvator omogućilo je izradu karte kojapokazuje različite aeromagnetske oblike interpretirane kao sustav rasjeda u razmatranompodručju. Pobliže, gledajući strukturne karte nalazimo da su ove strukture povezane sdugoperiodičnim anomalijama, sugerirajući da one moraju biti povezane sa strukturnimdeformacijama na velikoj skali. Naši rezultati potvrđuju morfološke razlike i tektonsku potpodjelu u dva tektonska sektora koji se podudaraju s Kongoanskim kratonom na jugu i Pan-afričkim strukturama na sjeveru, te pomažu u identificiranju tektonskih granica koji ih razdvajaju u dubini

A Comparative Geophysical Study of the Sedimentary-Metamorphic Contacts in the Douala and Kribi-Campo Sub-Basins of Cameroon

The magnetotelluric method has been used in this work to compare the nature of the sedimentary-metamorphic contacts of the Douala and Kribi-Campo sub-basins in Cameroon. The results show that the sedimentary-metamorphic contact zones for the two sub-basins, marked by a subsidence of the low resistivity materials on the sedimentary formations and uplift of the high resistivity materials characterized by intrusive bodies of higher values of resistivity on the metamorphic formations, are structurally similar,. However, the very low values of resistivity of rocks in the Douala sub-basin is suggestive of high porosity, permeability and high level of saline ions dissociation leading to high conductivity. These rocks should be of unconsolidated sediments for the sedimentary formation and gneiss for the metamorphic formation. On the contrary, the very high values of resistivity for rocks in the Kribi-Campo sub-basin indicate the absence of free mobile electrons and ions and low porosity, permeability and non-conductivity. The sedimentary formation of this sub-basin should be composed of limestone and conglomerates rocks with some gneissic and unconsolidated granitic materials. The rocks in the metamorphic formation should be completely granitic in nature. The shallow depth of penetration of only 4 km of telluric current in the Douala sub-basin is enough evidence that the tectonic events responsible for the emplacement of this contact zone were limited to the earth crust. On the other hand, in the Kribi-Campo sub-basin the tectonic events should have originated from within the earth mantle as the depth of penetration of telluric current attains 150 km

Evidence for precambrian faulting in the tibati-adamawa region of cameroon using the audiomagnetotelluric method

La falla de Adamawa es una estructura tectónica relacionada con la línea volcánica de Camerún. Se han obtenido datos ATM a lo largo de una superficie de casi 1,600 km2 alrededor de la ciudad de Tibati. El conocimiento geológico del área es escaso; los últimos datos se recopilaron hace 50 años. Este artículo describe las etapas principales, seguidas de la determinación de la firma electromagnética de la falla. Los resultados muestran numerosas zonas anómalas atribuidas a la zona de Cizalla. Todo ello nos permiten inferir la estructura de la resistencia eléctrica y hacen posible tener conocimiento acerca de la falla de Tibali. Estos resultados son preliminares a un estudio de la estructura de esta falla precámbrica. En este estudio se produjeron valores y variaciones importantes de la aparente resistencia. La falla de Tibati se caracteriza por su gran complejidad y estrechez. doi: https://doi.org/10.22201/igeof.00167169p.2011.50.2.13