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Applying Source Parameter Imaging (SPI) to Aeromagnetic Data to Estimate Depth to Magnetic Sources in the Mamfe Sedimentary Basin

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International Journal of Geosciences 2024年第1期15卷 1-11页

作者： eric N. ndikum Charles T. Tabod Department of Physics HTTC Bambili The University of Bamenda Bamenda Cameroon Department of Fundamental Sciences Higher Technical Teacher Training College (HTTTC) Bamenda Cameroon Department of Physics University of Yaoundé 1 Yaoundé Cameroon Department of Physics Faculty of Science The University of Bamenda Bamenda Cameroon

Aeromagnetic data over the Mamfe Basin have been processed. A regional magnetic gridded dataset was obtained from the Total Magnetic Intensity (TMI) data grid using a 3 × 3 convolution (Hanning) filter to remove regional trends. Major similarities in magnetic field orientation and intensities were observed at identical locations on both the regional and TMI data grids. From the regional and TMI gridded datasets, the residual dataset was generated which represents the very shallow geological features of the basin. Processing this residual data grid using the Source Parameter Imaging (SPI) for magnetic depth suggests that the estimated depths to magnetic sources in the basin range from about 271 m to 3552 m. The highest depths are located in two main locations somewhere around the central portion of the study area which correspond to the area with positive magnetic susceptibilities, as well as the areas extending outwards across the eastern boundary of the study area. Shallow magnetic depths are prominent towards the NW portion of the basin and also correspond to areas of negative magnetic susceptibilities. The basin generally exhibits a variation in depth of magnetic sources with high, average and shallow depths. The presence of intrusive igneous rocks was also observed in this basin. This characteristic is a pointer to the existence of geologic resources of interest for exploration in the basin.

关键词： Mamfe Basin Aeromagnetic Data Source Parameter Imaging (SPI) Depth to Magnetic Sources

Applying Source Parameter Imaging (SPI) to Aeromagnetic Data to Estimate Depth to Magnetic Sources in the Mamfe Sedimentary Basin

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Characterization of Pan-African Aquifer Layers by the Least Squares Inversion Method Applied on Geoelectric Data

International Journal of Geosciences（地球科学国际期刊） 2024年第1期

作者： eric N.ndikum Charles T.Tabod

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International Journal of Geosciences 2019年第10期10卷 845-859页

作者： Kana T. Idriss Serge H. Pokam Kengni ndikum eric ndoh Blaise P. Gounou Pokam Charles T. Tabod Department of Physics Faculty of Science University of Yaounde I Yaounde Cameroon Department of Physics Faculty of Science University of Bamenda Bamenda Cameroon Department of Physics HTTC Bambili University of Bamenda Bamenda Cameroon.

Geoelectric data obtained from forty (40) vertical electrical soundings collected with a Schlumberger device in the Adamawa plateau region, also known as the Cameroon water tower, have been treated by the least-squares inversion method. In order to study the nature and thickness of the aquifer and the necessary geoelectric parameters, quantitative and qualitative interpretations of the data were made. The results obtained showed that: about four to five geoelectric layers have been delimited in the study area with a dominance of the KH curve, which can be used as a reference for future studies. The first two layers constitute an association of clay and laterite with resistivity values ranging from 58 to 9122 Ω·m and whose thickness is between 0.6 and 13.4 m. The third layer is a potentially aquiferous laterite composed of clay, laterite and especially clay sand and cracked/good granite, with a dominance of sandy alteration whose resistivity values are between 81 and 960 Ω·m and its thickness between 12.2 and 26.8 m. The fourth and fifth layers are made up of cracked/good granite with a resistivity ranging from 12-10705 Ω·m with an average value of 1817 Ω·m. This study also shows that the North-East, South-West and South sectors could be the groundwater convergence zones and that the average depth of the basement aquifer roof is about 28.3 m. The geoelectric sections of certain demarcated vertical electrical sounding stations are consistent with the geologic description of the area.

关键词： Adamawa Plateau Region Vertical Electrical Sounding Geoelectric Sections Aquifer Groundwater

Regional Intrusive Signature from the Cameroon Coastal Basins to Bioko Island in Equatorial Guinea (Gulf of Guinea) Using Gravity Studies

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Journal of Geoscience and Environment Protection 2023年第1期11卷 1-14页

The Gulf of Guinea constitutes an area of great petroleum potential yet with very limited geophysical research information. Consequently in this study, a Bouguer anomaly map has been computed from gravity data covering regions stretching from the Cameroon coastal basins to Bioko island (formerly Fernando Po) which is part of Equatorial Guinea. The data were further processed for Source Edge Detection (SED), Euler 3D deconvolution, 3D surface oriented models and 3D voxel solutions. The results confirmed the presence of previously identified intrusive bodies around the Douala and Kribi/Campo sedimentary sub-basins and went ahead to suggest a probable continuity between these two. A possible extension of this body offshore the Gulf of Guinea right up to Bioko island with very striking similarities was also highlighted and it shows characteristic variations in the depth to the surface of the body at different locations.

关键词： Intrusive Body 3D Surface-Oriented Model Gulf of Guinea

Frequency Time Analysis (FTAN) and Moment Tensor Inversion Solutions from Short Period Surface Waves in Cameroon (Central Africa)

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Open Journal of Geology 2014年第2期4卷 33-43页

作者： eric N. ndikum Charles T. Tabod Alain-Pierre K. Tokam Department of Physics University of Yaounde 1 Yaounde Cameroon

Short period surface waves generated by a local earthquake recorded by broadband seismometers at distances of about 186 to 778 km from the earthquake’s epicenter located in Cameroon (Central Africa) were processed for group velocity maps and dispersion waveforms using the frequency time analysis (FTAN) method. The resulting group velocity fundamental modes of the extracted Rayleigh and Love waves were used for a joint amplitude spectral and P polarity inversion using moment tensor inversion. The corresponding group velocity dispersion curves, the residual as a function of depth, the amplitude spectra and the moment tensor solutions of the regions from the epicenter to the different stations up to a depth of about 10 km were obtained.

关键词： Frequency Time Analysis (FTAN) Surface Waves Group Velocity Dispersion Curves Moment Tensor Inversion

Fault-Plane Solution of the Earthquake of 19 March 2005 in Monatele (Cameroon)

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Open Journal of Geology 2014年第6期4卷 289-293页

作者： eric N. ndikum Charles T. Tabod Alain-Pierre K. Tokam Bernard Z. Essimbi Department of Physics University of Yaoundé 1 Yaoundé Cameroon

An earthquake of magnitude Ml = 3.04 was detected on the 19 of March 2005 at 11:49:18.31 (local time) by seven broadband seismometers located around Cameroon (Central Africa). Its epicenter has been relocated and found to be in Monatele (Cameroon) with latitude 4°26.34' and longitude 10°59.62'. The fault-plane solution calculated using double couple fault-plane solutions based on P-wave polarity readings, also taking into consideration the dextral nature of the Sanaga Fault (SF) underlying this region of the epicenter, is a strike-slip fault with a normal faulting component. The beach ball representation of this fault-plane solution has strike, dip and rake values of 289, 70, -169 for the principal fault plane and 195, 80, -20 for the auxiliary fault plane.

关键词： Earthquake Monatele Epicenter Fault Plane Solution Strike-Slip Fault Normal Faulting Component

Gravity Model for an Anomalous Body Located in the NW Portion of the Douala Sedimentary Sub-Basin, Cameroon (Central Africa)

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Open Journal of Geology 2014年第10期4卷 524-541页

作者： eric N. ndikum Charles T. Tabod Bernard Z. Essimbi Fidèle Koumetio Noutchogwe C. Tatchum Department of Physics University of Yaoundé 1 Yaoundé Cameroon Department of Fundamental Sciences Higher Technical Teacher Training College (HTTTC) Bambili The University of Bamenda Bamenda Cameroon Department of Physics Faculty of Science The University of Bamenda Bamenda Cameroon Department of Physics Faculty of Science University of Dschang Dschang Cameroon Department of Physics Higher Teacher Training College (HTTC) Bambili The University of Bamenda Bamenda Cameroon

Gravity studies have been carried out in the Douala sub-basin which is a sedimentary basin located both onshore and offshore on the South coast of Cameroon between latitudes 3°03'N and 4°06'N and longitudes 9°00' and 10°00'E, covering a total surface area of 12,805 km2. On its onshore portion, the Douala sub-basin has a trapezoic shape and covers a total surface area of about 6955 km2 while the offshore part covers an area of about 5850 km2. Gravity data used in this study are constituted of 912 gravity data points located between longitudes 8°10.2' to 10°59.4'E and latitudes 2°30.6' to 4°59.4'N and the study area is located to the NW section of the onshore portion of the Douala sub-basin. This study area is characterised by considerably high positive anomalies attaining peak values of about 104.1 mGals at longitude 9°9.9' and latitude 4°1.1' with contour lines which are mostly oriented in the NNE direction. Residual anomalies were extracted by upward continuation of the Bouguer anomaly field at an optimum height of 30 km. This residual field and those obtained by the separation of polynomial of order 4 had a very high correlation coefficient factor of 0.979. The multi-scale horizontal derivative of the vertical derivative (MSHDVD) method was applied on the extracted residual anomalies for the delimitation of possible contacts in the source while the amplitude spectrum was used to estimate the depth to the top of the potential field source. The MSHDVD method did not delimite any clear cut contacts in the source but the amplitude spectrum estimated the potential field source at a depth of about 4.8 km. The ideal body theory was used to determine the density contrast along a 65 km NW-SE profile yielding a value of 0.266 g/cm3. 2.5D modelling aimed at bringing out the underlying structural layout of this study area presents a source body which is very probably an intrusive igneous block surrounded by sedimentary formations and having a density of 2.77 g/cm3 at a depth

关键词： Douala Sub-Basin Sedimentary Basin Bouguer Anomaly Residual Field Upward Continuation 2.5D Model Intrusive Igneous Block

Evidence of Some Major Structures Underlying the Douala Sedimentary Sub-Basin: West African Coastal Basin

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Journal of Geoscience and Environment Protection 2017年第7期5卷 161-172页

作者： eric N. ndikum Charles T. Tabod F. Koumetio Noutchogwe C. Tatchum Kenfack J. Victor Department of Physics University of Yaoundé I Yaoundé Cameroon Department of Fundamental Sciences Higher Technical Teacher Training College (HTTTC) Bambili The University of Bamenda Bamenda Cameroon Department of Physics Faculty of Science The University of Bamenda Bamenda Cameroon Department of Physics Faculty of Science University of Dschang Dschang Cameroon Department of Physics HTTC Bambili The University of Bamenda Bamenda Cameroon Department of Earth Science Faculty of Science University of Dschang Dschang Cameroon

Gravity data have been processed in the Douala sedimentary sub-basin in a section consisting of a set of 116 gravity data points located between latitudes 3°03'N and 4°06'N and longitudes 9°00'E and 10°00'E. The established Bouguer anomaly fields and the Residual anomaly fields, extracted by upward continuation at an optimum height of 30 km, were both characterized by considerably high positive anomalies. These anomalies showed many ring-like positive gravity anomaly contour lines in the study region. Gravity gradients were analysed using the multi-scale horizontal derivative of the vertical derivative (MSHDVD) method, and this excluded the existence of fault lines across this region. Amplitude spectrum was used to estimate the potential field source at a depth of about 4.8 km. The ideal body theory capable of handling sparse data contaminated with noise was applied along a 50.2 km WWS-EEN profile to determine a density contrast of 0.266 g/cm3. Using these results as constraints, 2.5 D modelling carried out along this profile presented two major blocks with density contrast of 0.266 g/cm3. The first block is probably an intrusive igneous body with a density of about 2.77 g/cm3 , having an average thickness of about 26 km with its top and base lying at depths of about 4.25 km and 30.25 km respectively. The second block is likely a pillar of igneous material, located at a depth of about 10.77 km with a density of about 2.77 g/cm3 whose base goes deep down beyond the crust-mantle boundary. These results support previous findings that there are similarities between the Douala sedimentary sub-basin and the coastal sedimentary basin of Mauritania-Senegal and thus foster the suggestions of a more extensive movement that would have affected the whole of the West African coast.

关键词： Douala Sedimentary Sub-Basin Bouguer Anomaly Residual Field 2.5D Model Igneous Block

Thickness Variations in the Lithospheric Mantle and the Low Velocity Zone of the Adamawa Plateau (Cameroon) from Teleseismic Receiver Functions

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Open Journal of Geology 2018年第6期8卷 529-542页

作者： Serge H. Pokam Kengni Charles T. Tabod eric N. ndikum Alain-Pierre Kamga Tokam Pascal Gounou Pokam Department of Physics Faculty of Science University of Yaounde I Yaounde Cameroon Department of Physics Faculty of Science The University of Bamenda Bamenda Cameroon Department of Physics HTTC Bambili The University of Bamenda Bamenda Cameroon

Teleseismic events recorded by stations located in the Adamawa Plateau have been treated using the inversion method of receiver functions. These six stations are part of a network of 32 large strip seismic stations installed in Cameroon between 2005 and 2007. This method allowed us to investigate the lithospheric mantle in that region. The results obtained from the velocity model have been compared to some existing results in this region. These results show the existence of a thick crust having an average thickness of about 35.2 km and a corresponding S wave velocity of 3.7 km/s. For an average S wave velocity of 4.4 km/s the lithospheric mantle appears to be thin in nature and has a thickness that varies from 39 km and 49.6 km. Beyond the lower lithospheric mantle, there exists a low velocity zone, whose thickness varies between 20 km and 43.9 km. The variation of the low velocity zone leads to variation of the lower boundary of the lithospheric mantle boundary at the depths ranging from 73.8 km and 85 km.

关键词： Low Velocity Zone Receiver Function Teleseismic Lithospheric Mantle Adamawa Plateau