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Crustal thickness beneath Atlas region from gravity,topographic,sediment and seismic data

Geodesy and Geodynamics 2020年第1期11卷 18-30页

作者： Franck Eitel Kemgang Ghomsi Robert Tenzer sévérin nguiya Animesh Mandal Robert Nouayou Department of Physics The University of YaoundeⅠYaoundeCameroon Department of Land surveying and Geo-Informatics Hong Kong Polytechnic UniversityHong KongChina Faculty of Industrial Engineering University of DoualaDoualaCameroon Department of Earth sciences Indian Institute of TechnologyKanpurIndia

The Atlas region in northwest Africa is characterized by the Quaternary volcanism and elevated topography with past complex tectonic mitigation between the African and European *** of this atypical region has left indubitably imprints in crustal architectonics,mainly regarding the crustal thickness as well as the crustal density *** knowledge of crustal thickness variations is of a significant interest,since it provides a crucial constraint to geodynamic and geophysical modelling of this *** this study,we use gravity,topographic,bathymetric and sediment data together with results of seismic surveys to image the Moho topography beneath the Atlas *** Bouguer gravity anomalies used for a gravimetric Moho recovery are obtained from the free-air gravity anomalies after subtracting the gravitational contributions of topography,bathymetry and *** regional gravimetric Moho inversion constrained on seismic data is carried out by applying a regularized inversion technique based on Gauss-Newton’s formulation of improved Bott’s method,while adopting Earth’s spherical *** numerical result reveals relatively significant Moho depth variations in the Moroccan Atlas,with minima of approximately 24 km along continental margins of the Mediterranean sea and maxima exceeding 51 km beneath the Rif *** Moho depth beneath the West African Craton varies from 32 km in its southern margin to 45 km beneath the Middle *** Tell Atlas is characterized by the shallow Moho depth of approximately 22 km and further deepening to 42 km towards the northern edge of the Aures *** findings indicate a limited tectonic shortening of the High Atlas with the crustal thickness mostly within 36-42 *** discrepancies between the Rif Cordillera and the Atlas Mountains suggest that the hypothesis of isostatic compensation cannot be fully established.

关键词： Atlas Gravity Inversion Moho seismic data

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Choice of suitable regional and residual gravity maps, the case of the south-West Cameroon zone

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Earth and Planetary Physics 2019年第1期3卷 26-32页

作者： Fidèle Koumetio Donatien Njomo Constant Tatchum Noutchogwe Eric Ndoh Ndikum sévérin nguiya Alain-Pierre Kamga Tokam Department of Physics Faculty of Science University of Dschang Department of Physics Faculty of Science University of Yaounde I Department of Physics ENS Bambili University of Bamenda Department of Fundamental sciences H.T.T.T.C.Bambili-Bamenda University of Bamenda Department of Physics Faculty of Genial Engineering University of Douala

The quantitative interpretation of gravity anomalies due to shallow structures needs separation between long wavelength anomalies(regional anomalies) and short wavelength anomalies(residual anomalies).The regional-residual field separation can be carried out using the polynomial *** this case, the so-called regional field of order n is treated as a polynomial of degree *** present study shows that the degree n must vary between a smallest value n_(min) and a maximum value n_(max).This article presents a method to process gravity data that allows determination of n_(min) and n_(max) for a given study *** apply the method to gravity data of the south-West Cameroon *** this chosen study area, we find that regional anomaly maps of orders ranging from 1 to 9 and residual anomaly maps of orders ranging from 1 to 8 can be used for suitable *** analyses show that one may need residual anomaly maps of several orders to perform satisfactory quantitative interpretation of the different intrusive bodies found in a given area.

关键词： gravity regional anomaly residual anomaly upward continuation correlation factors intrusive body

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Refinement of Bouguer anomalies derived from the EGM2008 model,impact on gravimetric signatures in mountainous region:Case of Cameroon volcanic Line,Central Africa

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Earth and Planetary Physics 2020年第6期4卷 639-650页

作者： Paul Gautier Kamto Cyrille Mezoue Adiang severin nguiya Joseph Kamguia Loudi Yap Geodesy Research Laboratory National Institute of Cartography(NIC)YaoundeCameroon Department of Physics Faculty of ScienceUniversity of Yaounde ICameroon Laboratory E3M Faculty of Industrial EngineeringUniversity of DoualaCameroon Department of Physics Faculty of ScienceUniversity of DoualaCameroon

Global geopotential models have not included the very high frequencies of the Earth’s external gravity *** is called omission *** omission error becomes more important in mountainous areas(areas with highly variable topography).The work reported here consists in reducing the omission error in measurements of Bouguer gravity anomalies,by refining the global geopotential model EGM2008 using the spectral enhancement *** method consists in computing the residual terrain effects and then coupling them to the gravimetric signal of the global geopotential *** compute the residual terrain effects,we used the Residual Terrain Model(RTM)*** refine it required a reference surface(ETOPO1)developed up to degree 2190(the maximum degree of the EGM2008 model)and a detailed elevation model(AW3D30).Computation was performed with the TC program of the GRAvsOFT *** topography of the study area was assumed to have a constant density of 2670 kg/*** the inner and outer zones,the respective integration radii of 10 km and 200 km have been *** obtained very important RTM values ranging from−53.59 to 34.79 *** values were added to the gravity anomalies grid of the EGM2008 model to improve accuracy at high *** a part of the Cameroon volcanic Line and its surroundings(mountainous area),we made a comparison between the residual Bouguer anomalies before and after *** report differences ranging from−37.40 to 26.40 *** conclude that the impact of omission error on gravimetric signatures is observed especially in areas with high variable topography,such as on the Cameroon volcanic Line and around the localities of Takamanda,Essu,Dumbo,and *** finding illustrates the great influence that topography has on accurate measurement of these gravity anomalies,and thus why topography must be taken into *** can conclude that in preparing a global geopotential model,a high resolution DTM must be used to decrease

关键词： residual Terrain Model EGM2008 Omission error refined Bouguer anomalies mountainous area

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Delineation of Lineaments in south Cameroon (Central Africa) Using Gravity Data

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Open Journal of Geology 2013年第5期3卷 331-339页

作者： Owona Angue Marie Louise Clotilde Tabod Charles Tabod nguiya séverin Kenfack Jean victor Tokam Kamga Alain Pierre Department of Physics Advanced Teacher Training College The University of Yaounde I Yaounde Cameroon

Gravity method is among the most applied geophysical methods in mineral and oil exploration. It may help to identify fault networks which are of interest for mineral exploration. Potential field data can give valuable information on the location of faults in the basement. These faults may have propagated into the overlying sedimentary rocks and influenced fluid flow and distribution of hydrocarbon traps and mineralization zones. A study was therefore conducted in south Cameroon with the aim of highlighting the different lineaments of the region, which were completely or partially hidden by the sedimentary cover. Different gravity data processing techniques including horizontal gradient coupled with upward continuation and Euler deconvolution were used. The application of these methods has mapped out a number of lineaments depicting gravity density discontinuities whose directions are Ns, NE-sW, EW and NW-sE. The predominant direction for major lineaments is NE-sW. The major lineaments associated to the faults are: the Kribi-Edea faults, Ambam faults, Ebolowa-south of Yaounde faults;Bipindi-Yaounde faults;Pouma-Yaounde fault and the fault system which crosses the east, north, west of Monatele city. Euler solutions indicate depths up to18 km for the roof of the faults. The main results worked out from this study provide with new elements that allow the improvement of the knowledge on the structure of the study area. The structural map obtained shows major tectonic events that are responsible of the structural layout of the study zone. In addition, information related to the dip and depth of the various structures was also obtained. The map of lineaments is a useful tool for the planning of hydrogeological and/or petroleum investigations.

关键词： south Cameroon Bouguer Anomaly Upward Continuation Horizontal Gradient Euler Deconvolution Lineament

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Crustal structure beneath Cameroon from EGM2008

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Geodesy and Geodynamics 2014年第1期5卷 1-10页

作者： Ngatchou Heutchi Evariste Liu Genyou Tabod Charles Tabod Kamguia Joseph nguiya severin Tiedeu Alain KE Xiaoping state Key Laboratory of Geodesy and Earth's Dynamics Institute of Geodesy and GeophysicsChinese Academy of Sciences Department of Physics Faculty of ScienceUniversity of Yaoundé I National Institute of Cartography Industrial Engineering Faculty University of Douala Ecole Nationale supérieure Polytechnique Université de Yaoundé I

We used the Earth Gravitational Model （EGM2008） data sets to analyze the regional gravity anoma- lies and to study the underground structures in Cameroon. We first created a high-resolution Free-Air anomaly database, then corrected the gravity field of the topographic effect by using ETOPO1 DEM with a resolution of 0.01~ to obtain the Bouguer anomaly, then applied a multi-scale wavelet-analysis technique to separate the gravity-field components into different parts of shallow-to-deep origins, and finally used the logarithmic power spectrum technique to obtain detailed images and corresponding source depths as well as certain lateral inho- mogeneity of structure density. The anomalies of shallow origin show successive elongated gravity ＂highs＂ and ＂lows＂ attributable to subsurface Tertiary and lower Cretaceous undulations. Our results are in good agreement with previous investigations.

关键词： Cameroon EGM2008 gravity anomalies wavelet transform power spectrum crustal structure

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