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Integrated marine gravity field in the Brazilian coast from altimeter-derived sea surface gradient and shipborne gravity

PAOLO, F. S.; MOLINA, E. C.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.33%
Sea surface gradients derived from the Geosat and ERS-1 satellite altimetry geodetic missions were integrated with marine gravity data from the National Geophysical Data Center and Brazilian national surveys. Using the least squares collocation method, models of free-air gravity anomaly and geoid height were calculated for the coast of Brazil with a resolution of 2` x 2`. The integration of satellite and shipborne data showed better statistical results in regions near the coast than using satellite data only, suggesting an improvement when compared to the state-of-the-art global gravity models. Furthermore, these results were obtained with considerably less input information than was used by those reference models. The least squares collocation presented a very low content of high-frequency noise in the predicted gravity anomalies. This may be considered essential to improve the high resolution representation of the gravity field in regions of ocean-continent transition. (C) 2010 Elsevier Ltd. All rights reserved.; National Council for Scientific and Technological Development (CNPq)[132488/2007-8]

Investigation of the Goias Alkaline Province, Central Brazil: Application of gravity and magnetic methods

Dutra, Alanna Costa; Marangoni, Yara Regina; Junqueira-Brod, Tereza C.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD Publicador: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.29%
We investigate the strong magnetic and gravity anomalies of the Goias Alkaline Province (GAP), a region of Late Cretaceous alkaline magmatism along the northern border of the Parana Basin, Brazil. The alkaline complexes (eight of which are present in outcrops, two others inferred from magnetic signals) are characterized by a series of small intrusions forming almost circular magnetic and gravimetric anomalies varying from -4000 to +6000 nT and from -10 to +40 mGal, respectively. We used the Aneuler method and Analytical Signal Amplitude to obtain depth and geometry for mapped sources from the magnetic anomaly data. These results were used as the reference models in the 3D gravity inversion. The 3D inversion results show that the alkaline intrusions have depths of 10-12 km. The intrusions in the northern GAP follow two alignments and have different sizes. In the anomaly magnetic map, dominant guidelines correlate strongly with the extensional regimes that correlate with the rise of alkaline magmatism. The emplacement of these intrusions marks mechanical discontinuities and zones of weakness in the upper crust. According to the 3D inversion results, those intrusions are located within the upper crust (from the surface to 18 km depth) and have spheres as the preferable geometry. Such spherical shapes are more consistent with magmatic chambers instead of plug intrusions. The Registro do Araguaia anomaly (similar to 15 by 25 km) has a particular magnetic signature that indicates that the top is deeper than 1500 m. North of this circular anomaly are lineaments with structural indices indicating contacts on their edges and dikes/sills in the interiors. Results of 3D inversion of magnetic and gravity data suggest that the Registro do Araguaia is the largest body in the area...

"Estudo de anomalias gravimétricas e aeromagnéticas das alcalinas morro de engenho e A2, sudoeste de Goiás"; Study of Gravity and Aeromagnetic Anomalies of Morro do Engenho and A2 Alkalines, SW Goias.

Dutra, Alanna Costa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/04/2006 PT
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A Província Alcalina Rio Verde - Iporá, na borda norte da Bacia do Paraná é caracterizada pela presença de intrusões alcalinas com forte assinatura aeromagnética e gravimétrica, apresentando-se como anomalias quase circulares. O trabalho refinou o levantamento gravimétrico na região sudoeste de Goiás, incluindo um levantamento de detalhe sobre as intrusões de Morro do Engenho (ME) e uma intrusão a poucos quilômetros a NE de Morro de Engenho (A2), com informações gravimétricas e aeromagnéticas, e sobre a anomalia gravimétrica próxima à cidade de Britânia, sem informação de anomalia aeromagnética. As anomalias gravimétricas variam de 15 a 30 mGal com relação ao campo gravimétrico regional, enquanto que as anomalias aeromagnéticas são da ordem de ±3000nT. Foram feitas também medidas das propriedades petrofísicas de amostras da área. Os resultados da inversão 2D e 3D dos dados gravimétricos e 3D dos dados magnéticos indicam que os corpos alongam-se dentro da crosta superior até a profundidade máxima de 10 km e diâmetro da ordem de 8 km, com geometria aproximadamente cilíndrica. Os dados gravimétricos e aeromagnéticos de ME foram tratados de forma conjunta por modelamento direto (2,5D) onde foi incluída a magnetização remanescente...

O uso dos dados da missão GOCE para a caracterização e a investigação das implicações na estrutura de densidade das Bacias Sedimentares do Amazonas e Solimões, Brasil; The use of the GOCE mission data for characterizations and implications on the density structure of the Sedimentary Basins of Amazon and Solimões, Brazil

Bomfim, Everton Pereira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/12/2012 PT
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36.41%
A maneira mais direta de detectar as anomalias da densidade é pelo estudo do potencial gravitacional e de suas derivadas. A disponibilidade global e a boa resolução dos dados do satélite GOCE, aliadas à disponibilidade de dados de gravimetria terrestre, são ideais para a comparação e classificação das bacias de larga escala, como as bacias sedimentares do Solimões e do Amazonas dentro do Craton amazônico. Foram processados um conjunto de dados, produtos GOCE EGG_TRF_2 Level 2, ao longo das trajetórias do satélite para remover o ruído (shift/drift) nos gradientes da gravidade a partir da técnica crossover (XO). Calculamos a redução das massas topográfica a fim de obter os componentes do gradiente da gravidade e anomalia da gravidade usando modelagem direta com prismas esféricos a partir do modelo de elevação digital, ETOPO1. Desta maneira, a comparação dos dados somente do satélite GOCE com as reduções das massas topográficas referentes aos componentes do gradiente da gravidade permitiram estimar quantidades invariantes que trouxeram uma melhoria na interpretação dos dados do tensor de gravidade. Além disso, comparamos dados terrestres do campo de gravidade com dados do campo de gravidade dos modelos geopotenciais EGM2008 e GOCE...

Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

Blaser, Nicole; Guskov, Sergei I.; Meskenaite, Virginia; Kanevskyi, Valerii A.; Lipp, Hans-Peter
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 23/10/2013 EN
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46.57%
The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons...

New fast least-squares algorithm for estimating the best-fitting parameters due to simple geometric-structures from gravity anomalies

Essa, Khalid S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN
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46.31%
A new fast least-squares method is developed to estimate the shape factor (q-parameter) of a buried structure using normalized residual anomalies obtained from gravity data. The problem of shape factor estimation is transformed into a problem of finding a solution of a non-linear equation of the form f(q) = 0 by defining the anomaly value at the origin and at different points on the profile (N-value). Procedures are also formulated to estimate the depth (z-parameter) and the amplitude coefficient (A-parameter) of the buried structure. The method is simple and rapid for estimating parameters that produced gravity anomalies. This technique is used for a class of geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, the infinitely long horizontal cylinder, and the sphere. The technique is tested and verified on theoretical models with and without random errors. It is also successfully applied to real data sets from Senegal and India, and the inverted-parameters are in good agreement with the known actual values.

Parallel Processing For Gravity Inversion

Frasheri, Neki
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/publishedVersion; info:eu-repo/semantics/bookPart; info:eu-repo/semantics/conferenceObject
Publicado em /10/2015 ENG
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46.05%
In this paper results of recent updates of a simple algorithm for the inversion of gravity anomalies for 3D geosections in parallel computer systems are presented. A relaxation iterative principle was used updating step by step the geosection distribution of mass density. Selection of updates was done on basis of least squares error match of the update effect with the observed anomaly. Locally weighted least squares combined with the linear trend were used to obtain good inversion results for two-body geosections.; Proceedings of: Second International Workshop on Sustainable Ultrascale Computing Systems (NESUS 2015). Krakow (Poland), September 10-11, 2015.

Evolution of the intracratonic Officer Basin, central Australia: implications from subsidnce analysis and gravity modelling.

Haddad, D; Watts, Anthony D; Lindsay, John
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.22%
The intracratonic basins of central Australia are distinguished by their large negative Bouguer gravity anomalies, despite the absence of any significant topography. Over the Neoproterozoic to Palaeozoic Officer Basin, the anomalies attain a peak negative

Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale.

Galindo-Zaldívar, Jesús; Maldonado, Andrés; Schreider, Anatoly
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artículo Formato: 10752 bytes; application/octet-stream
ENG
Relevância na Pesquisa
46.35%
The main features of the deep structure of the Gorringe Ridge are analysed on the basis of gravity and magnetic measurements, as well as seismic profiles, drill holes, rock dredges, submersible observations and seismicity data. The gravity and magnetic models of the Gettysburg and Ormonde seamounts, which form the Gorringe Ridge, suggest that the Moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold. This structure is the result of a northwestward vergent thrust that deformed the oceanic crust, with a minimum slip of approximately 20 km. The activity of the thrust probably started 20 Myr, and produced the recent stages of seamount uplift. The seamount is mainly composed of gabbros of the oceanic crust, serpentinized rocks and alkaline basalts. The large antiform, located in the hangingwall of the thrust, is probably deformed by minor faults. This oceanic ridge is a consequence of the oblique convergence between the African Plate and the overlapping Eurasian Plate.; Peer reviewed

FA2BOUG—A FORTRAN 90 code to compute Bouguer gravity anomalies from gridded free-air anomalies: Application to the Atlantic-Mediterranean transition zone

Fullea, J.; Fernández, Manel; Zeyen, H.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 3505499 bytes; application/pdf
ENG
Relevância na Pesquisa
46.36%
In this paper we present a computer program written in FORTRAN 90 specifically designed to determine the Bouguer anomaly from publicly available global gridded free-air anomaly and elevation database sets. FA2BOUG computes the complete Bouguer correction (i.e. Bullard A, B and C corrections) for both land and sea points in several spatial domains according to the distance between the topography and the calculation point. In each zone a different algorithm is used. In a distant zone we consider the harmonic spherical expansion of the potential of each right rectangular prism representing an elevation grid point. In an intermediate zone we compute the gravitational attraction produced by each prism using the analytic formula. Finally, an inner zone contribution is divided into two parts: a flat-topped prism with a height equal to the elevation of the calculation point, and four quadrants of a conic prism sloping continuously from each square of the inner zone to the calculation point. The program has been applied to the Atlantic-Mediterranean transition zone to obtain a complete Bouguer anomaly map of the area, integrating available onshore Bouguer anomaly with satellite-derived free-air anomaly data. Positive Bouguer anomalies are found in the Atlantic oceanic domain (240–300 mGal)...

New study of the local gravity field of El Hierro (Canary Islands)

González Montesinos, Fuensanta; Arnoso, José; Benavent, M.
Fonte: Universidad Complutense de Madrid Publicador: Universidad Complutense de Madrid
Tipo: Artículo Formato: 711612 bytes; application/pdf
ENG
Relevância na Pesquisa
46.36%
El Hierro island has been built-up at the from a classic triple armed rift system, being its subaerial morphology enhanced by large scale landsliding. The ridges are marked on the Island by frequently aligned faults and volcanic centres. Three volcanic cycles take part in its evolution: Old, Intermediate and Recent Series, which can be clearly separated. The Bouguer anomaly map in this island shows several gravity anomalies which can be associated to the different stages of its growth. A detailed study, increasing the number of gravity stations and improving previous researches, has let us establish a better interpretation of the local gravity anomalies associated with the recent volcanism in the area. To remove the influence of the deepest sources of the gravity field in this local study, we identify a regional trend by a robust polynomial fit. The residual map is analyzed with statistical techniques. The observational noise is filtered distinguishing the signal corresponding to the local gravity field. The inversion of these data is based on a genetic algorithm which optimizes the model of distribution of gravity sources by emulating the Darwin’s principle about evolution. The geometry of these sources is determined upon a prismatic partition of the subsurface...

Anomalías gravimétricas y estructura del abanico aluvial de La Zubia (Sierra Nevada occidental, Cordilleras Béticas).; Gravity anomalies and structure of the La Zubia alluvial fan (western Sierra Nevada, Betic Cordilleras)

Sanz de Galdeano, Carlos; Ruiz Constán, A.; Galindo-Zaldívar, Jesús
Fonte: Sociedad Geológica de España Publicador: Sociedad Geológica de España
Tipo: Artículo Formato: 10752 bytes; application/octet-stream
ENG
Relevância na Pesquisa
46.09%
4 pages, 4 figures.; La Zubia alluvial fan is located at the boundary between the western slopes of Sierra Nevada and the Granada depression. The Alpujárride rocks of the northwestern flank of Sierra Nevada antiform constitute its metamorphic basement. New gravity data allow to estimate the distribution of the Neogene-Quaternary sedimentary fill thickness. Gravity models indicate that the N-S normal faults of Sierra Nevada border have not large related depocenters and the basement is deeper towards the Granada depression. Faults are more active in the northern sector of the alluvial fan, where is located the NW-SE oriented Granada Fault that northwestwards progressively increases its vertical slip.; Este trabajo se ha desarrollado en el marco de una Beca de Iniciación a la Investigación y de Colaboración en la Universidad de Granada. Trabajo financiado por el proyecto BTE 2003-01699 (CICyT).; Peer reviewed

Adjustment of the First Order Gravity Net in Spain

Sevilla, Miguel J.; Gil, Alejandro J.; Romero, P.
Fonte: Universidad Complutense de Madrid Publicador: Universidad Complutense de Madrid
Tipo: Artículo Formato: 1255545 bytes; application/pdf
ENG
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46.33%
Ihe Spanish first order gravity net REDORAES was established in 1973 with the measurements made by combined groups from Ihe IGN (Instituto Geográfico Nacional, Spain) and Ihe DMATC (Defense Mapping Agency Topographic Center, USA). The gravity data were processed by DMATC and results were reported to ING. Since 1974 lo 1977, a scientific cooperation was established between the IGN and the present Instituto de Astronomía y Geodesia (IAG) which proceed lo the analysis of the REDGRAES, and the study of the calibration une and the regional densification trips to get an automatic procedure for computing the gravity anomalies in Spain and the global study of the Spanish gravimetry. Recently these results have been revised lo obtain a data bank of gravity anomalies to be used, in cooperation with the «Instituto di Topografía, Fotogrammetria e Geofísica» (Milano), in Ihe gravimetric geoid determination. As results of this analysis possible errors in Ihe fírst computation and the lack of a statistical analysis have been detected. So, a new adjustment of the Spanish gravity net has been planned using the IGSN 71 stations sited in Spain.; Peer reviewed

STRUCTURAL MODELING OF THE VICHADA IMPACT STRUCTURE FROM INTERPRETED GROUND GRAVITY AND MAGNETIC ANOMALIES

Hernández,Orlando; Khurama,Sait; Alexander,Gretta C.
Fonte: Boletin de Geología Publicador: Boletin de Geología
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2011 EN
Relevância na Pesquisa
46.54%
A prominent positive free-air gravity anomaly mapped over a roughly 50-km diameter basin is consistent with a mascon centered on (4°30'N, -69°15'W) in the Vichada Department, Colombia, South America. Ground follow up gravity and magnetic anomalies were modeled confirming the regional free air gravity anomalies. These potential field anomalies infer a hidden complex impact basin structure filled with tertiary sedimentary rocks and recent quaternary deposits. Negative Bougueranomalies of 8 mGals to 15 mGals amplitude are associated with a concentric sedimentary basin with a varying thickness from 100m to 500 m in the outer rings to 700m to 1000m at the center of the impact crater basin. Strong positive magnetic anomalies of 100 nT to 300 nT amplitude infer the presence of a local Precambrian crystalline basement that was affected by intensive faulting producing tectonic blocks dipping to the center of the structure, showing a typical "domino structure" of impact craters such as that of Sudbury, Ontario, Canada. Basic to intermediate mineralized veins and dikes with contrasting density and magnetic susceptibility properties could be emplaced along these faulting zones, as inferred from local gravity and magnetic highs. The geologic mapping of the area is limited by the flat topography and absence of outcrops/ geomorphologic units. Nevertheless...

Structural deformation in central Cuba and implications for the petroleum system: new insights from 3D inversion of gravity data

Batista-Rodríguez,José Alberto; Pérez-Flores,Marco Antonio; Blanco-Moreno,Jesús; Camacho-Ortegón,Luis Fernando
Fonte: Instituto de Geología, UNAM Publicador: Instituto de Geología, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
Relevância na Pesquisa
46.05%
We propose a new structural framework for Central Cuba based on the 3D inversion of gravity data and constrained by deep boreholes and surface geology. The proposed 3D density model defines structural highs that could work like oil traps for further exploration. This possibility is affirmed by oil wells that are presently productive and that are located on the top of the structural highs in our model. The model also shows the boundaries of several synorogenic basins (Central and Cabaiguán basins) originated by the convergence between the North American and Caribbean plates from the Late Campanian to Late Eocene. The model indicates the location of several sub-basins to the south, as well as the depths and thicknesses variations of the main lithological groups, comprising reservoir and source rocks. The structural framework reflects the geological evolution of the region characterized by the collision and overthrust of ophiolitic rocks and the Cretaceous volcanic arc over the carbonate rocks of the Bahamas passive paleomargin. These geological processes controlled the spatial position and geometry of the different lithological groups, faults and basins.

The structure of the Goulfey-Tourba sedimentary basin (Chad-Cameroon): a gravity study

Nguimbous-Kouoh,J. J.; Ndougsa-Mbarga,T.; Njandjock-Nouck,P.; Eyike,A.; Campos-Enríquez,J. O.; Manguelle-Dicoum,E.
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2010 EN
Relevância na Pesquisa
46.26%
A gravity study of the Goulfey-Tourba basin, southeastern Chad Lake, northern Cameroon, is presented to establish its main shallow crustal structural features. Regional and residual anomalies are interpreted in terms of the available geological information. Spectral analysis and 2.5D modelling of three profiles selected from the residual anomaly map provide depths to basement of 4.0, 2.0, and 2.9 km. These depths constrain the gravity models along the profiles, which indicate that the sedimentary infill is of variable thickness. Thus, we have three sub-basins along the Goulfey-Turba depression: Goulfey, Tom-Merifine, and Tourba. These sub-basins are of tectonic origin. They are associated with the extension tectonics that have affected the region from the Benue trough to the Chad basin. The Goulfey sub-basin is the deepest one. The sedimentary infill is probably constituted by sandy clayey alluvial deposits, sandstones or shales. Depths to basement were constrained with by spectral analysis results. The basement is granite and gneiss, with basaltic intrusions. The inferred faults are of the normal type.

Crustal structure of eastern Cuba, derived by constrained 3D gravity inversion

Arango-Arias,Eduardo Diego; Pérez-Flores,Marco Antonio; Batista-Rodríguez,José Alberto
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2014 EN
Relevância na Pesquisa
46.15%
A three-dimensional crustal model for Eastern Cuba, obtained through a process of gravity data inversion is presented. The study area cover a rectangular area of 64 600 km². The initial model for the inversion was constrained by surface geology, seismic and drilling data. The inversion algorithm uses gravity data to estimate 3-D topographies from the main geological units. The model provides quantitative information on the depths and thicknesses of the geological formations. The resulting model provides new information about the regional composition of the crust. Alien sequences are observed with different compositions and origin over the basement of Bahamas carbonate platform. Most of the maximum gravity anomalies are associated with presence of dense shallow ophiolite sheets. The most remarkable detail is the gravity "southwest" maximum, related to the presence of denser oceanic crust generated in the Cayman spreading center.

Estimation of multiple density-depth parameters from gravity inversion: Application to detached hanging wall systems of strike limited listric fault morphologies

Chakravarthi,V.; Pramod Kumar,M.
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2015 EN
Relevância na Pesquisa
46.51%
An inversion algorithm is developed to simultaneously estimate the fault plane geometry and the parameters pertaining to either densities or depths of multiple geologic formations within the hanging wall system of a strike-limited listric fault from the observed gravity anomalies. Fault planes of the structures are described by polynomial functions of arbitrary but specific degree. The applicability of the algorithm is demonstrated on both synthetic and real field gravity anomalies. In the synthetic example, pseudorandom noise is added to the gravity anomalies of the structure prior to inversion. From the inversion of gravity anomalies produced by a synthetic structure it was found that the estimated parameters more or less mimic the true parameters even in the presence of random noise. The estimated densities and depths of the formations from independent inversion of real-world gravity anomalies from the margin of the Chintalpudi sub-basin in India correlate well with the available drilling information.

A geostatistical re-interpretation of gravity surveys in the Yagoua, Cameroon region

Njandjock Nouck,Philippe; Kenfack,Chamberlin; Diab Diab,Ahmad; Njeudjang,Kasi; Jorelle Meli'I,Larissa; Kamseu,Rodrigue
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
Relevância na Pesquisa
36.46%
Since 1960, many gravity studies have been carried out in the Yagoua region of northern Cameroon. Gravity data was collected over a wide area of approximately 11628 km2. These data are insufficient, irregular, scattered and do not efficiently permit gravity field downward and upward continuations, derivatives and other operations that might require regular gridded data. Some anomalies on the Collignon map (1968), may correlate with known geological structure but do not appear on maps by Louis (1970) and Poudjom et al. (1996). To produce regular gridded gravity data and better control anomalies due to geological structures, the kriging method was applied to a 188-data baseline. Several variogram models were tested for this purpose. It was found that a spherical variogram model is the best; it has produced a new kriging dataset of about 10,100 data and a new map of kriged Bouguer data. This map contains positive anomalies in the Maroua-Mindif and Maga areas on the Collignon (1968) map, which were not present on Louis (1970) and Poudjom et al. (1996) maps. The positive anomalies of Guibi-Doukoula and Yagoua, not separated on the Louis (1970) and Poudjom et al. (1996) maps, show up as clearly distinct as previewed by Collignon (1968).The new results can be used for subsequent gravimetric studies.

Gravity anomalies, sub-surface structure and oil and gas migration in the Mamfe, Cameroon-Nigeria, sedimentary basin

Ndougsa-Mbarga,Théophile; Manguelle-Dicoum,Eliezer; Campos-Enriquez,José-Oscar; Yene Atangana,Quentin
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2007 EN
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46.33%
Preliminary gravity results for the Mamfe Basin in the border region of northwestern Cameroon with southeastern Nigeria are reported. No geophysical studies were available for this important area, which is genetically related to oil and gas deposits in the Benue Trough. Regional and residual gravity components were obtained by least-square fitting of a third-degree polynomial surface to the Bouguer anomaly. The residual anomalies feature two NE-SW gravity lows attributed to sedimentary infill about the localities of Ekok and Agbokem, and about Mukonyong, Mamfe and Bachuo Akagbe. The gravity highs to the north and south are associated with outcrops of the basement complex. This structure corresponds to two major basins separated by a structural high. The deeper western sub-basin comprises two sub-basins separated by a minor structural high possibly related to the crystalline basement. These sub-basins tend to be shallower in the eastern direction possibly indicating the direction of migration of hydrocarbons. More detailed gravity and seismic studies may lead to discoveries of structural or stratigraphic traps. We conclude that the area is a promising prospect in terms of oil and gas prospecting.