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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
101 - 150 of 462 results
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Estratigrafia sísmica de alta resolução no lago Juparanã, Linhares (ES) - Brasil
Authors R.S. Hatushika, C.L. Mello and C.G. SilvaThe high-resolution seismic stratigraphy into the Juparanã lake, on Espírito Santo state, Brazil, allowed the preliminary acknowledgement of the Quaternary sedimentation in Doce river lower course lake system. It was possible identify two seismic sequences limited by well defined stratigraphic surfaces. The older Quaternary eposits were attributed to arenaceous alluvial sediments, while that overlying deposits had been associated to tabular argillaceous sediments, formed in a lacustrine phase after the damming of the Juparanã lake.
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Influence of Caribbean tectonics across the Eastern Venezuela petroleum basins
Authors M.G. Castillo Vincentelli and H.D. EbertVenezuelan industrial oil exploration has been improving our knowledge of the petroleum systems in the septentrional region of the South American plate.
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Investigações Geofísicas nos Sambaquis Fluviais de Moraes (Miracatu-SP) e Estreito (Itaoca-SP)
Authors M.D. Watanabe, E.B. Rocha and A. RugenskiThis work presents results obtended with application of radiometric geophysical method on the Moraes and Estreito fluvial sambaqui (shellmound), both localizated in Ribeira de Iguape Valley, SP – Brazil.
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Aplicação dos Métodos de Empilhamento CMP e SRC na Seção 50-RL-90 da Bacia do Tacutu
Authors G. Garabito, J. Eiras, M.G. da Silva and M. PorsaniThe Takutu basin, located astride the Brazil-Guyana border, was explored in Brazil by PETROBRAS in the eighties, where was performed seismic surveys of refraction and reflection, and also was perforated two wells. With the development of modern seismic
processing techniques, there is the possibility of reprocessing the old seismic data with the objective to contribute for an improved evaluation of hydrocarbons potential of the Takutu basin.
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Tectonosseqüências da bacia de Taubaté: Uma interpretação Sismoestratigráfica
Authors L. Molinari and L. BorghiThe Taubaté basin is a Cenozoic basin located in the Southeastern part of Brazil, and its evolution has been associated to the process of the South Atlantic opening. Although many studies have been done in this basin several uncertainties remains. Most of the studies is about surface geology resulting in a lack of knowledge about subsurface environment.
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The Joaquim Tavora case study, Parana basin, Brazil : From live oil show to upside potential estimate in a frontier exploration basin
Authors E.M. Meister and C. Edwal VassãoOil exploration efforts in the huge Paleozoic Parana basin of Brazil waxed and waned since 1892 without a commercial discovery. The recent serendipitous find of live oil in a water well at a basin-flank position does demand explorationists´ attention, however. In the Joaquim Tavora area, surface geology, magnetotelluric and airmag surveys point to the existence of large, untested structural traps for the Devonian to Permian section present.
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Análise Quantitativa dos Efeitos Mecanicos de Rifteamento e Sedimentaçao da Bacia do Reconcavo
Authors D.F. Freitas and J.J.C. PalmaIn this study it was developed a tectonophysic modeling program to simulate the mechanical effects related to the rifting and sedimentary infilling of a rift-type basin along its evolution. The program is based on extension models of Kusznir & Egan (1990) and Weissel & Karner (1989).
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Atributos Sísmicos e Interpretação Volumétrica na Identificação de Corpos Carbonáticos na Bacia de Santos - Brasil
More LessSeismic attributes were used in the volumetric interpretation of carbonatic reservoirs in Santos Basin. As a result, it was possible to visualize, map and characterize a series of carbonate bodies, what was not possible in conventional seismic data. The parametrization for the attributes extraction is a very sensitive step in this process and can determine the success of the interpretation.
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A practical and integrated depth migration approach to prospect identification in BMES-11
Authors M. Rhodes, M. Frismanis and B. DalstrømStatoil took over operatorship of block BM-ES-11 in March 2004 with the objective of identifying new exploration prospects near and under salt bodies. An integrated geological and geophysical project was initiated to provide reliable data for prospect generation in the salt flank and sub-salt areas in the southern part of block BM-ES-11, c.f.
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Seismic and magnetic characterization of Varge˜ao Dome Astrobleme, Southern of Brazil
Authors C. Kazzuo-Vieira, A. Penteado Crósta, A. Moreira Silva, A. Schrank, F. Gamboa and M. TygelVarge˜ao Dome is one of the few examples of eroded impact craters (astroblemes) in the South America. This conspicuous circular depression, located at 26 490S and 52 100W, was formed by the collision of a meteorite against the Earth’s surface and has
a diameter of 12.4 km, depicting sharp topographic gradients of up to 150 meters between its outer borders and inner portions.
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Brasil MegaSurvey – A Regional Study of the Campos Basin
Authors H. Edwards, J. Magalhaes Macedo, L. Groves, N. Humpheys, T. Jarratt, A. Smith, C. Lopez and G.A. BattilaniIn the frontier, deepwater province of the Campos Basin, finding hydrocarbon resources proves challenging due to a poor understanding of the stratigraphy, subsurface structure and depositional systems. All of which must be understood in a regional as well as a local context.
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Use of gammaspectrometric airborne data as tool in regional geologic mapping in the Parana State – Brazil
Authors J.H. Boniatti and F.J. Fonseca FerreiraThis paper presents results of the processing of gammaspectrometric data (TC, K, eU, and eTh) from a 300 km2 area to the North of Curitiba, PR. Samples are separated 67 m from each other along 1,000 m spaced, 120 m high flight lines.
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Avaliaçao Geotécnica - Geofísica das Subestruturas da Ferrovia Vitória - Minas (EFVM) Usando o Radar de Penetraçao no Solo (GPR)
Authors M.A. Barsottelli Botelho and C.G. JorgeThe application of Ground Penetrating Radar (GPR) as a Non Destructive Test (NDT) technique for the assessment of railway track bed ballast is presented in this paper. The GPR was applied on Vitória – Minas railroad (EFVM) and it allowed us to detect changes on geometry and composition of the ballast and sub-ballast which were revealed by amplitude and geometry variations of the reflectors corresponding to the air-ballast and ballast-sub-ballast interfaces.
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Modelagem Numérica Espectral Associada a Migraçoes Pré e Pós Empilhamento para Imagear as Estruturas Internas de um Arenito Análogo de Reservatório da Formaçao Água Grande, Bacia do Reconcavo (BA)
Authors O. Neumann and M.A. Barsottelli BotelhoO método geofísico eletromagnético designado por Radar de Penetração no Solo (GPR) é usado para investigar as estruturas internas de um afloramento de arenito pertencente à Formação Água Grande, na Bacia do Recôncavo. O arenito estudado é um afloramento representativo de uma das rochas reservatório de hidrocarbonetos da Bacia do Recôncavo, constituindo assim um chamado análogo de reservatório. A aquisição dos dados de GPR usou antenas de 200 MHz com a configuração de afastamento constante.
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Elements of Electromagnetic Theory for GPR Applications
Authors J.M. Carcione and M.A. Barsottelli BotelhoWe develop some aspects of the electromagnetic theory regarding the application of the ground-penetrating radar (GPR), namely, a model for the composite dielectric constant, the amplitude variations with offset (AVO), the concept of exploding reflector and Backus averaging to obtain the properties of finely-layered media. The electromagnetic properties are obtained by using a generalization of the Hanai-Bruggeman (HB) equation. The HB exponent (1/3 for spherical particles) is used as a fitting parameter for a sand-clay mixture saturated with water.
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Localização de Manilhas de Concreto Instaladas no Sítio Controlado de Geofísica Rasa do IAG-USP Através de Multi-Configurações das Antenas GPR: Resultados Preliminares
Authors R.S. Lima and J.L. PorsaniThis article shows the preliminary results of multi-configurations GPR antennas in order to locate concrete tubes installed in the Shallow Geophysical Test Site or Sítio Controlado de Geofísica Rasa-SCGR of IAG/USP. Four arrays of antennas were used: TE mode (Transversal Electric), TM mode (Transversal Magnetic), and the TE and TM Cross-Polarizations, according to definitions of Radzevicius & Daniels (2000). The results showed that the TE mode was excellent to detect concrete tubes that presented clear reflections, followed by TM mode.
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Polarization Issues in a Recent Sedimentation Environment
Authors J.M. Travassos and S.S. AndréThis work presents the preliminary results of a GPR survey done at Marambaia, RJ. Part of data acquisition gotten in the region will be presented, and will show to the result of multi polarization of a GPR section.
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Simulações Numéricas GPR para Arqueologia: Exemplos de Sambaquis e Urnas Funerárias
Authors S.I. Rodrigues and J.L. PorsaniIn this article, numerical simulation of GPR results are presented in order to detect human bones and funerary urns inside of carbonate shell layers (sambaquis), as well as to locate structures of dunes and water table. The results showed that human bones and funerary urns can be detected, however, they presented the same reflection pattern, not being possible to differentiate them. The structures of dunes and the water table also are identified, but depend on the electrical conductivity of sambaquis layer, which is underlying dunes. The obtained results are significant and will serve of base for future field works. Moreover, it shows the importance of numerical modeling as an auxiliary tool in interpretation of data, decreasing the uncertainties in interpetation process.
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Processamento de dados GPR registrados na Lagoa do Abaeté pelo método de empilhamento CRS
Authors G. Garabito, M.A. Barsottelli Botelho and T. DouradoThe Common Reflection Surface (CRS) stack method is suite to simulate a zero-offset section with high quality and high signal-to-noise ratio from multi-coverage reflection seismic data. This seismic imaging method is fully automatic and it may be applied to irregular geometry data. We present the first results of the application of the Common Reflection Surface (CRS) method based on global optimization to simulate a zero offset stacked section from multi-coverage Ground Penetrating Radar (GPR) real data. We lso present a comparison of the results of the CRS processing with the conventional NMO processing. The results show that the CRS processing provided a zero-offset stacked section with better resolution.
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Utilização do Geo-Radar nos trabalhos de escavação do Sítio Teixeira Lopes, Juiz de Fora, Minas Gerais, Brasil
Authors P.R.A. Aranha, A.P. de Paula Loures de Oliveira and C.H.B. RochaThis paper shows the GPR's results of its application on the study of the Teixeira Lopes Archeological Site, Juiz de Fora, Minas Gerais, Brazil. The excavation works took place in October 2004, in an attempt to verify archeological evidences that resisted the destruction of the site during the opening of two silos, in 1982. The material remains, as ceramic fragments and quartz chips, were quite deteriorated. In order to dinamize the work the area was profiled with the GPR (Ramac) through parallel lines 1 m apart, with 400 MHz antenna set, and interval acquisition at 0,05m. The radargrams detected some anomalies that were checked in loco and identified as wires, plastic, garbage, and others. This demonstrates that the Site is being even more disturbed since the 1982. Afterall, the GPR showed success in the application in this research.
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Finite difference modeling of 2D GPR data considering attenuation
Authors M. Heimer, M.A. Barsottelli Botelho and S. Pomponet OliveiraWe use a finite-difference scheme to simulate 2D ground penetrating radar data by solving the damped wave equation. We show that the stability condition for the damped scalar wave equation does not depend on the damping factor. As an example application of our modeling tool we investigate a typical situation in granite prospecting, where a conductive clay overburden masks the real position of the fractures in the granite. The results of the modeling have a good agreement with the actual data. Also, the algorithm shows well the increase in attenuation with the increase of the frequency. The algorithm shows to be a good basic modeling tool that can be used for further applications and for comparisons with other modeling methods like pseudospectral or finite elements.
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Utilização do GPR 3D bi-polarizado na localização de um BOP soterrado devido a colapso de terreno no Campo de Fazenda Belém, Bacia Potiguar
Authors P.X. Neto and W.E. de MedeirosO GPR utiliza antenas para irradiar a energia eletromagnética para o meio geológico. Esta energia, ao se propagar no meio geológico, sofre reflexão quando encontra interfaces com contrastes de impedância eletromagnética (interface litológica, objetos enterrados, etc) e é recebida pela antena receptora. A energia refletida por um alvo é função da amplitude e da direção de vibração (polarização) do campo eletromagnético incidente. Isso implica que o receptor é sensível à direção de vibração do campo eletromagnético e, portanto, sensível à morfologia ou disposição espacial do alvo.
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Interpretação em 3D de Dados de GPR em Estação de Interpretação de Dados Sísmicos
Authors A.J. Pereira, L.A.P. Gambôa, M.A.M. da Silva, A.R. Rodrigues and A. da CostaCom a conversão dos dados de GPR adquiridos em formato próprio, para um formato seg-y genérico passível de carregamento em estação de interpretação sísmica, foi possível a visualização em 3D de feições representativas da estratigrafia de um trecho da praia de Itaipuaçú, município de Maricá, Estado do Rio de Janeiro. Essa possibilidade permitiu a identificação nos perfis de feições correspondentes a canais que alimentavam uma paleolaguna, hoje colmatada, no reverso do cordão arenoso externo, além de estruturas análogas às feições observadas atualmente no pós-praia da referida praia, como por exemplo paleoescarpas de tempestades. Outra constatação foi verificar, ao longo de toda a planície mapeada, o lençol freático que ocorre em torno de 5 m de profundidade.
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Monitoramento da umidade de campo empregando a técnica de radar GPR
Authors N.S. Amparo, S.L. Machado, T.C. Dourado and M.A.B. BotelhoThis paper intends to evaluate the GPR potential of use aimed to obtention of water contente profiles in the vadose zone. In order to do that, a laboratory mechanical apparatus was developed in way that constant mid point tests can be perfomed, allowing the obtention of precise CMP radagrams. The apparatus, a sand box wit nominal dimensions of 1 x 0,7 x 0,7 m, had a mechanical device that assures equal displacements from central point. Laboratory tests were performed in order to calibrate equipament and obtain experimental data correlating soil water content and pulse travel velocities theoretical equation, develop inside the scope of the research program, was used in order to predict the relative amounts of water and air in the soil voids.
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Towards cost-effective 3D imaging with GPR
More LessThere are two situations that can motivate a GPR user to perform the investigation in a 3D mode rather than in the conventional 2D mode. The first case is when the 2D approach is not enough to achieve a reliable answer to a specific problem while 3D imaging has the potential for solving the problem correctly.
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Experimentos em Laboratório (1 GHz) e Trabalhos de Campo (200 MHz) com GPR Usando Corpos arenosos para Avaliar a Influência da água e de Hidrocarbonetos na Velocidade e na Amplitude da Onda Eletromagnética
Authors T.C. Dourado, M.A. Barsottelli Botelho, S.L. Machado and N.S. AmparoWe analyse GPR measurements (1 GHz) which were carried out on a well sorted, clean sand in a laboratory experimental site and we also executed AVO field experiments, both using TE and TM- mode configurations,. The AVO works were conducted on a sand dune field around the Lagoa do Abaeté (Salvador, Brazil).
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Detecting cavities and archaeological remains with GPR
Authors E.U. Ulugergerli and S. KadiogluTwo examples were considered in this presentation; detection of cavities in limestone, delineation of boundaries of an archeological remain using Ground Penetrating Radar (GPR) method and affect of the trees on the GPR data. The GPR method has been successfully applied to detect and map underground cavities in Limestone in a reservoir area of a dam being built in southeast Turkey.
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Multi-offset GPR surveys for complex targets
Authors L. Baradello, J.M. Carcione and D. Nieto YabarDuring the last twenty years Ground Penetrating Radar (GPR, georadar) has been successfully used to discover and map several subsurface structures. The mono-static georadar (one single antenna) is fast and inexpensive for these surveys. Often, in archaeological and geological investigations the structures can be very complex: ancient walls and debris in chaotic mixtures of sediments or fractures in rocks. These cases are difficult to interpret with conventional single-offset (SO) records because there is scattering and poor signal-to-noise (SN) ratio. The present paper shows how the GPR multi-offset (MO) technique can provide more information about complex targets and enhance weak reflections. We compare the multi-fold (MF) stack and the MO section to investigate which method gives the best performance.
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Imaging an hyperpicnal turbidite outcrop in Almada Basin (Brazil)
Authors M.A.R. Ceia, A.A.G. Carrasquilla and J.M. TravassosIn onshore Almada Basin, northeast Brazil, sandy and/or conglomeratic turbidites and shales outcrops of Urucutuca Formation occur. These rocks are part of an exhumed portion of the filling-section of the Almada Canyon, which is well mapped by seismic studies in offshore part.
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GPR simulations for pipeline oil drainage detection
Authors M.A.R. Ceia and A.A.G. CarrasquillaPipeline detection and investigation of leakage and fluid drainage play a major part in geophysics applied to downstream problems. Oil drainage may have impact in contaminating subsurface environment, and by consequence, affect socially and economically the nearby population. When that hazard occurs, it could be mapped by geophysical techniques. The strong contrast in electrical properties between oil (or gas), metallic pipes and sediments, makes GPR (ground penetrating radar) one of the best techniques to be used for mapping oil drainage and for pipeline detection.
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Estratigrafia de Alta Resolução da Formação Coqueiro Seco (Bacia de Sergipe-Alagoas) Através da Interpretação de Dados GPR
Authors P.T.L. Menezes, J.M. Travassos and L.S. FrancoA major problem related to carbonates reservoirs is the heterogeneity of porosity and permeability systems. Reservoir analogues can provide valuable definitions of geometric and petrophysical heterogeneities at inter well scales. Integration of ground-penetrating radar (GPR) surveys with sedimentological and stratigraphic data provides information on the internal heterogeneities of sedimentary sequences.
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GPR aplicado ao estudo de Reservatórios Análogos. Estudo de caso em Cordões Litorâneos do Delta do Rio Itapemirim (ES), Resultados Preliminares
Authors G.M. Sousa, P.T.L..J.C. Della Fávera and M.A.M. MedeirosClastic reservoirs analogues based on the interpretation of GPR data provide valuable definitions of geometric and petrophysical heterogeneities of sedimentary sequences at scales that allow dissection of the 3-D anatomy of clastic depositional systems.
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Discussão do conceito de Skin Depth e estimativa de parâmetros elétricos considerando os efeitos de polarização envolvidos a partir de medidas com GPR
The authors analyze, in this work, the polemic question of the signal, being measured by GPR, coming from depth greater than the plane wave skin depth. They conclude that signals are being measured, reflected from depths of the order of five times the skin depth for the 100 MHz frequency being used. They also estimate the dielectric constant for the mapped geologic formations using GPR.
More realistic values of K are obtained, for considering: a) the squared index of refraction, (c/v)2, as due to the electronic polarization, associated to the rock matrix, KM; b) the orientational polarization for the saline water, equal to 78, being considered for the water saturated pore spaces of the rocks, Kf. The mixed relation for a two components material was then used for the finalestimation.
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Aquisição e Processamento em Dados de Ground-Penetrating Radar (GPR) COS e Split-Spread
More LessAquisições de dados de GPR common offset (COS) (monocanal) e split spread (multicanal), com antena de 100 MHz foram realizadas em um afloramento com uma seção geológica que é marcada por variações estruturais na forma de um graben. Os dados de radar foram processados com o pacote Vista 2D/3D seguindo um fluxo de processamento de pré-empilhamento com edição dos dados, correção estática, escalonamento, filtro variável com o tempo, análise de velocidade, correção NMO, mute, e pós-empilhamento com escalonamento, filtro variável com o tempo, filtro multi-canal e migração. As seções finais são apresentadas em profundidade com os dados split-spread fornecendo uma maior representação das feições estruturais e litológicas do afloramento em comparação aos dados COS. A análise das técnicas de processamento de dados sísmicos para os dados de GPR em afloramentos vem a colaborar para o estudo de reservatórios em grandes profundidades, auxiliando em ajuste de parâmetros e verificando a eficácia dos processamentos sísmicos.
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Emprego do GPR para a Caracterização da Morfologia do Fundo e Espessura dos Depósitos da Represa de Guarapiranga, São Paulo / SP
Authors Renato Hochgreb Frazão, Jorge Luís Porsani and Renato Luiz PradoGuarapiranga reservoir is one of most important raw water reservoir for the city of São Paulo locate in an area of high population density in SE Brazil. It is responsible for 20% of potable distribution water. During the last decades the reservoir is experiencing a growing eutrophication process due to untreated sewage discharge. Preliminaries Ground Penetrating Radar (GPR) investigations were carried out in area of Guarapiranga reservoir by determine water depth and perform sub-bottom sediment profiling. Accurate periodic information on the elevations the top of sediment and top of original reservoir bottom is important to calculate the volume of sediment to be removed and to establish the reference elevations for the proposed dredging activities. The measurements are non-intrusive and non-destructive, and were conducted along survey lines. Compared with other geophysical methods, GPR profiles have a very high resolution. The selection of the optimum radar frequency is essential to obtain a good resolution and sufficient depth penetration. The obtained results are very interesting.
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Geologia Estrutural da Bacia Potiguar com base em dados aeromagnéticos
Authors Marcos de Barros Munis and Renato Lopes SilveiraThe E&P Data Bank - BDEP - is the trustee depositary of all geophysical project concerned with E&P activities in Brazil. Especulative data and proprietary data has a confidentially term of 10 or 5 years, respectively. After that, they became public and can be acquired by companies, universities, and others interested by a small price, aiming the further development of oil prospecting knowledge or either production.These public data are available for all the mineral and oil community in CD media. With the development of softwares on processing and filtering geophysical data, good opportunities are open to all. This paper deals with a fast treatment of aeromagnetic data from Bacia Potiguar, NE Brazil, with an improvement on signal / noise ratio giving new ways on structural geologic interpretations using upward continuation, first derivatives and pole reduced maps.
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Modelagem numérica de dados tensoriais de aerogradiometria gravimétrica 3D
More LessAir-FTG is nowadays the only existing airborne full tensor gradiometer technology that is flown for both detailed and regional surveys. The system takes real-time measurements of the differences in the gravity gradient field in three orthogonal directions and at me time compensates for bias in the orientation and movement of the aircraft. Each one of these measurements is related to either density contrasts or geometry of discrete bodies. In this work we elaborate a numerical algorithm to compute the five synthetic gxx, gxy, gxz, gyy and gyz independent tensor components. Results show that gradiometer depict a more observable advantage for identification of nearsurface targets, revealing structures such as lineaments, edges, corners and as a consequence body hapes and thickness. It is also shown that the best images of the subsurface rocks acquired by the air-FTG platform can provide more realistic information than the conventional vertical ground gravity field instruments when interpreting lateral density contrasts.
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Modelamento do sinal gravimétrico e aeromagnético das Alcalinas de Morro do Engenho, sudoeste de Goiás
Authors Alanna C. Dutra and Yára R. MarangoniA 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 Complexo Morro do Engenho (ME) está ao norte da província e constitui uma intrusão circular zonada de cerca de 5 km de diâmetro em superfície. As anomalias gravimétricas variam de +15 a +30 mGal com relação ao campo gravimétrico regional, enquanto que as anomalias aeromagneticas são da ordem de ±3000nT. O modelamento usando a técnica de inversão indica espessura variando de 10 a 12 km, com circunferência média em torno de 10 km. No modelamento conjunto 2,5D, o sinal aeromagnético parece ser gerado por um corpo de geometria cilíndrica vertical. Este corpo geométrico apresenta-se homogêneo e com profundidade compatível com os modelos gravimétricos.
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Interpretação geológico-geofísica de estruturas continentais e sua continuação em águas rasas na Bacia de Campos, Estado do Rio de Janeiro
More LessThis work presents the preliminary comparative analysis of the regional structures observed in onshore satellite images and their continuation toward the Campos Basin shallow water platform. These results were obtained by integration of aeromagnetic and gravimetric data, satellite images, topographic, and regional structural maps, combined with structural analysis from fieldwork.
The southern portion of the Campos Basin is located over gneissic rocks of the Cabo Frio Tectonic Domain (CFTD), a Cambrian-Ordovician tectonic unit formed during the agglutination of the Gondwana Paleocontinent. All the CFTD lithotypes are tectonically intercalated throughout thrust zones, dipping between 5º and 30º to the south. These units were deformed during D1 and D2 deformation stages, at c.a. 520 Ma (Schmitt et al., 2004). The CFTD was juxtaposed to the tectonic units of the Ribeira Belt during D3 phase. The contact is marked by a thrust fault striking NE-SW that dips 30º to the south, with a vergence towards the NW. This regional structure is present in the Macaé region, from where, supposedly, it inflects in an ENE-WSW direction towards the continental platform, with a predominant NE-SW strike related to Early Cretaceous syn-rift fault trends.
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Interpretação de Dados Aeromagnetométricos na Região do Gráben de São João, Rio<br>de Janeiro, Brasil
More LessSeveral anomaly-enhancement techniques were applied to high-resolution airborne magnetic data of the São João Graben, offshore Cabo Frio platform. That approach allowed the identification of several subtle basement faults and the definition of the tectonic framework.
We idendifiyed new NW-SE faults associated to Early Cretaceous transfer zones that segment the obliquely rifted Atlantic margin. That segmentation has important implications for risk factor of deep-water petroleum systems of Campos Basin.
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Estimating basement faults with vertical slips using gravity inversion in onshore Almada Basin, Brazil
More LessWe illustrate that the depth imaging of the fault plane may be obtained using gravity data. Our approach is based on a method that enhances the estimated relief resolution as compared with methods incorporating smoothness constraints. Our results using gravity data from Almada Basin, Brazil, produced an interpretative depth image of the faults compatible with the available seismic data interpretation.
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Radial inversion of 2D potential field data
Authors Valeria C. F. Barbosa and João B. C. SilvaWe propose a new 2D method for inverting potential field data with model constraints designed by the interpreter. Our method uses an interpretation model consisting of a source with polygonal cross section whose vertices are described by polar coordinates with an origin inside the source. With this coordinate system, constraints in an inversion are easier to develop and apply. Our inversion method assumes a known physical property contrast for the source and estimates the radii associated with the polygon vertices for a fixed number of equally spaced angles from 0o to 360o. A wide variety of constraints may be used to stabilize the solutions by introducing information about the source shape. The method recovers stable solutions whose shapes range from almost circular or pear-shaped to elongated in one or more directions.
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Gravity inversion in a user-friendly environment
Authors João B. C. Silva and Valeria C. F. BarbosaIn a user-friendly environment we present a method for inverting gravity data produced by multiple, complex and interfering 2D gravity sources having arbitrary shapes and arbitrary, but known density contrast. Our method is stable and is suitable to recover a complex 2D density distribution, leading to a reliable delineation of sectionally homogeneous sources with complex shapes. It is a method similar to interactive modeling but differs from it in automatically fitting the observations and in requiring from the interpreter only the knowledge of the outlines of the sources expressed by simple geometric elements such as points and line segments. Each geometric element operates as a skeletal outline of a particular homogeneous section of the gravity source to be
reconstructed. Also, the interpreter can define the geometric elements in an interactive way without worrying about the data fitting because it is automatically done. The examples with synthetic data illustrate the good performance of the method in mapping the complex geometry of gravity sources. The solution sensitivity to uncertainties in the prior information shows that to produce good results, the uncertainty on the contrast density of each homogeneous extent of the source should be smaller than 40 percent. The method was also applied to two sets of real data. The first one consists of several positive anomalies produced by metabasalts and metagabbros from a greenstone belt located in Rio Maria region, in Pará state, Brazil. The second one is a negative gravity anomaly produced by the Bodmin Moor Granite, which is part of the Cornubian Batholith in southwestern England. The estimated density contrast distribution in all tests demonstrates a good correlation of the estimated gravity sources with corresponding known geological features.
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Inversão gravimétrica usando regularização entrópica
More LessWe present a new gravity inversion method, which produces an apparent density contrast mapping on the horizontal plane, based on the combination of the minimization of the first-order entropy with the maximization of the zeroth-order entropy. The interpretation model consists of a horizontal grid of 3D vertical prisms, and the parameters to be estimated are the prisms density contrasts. The maximization of the
zeroth-order entropy is equivalent to the global smoothness constraint whereas the minimization of the first-order entropy favors solutions presenting abrupt borders, so a judicious combination of both constraints may lead to solutions characterized by regions where the estimated density contrasts are virtually constant, separated by abrupt discontinuities. The method has been applied to synthetic data simulating the presence of intrusive bodies in sediments. The comparison of the results with those obtained with the global smoothness constraint applied to the same data, showed that that both methods locate the sources with good precision, but the entropic regularization delineates the contour of the bodies with greater resolution, even in the case of 100 m wide bodies separated by a distance as small as 50 m.
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Crustal and tectonic features of northeast of São Paulo State and southwest of Minas Gerais State based on gravimetric studies in southeast Brazil
More LessThis paper presents the results of a geophysical study carried out at Northeast of São Paulo State and Southwest of Minas Gerais State (an area 80 km wide and 97,5 km long) in SE Brazil. The Bouguer anomaly map, geological and structural data allowed to identify three different gravity domains related to the structural pattern (crustal blocks limited by major discontinuities) in the area. These discontinuities were interpreted as geosuture zones lying under the Paraná Basin sediments and have their extends in the Pré-Cambrian Basement. The crustal discontinuities named Alterosa and Ribeirão Preto may be seen as A - type collision sutures with triple junction arrays. Two linear proeminent anomalies are recognized in the Bouguer anomaly map, the limit between the Brasília and São Paulo crustal blocks or paleoplates, the Alterosa suture is deduced in a NW-SE trend, and in a NE-SW trend is the Ribeirão Preto suture. The produced Bouguer anomaly map provides subsidies and information to new concepts and theories to the refinement of tectonic models.
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Gravimetric study in the northeast portion of Paraná Sedimentary Basin – Southeast Brazil. A preliminary Bouguer anomaly map
This paper presents the results of a geophysical study carried out at Northeast of Paraná Sedimentary Basin. Since the first geological surveys and studies with the aim objective to discover oil reserves the structural highs named Pitanga and Pau D’Alho were at the time the principal targets in subsurface and surface studies and prospecting. Such structural highs are evidences from the tectonic and geological evolution from the Paraná sedimentary basin and its related oil occurences. Potential geophysical methods such as gravimetry is a valuable tool in the understanding this structural domes and its evolution through the basin evolutionary story. This study is currently in its inittial phase but a preliminary Bouguer anomaly map provides a better visualisation and allows new concepts and theories of the polyphasic basin story.
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Aquisição e interpretação preliminar de dados gravimétricos do SE do Craton S.Francisco
Authors Luiz Gustavo Rodrigues Pinto, Naomi Ussami and Nelsi Côgo de SáA total of 176 gravity data was acquired, between coordinates 39° to 49°W and 17° to 23°S situated in SE São Francisco Craton. The position of each gravity station was obtained using GPS relative positioning method. The new data was added to the gravity data-bank of IAG/USP. A total of 12,339 stations were processed and preliminarily interpreted. The geology of this area is represented by Archean and Proterozoic metamorphic terrains of SE São Francisco Craton, including the Araçuai and Ribeira fold/thrust belts.
In order to separate shallow from deep sources of gravity field, a 50 km upward continued regional field was removed from Bouguer anomaly map. The residual gravity field from the Quadrilátero Ferrífero was correlated with the exposed geological units. Two main sources were mapped, the Archean metamorphic complex and Rio das Velhas Supergroup.
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A Superfície de Curie na Região Bahia Sul – Análise Espectral sobre dados<br>Aeromagnéticos de Alta Resolução
Authors Glauco Bragança and Luiz F.S. BragaIn this study we used spectral analyses over the High Resolution Airborne Magnetic (HRAM) data, acquired by Fugro-Lasa over the offshore Brazilian basins located in southern region of Bahia State. Depths do the Curie Surface were estimated and they allowed an investigation on the present thermal state of the various compartment of the studied area. Special care was taken on the investigation of the minimum size of the data window that may be used without compromising the reliability of the estimates. Additionally, we compared the regional behavior of the depths to the Curie Surface with the known structural setting of the Camamu-Almada, Cumuruxatiba and Jequitinhonha basins which brought insights on the correlation between the present thermal gradients and the Oil and gas potential in those basins.
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Airborne geophysical data as an aid to geological mapping and target selection in the<br>Tapajós Gold Province, Brazil
More LessAirborne geophysical data acquired over the Tapajós Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatumã Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajós provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiú-Cuiú arc.
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Expressão gravimétrica e aeromagnética dos compartimentos e limites tectônicos da Província Borborema, Nordeste do Brasil
Borborema Province (BP) has a very complex history, but up to now, few geophysical data have been used to constrain its evolution history. This paper presents the first integrated gravity/magnetic/geological data interpretation of the tectonic framework of the province. BP is a Proterozoic fold belt extended between the São Luis - West Africa and São Francisco - Congo/Kasai cratons. Currently, as a result of an increase in geochronologic data, there is growing evidence that its evolution has occurred by a mechanism of terrane collage. This evolution model suggests that large crustal blocks were put together during Meso and Late-Proterozoic events, resulting in crust growing by the arrival of pieces of crust or by the addition of new crusts. Interpretation of regional magnetic and gravity maps revealed the boundaries between crust blocks or compartiments inside BP. As result of the integrated interpretation, it is proposed that BP is formed by the union of at least 11 crust blocks. Boundaries between these blocks form long lineaments in NE-SE direction, in some cases showing vergences to E-W direction. The major block to the south of BP is the São Francisco Craton. The boundary between BP and the craton is still a controversial question, but the geophysical data suggest that N-S lineaments, which occur inside the craton, prolong below Riacho do Pontal and Sergipano hrust fold belts, which are part of BP. In this way, the plate associated to the craton lies beyond its geologically mapped north limit.
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