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5th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Sep 1997 - 03 Oct 1997
- Location: São Paulo, Brazil
- Published: 07 November 1997
61 - 80 of 416 results
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Caracterizaçăo Hidrogeológica de Microbacia de Monitoramento Ambiental com o Uso de Métodos Geofísicos
Este trabalho apresenta a caracterizaçăo hidrogeológica preliminar de uma microbacia, utilizando-se métodos de investigaçăo geofísica. A área de estudo fica situada no leste do Estado do Espírito Santo, a cerca de 75 km a norte de Vitória. Trata-se de uma microbacia da margem direita do riacho Guaxindiba, onde a Aracruz Celulose está efetuando monitoramento ambiental da cultura do eucalipto.
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Estudio Geoeléctrico Aplicado a la Evaluación de Recursos Hídricos Subterráneos en la Cuenca del Arroyo Pergamino (Pcia de Buenos Aires)
Authors C.M. Sainato, M.C. Pomposiello, G. Galindo and H. MallevilleLos méetodos eléctricos juegan un papel importante en el estudio de agua subterránea, dada la sirnilitud en el modo en que el flujo de corriente eléctric a y de fluido depend en de la conexión y geometriá de los poros en suelos y rocas. Es decir éstos métodos están afectados por la presencia de fluidos conductores en los poros del suelo.
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Geofísica Por Eletroresisti vidade no Assentamento Rural Casas Altas - Eldorado do Incra, Seropédica, RJ.
More LessEste trabalho apresenta resultados parciais do "Projeto Eletroresistividade da Baixada F1uminense, RJ", que vem sendo desenvolvido pelo Departamento de Geocięncias do Instituto de Agronomia da Universidade Federal Rural do Rio de Janeiro, e cujo objetivo tern side a prospecçăo e o mapeamento da regiăo, de forma a orientar com critérios, a extraçăo de materiais de construçăo, bem como na locaçăo mais adequada para poços captadores de água subterrânea necessária a agroprojetos em geral.
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Prospecçăo VLF, Usando Pseudoseçőes de Densidade de Corrente e Resistividade Elétrica no "Karst" do Norte de Minas
More LessÁgua quando comparada a outros minerais é um recurso barato. Isto obriga a exploraçăo geofísica da água, para ser viável, ser também uma atividade barata. De modo que os métodos geofísicos e suas ferramentas de interpretaçăo tem que ser relativamente baratos, portáteis, fortes e eficientes além de rápidos,
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A Contribuiçăo da Geofísica Aplicada para a Locaçăo de Poços Tubulares Profundos
Authors José M.B. Mendes, Jamile Dehaini, Reginaldo A. Bertolo and Cyro Bernardes Jr.A utilizaçăo de metodologia geofísica no estudo de casos envolvendo questőes hidrogeológicas e ambientais, geotécnicas e de mineraçăo jé é bastante difundida e consagrada no mundo inteiro. A escolha do método adequado para o estudo de cada caso é de fundamental importancia, principal mente nos dias de hoje, visto que o grande avanco tecnológico das últimas décadas nos coloca ŕ disposiçăo uma variedade muito grande de equipamentos e formas de investigaçăo. A utilizaçăo de uma metodologia equivocada, no entanto, pode prejudicar a detecçăo do alvo geofísico investigado, devido a incompatibilidade entre as propriedades ffsicas de interesse e a efetivamente medida. Năo săo raros os casos em que a sofistiçăo metodológica tern atuado como componente para 0 encarecimento desnecessário de urn levantamento de dados geofísicos.
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Geoeletrical Monitoring in Nanji Waste Landfill
Authors Hyoung-Soo Kim and Yeonghwa KimNanji Waste Landfill is one of the largest waste disposal site in Korea. The landfill had been dumped without any controls by municipal living wastes and industrial wastes since 1978 to 1992. During the landfilling, there was no controlled procedure to protect contamination of groundwater and soils in the site as well as in the vicinity of the area. The dumped height of landfill is about 90 m and this height is the biggest one of all the waste disposal areas in the world. So the landfill has become a serious social problem. Finally the remedy of the site has been needed to control the highly contaminated groundwater and gas from the landfill and to protect the landsliding for the efficient usage of the site and the vicinity area. This study has been initiated to elucidate the groundwater and subsurface conditions in the landfill.
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Resistivity Monitoring Study to Detect Groundwater Table Change
Authors Hyoung-Soo Kim and Chan HahnResistivity method has been abundantly used in groundwater study. In this study, electrical resisitivity monitoring method was adopted to detect groundwater table change by artificial pumping. Field resistivity monitorings were conducted in the alluvial deposite site in Geum River, Korea and numerical twodimensional resistivity model tests were made by Finite Element Method (FEM). The field site alluvium mainly consists of fine clay, medium sand and small gravel of which diameter is about few centimeters. The basement of the area is brownish biotite granite and the top of the basement is about 25 m depth from the surface. From the core data, it is belived that the basement is impermeable. Pumping test had been conducted continuously for 20 days. The drawdown was made drastically in the beginning of pumping test but there was no significant drawdown after 2 days. Fig. 1 shows the time-drawdown plots during the pumping test. Some discontinuous drawdown data resulted from electric generator substitutions for power supply or measurement errors. The drawdown of groundwater in the pumping well (captioned PW-l in Fig. 1) was about 4 m and that in observed wells (captioned BHI-2, BH1- 3, and BHI-4 in Fig. 1) which are about 5 m distant from the pumping well was about 1 m. The average pumping rate during the pumping test was 1,520 m3/day.
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Interactions Between Sedimentation and Deformation During the Structural Evolution of Salt-Bearing Divergent Continental Margins
Authors B. C. Vendeville, M.P.A. Jackson and S. RaillardDivergent continental margins, like those of the south Atlantic, display a wide variety of salt structures. These include normal faults formed during one or several episodes of moderate to extreme extension, extension-induced reactive diapirs that later grew passively, folds reactivated by younger normal faults or passive diapirs, and passive diapirs subsequently squeezed and rejuvenated by late contraction. We use experimental models and seismic examples to illustrate how this seemingly complex, highly variable structural pattern can be interpreted and explained by relatively simple concepts about the interaction between sedimentation and the two tectonic processes that drive deformation: gravity gliding and spreading. The balance between gliding and spreading is affected by sedimentation and basement tilt.
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Seismic Surveys in the Northeastern Portion of the Paraná Basin
Authors Tereza Higashi Yamabe, Jesús Berrocal and Liliana Alcazar DiogoPreliminary results of seismic refraction and reflection surveys carried out in Nuporanga, located in the NE portion of the Parana Basin, are presented. The objective of these surveys is to determine the local underground geological structure in order to be used to determine hypocenters of focal seismic activity and to assist the ground water exploitation in Nuporanga. Other geophysical methods (gravimetry, geothermics, magnetotelluric and well logging) are being used as complementary tools for this study. Results from the seismic surveys defined a preliminary model beneath Nuporanga with a thin discontinuous layer of soil of no more than 10m thick with Vp=O.32km/s overlying an also discontinuous layer of Bauru Group sediments with no more than 30m of depth and Vp=1.8km/s,underlying it there is a Vp=2.8km1sbed that is a probable weathered layer of volcanic rock of not yet determined thickness, followed by the Geral basalt with Vp=5.1km/s up to depth of around 400m. The Paleozoic sediments were modelled with 1200m of thickness and Vp=4.0km/s to justify the crystalline basement at 1600m of depth with Vp=6.0km/s
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An Integrated Model to Explain the High Conductivity Below LNAPL Plumes in Granular Sediments
More LessA model is proposed for the spatial distribution of electrical earth conductivity in the volume in and around Light Non-Aqueous Petroleum Liquid (LNAPL) spills. Because of vertical and lateral movement of subsurface liquids, the dimension of time must also be included in any model. The subsurface is a complex system and therefore some principles from biology, geochemistry, and hydrogeology are reviewed. A number of contaminant plumes have been recognized (Bennett, et. aI., 1993) emanating from a single spill, each of which may evolve different geophysical properties with time. In the vadose zone is the freelresidual product plume in which sediments have been directly impacted by free hydrocarbons. Surrounding and above this is the vapor phase plume composed of volatiles derived from the free product plume. Below the water table is the dissolved plume where relatively low concentrations of hydrocarbons disseminate into the upper part of the aquifer. The dissolved plume can be subdivided into an aerobic upper and outer boundary, and an anerobic inner core. Another diffuse gaseous plume can be defined in the vadose zone above zones of biologic degradation of hydrocarbons. This plume is enriched in carbon dioxide and may also contain methane, both products of bacterial metabolism. The vadose zone plumes will affect the electrical conductivity in a highly variable manner, depending upon volume of the spill, surface area of the spill, composition of the spill, thickness of the vadose zone, sediment mineralogy, grain size distribution, and rainfall regime. Initially a lowered conductivity may be observed. However, within the residual product and the aquifer plumes, the biodegradation will produce organic acids which very aggressively leach inorganic salts from the soil or sediment grains. Additionally, bacterial evolution of carbon dioxide gas can lead to carbonic acid production in the overlying vadose zone. This will also produce an inorganic leachate.
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Neural Georadar Probing of Stratified Media
Authors Elizeu Pereira Lopes, Luiz Muniz Barreto and Jorge Muniz BarretoA problem of much interest is how to use remote probing to characterise the electrical structure of layered media. The characterisation amounts to finding the electrical constitutive parameters along with the thicknesses of the layers which make up the media. A robust method for solving this problem is proposed. The data set is composed of ratios between vertical and horizontal magnetic fields at four frequencies. The transverse electric polarisation is employed. The reason for using the TE polarisation is that the TE surface wave sends more power into the ground, per unit length of the antenna, than does the transverse magnetic surface wave. Providing all the other conditions are equal, there is more subsurface power to be reflected when the TE polarisation is employed, and thus the signal-to-noise ratio of magnetic wave-tilt data tends to be higher than that of electric wave-tilt data. The wave-tilt method has four important qualities. Firstly, the fact that measurements can be made from aircraft makes rapid and efficient reconnaissance mapping of large geographic areas possible. Secondly, since the wave tilt is a ratio of field quantities, it presents increased immunity to noise and model limitations. Therefore, as long as the field intensities at the logging points are above the noise level, they are independent of the fields at the transmitting antenna. Thirdly, the wave-tilt method can be used at low frequencies, where the depth of penetration is of the order of tens of metres. Finally, the magnetic wave tilt is highly sensitive to lateral anomalies. This fact makes the wave-tilt georadar able to detect geologic-fault zones or ore bodies. A neural network solves the inverse problem of stratified media from magnetic wave-tilt data. The network hinders the calculated parameters from being grievously degraded, owing to noise in the data and model limitations. The neural network automates the resolution of the inverse problem. This permits the characteristic parameters of the probed medium to be known in situ, so that a corrective action can be immediately taken for the survey to succeed. The neural inversion bestows the properties of generalisation and abstraction on the subsurface radar. Therefore, interpreting the results becomes easier.
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Migraçăo de Dados de GPR Ordenados em Afastamento Comum
Authors Reynam Pestana and Marco B. BotelhoA técnica de GPR ("Ground Penetrating Radar") é capaz de obter imagens de alta resoluçăo das camadas próximas a superfície, em meios de baixas condutividades, através do registro de ondas eletrornagnéticas de alta frequęncia refletidas devido aos contrastes de permissividade elętrica do meio. Os tipos de levantamentos mais us ados nas aquisiçőes de GRP săo a aquisiçăo em afastamento comum e a aquisiçăo em ponto médio comum, ou mais conhecida na sísmica como seçăo CMP. Devido a grande similaridade entre os dados de radar e dados sísmicos, principalmente em meios de baixa condutividade (Davis & Annan, 1987), várias eta pas do processamento de dados sísmicos săo aplicadas no processamento de dados de radar. No caso da aquisiçăo em afastamento comum a distância entre as antenas emissora-receptora e normalmente pequena e os dados sao por muitas vezes migrados desprezandose a distância entre as antenas (usando-se os mesmos algoritmos utilizados na sísmica - migraçăo apos o empilhamento).
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Processamento CMP de Dados de Radar (GPR) no Detalhamento da Subsuperfície
More LessA técnica do Radar de Penetraçăo no Solo (Ground Penetrating Radar) se tornou uma das mais importantes ferramentas geofísicas para investigaçăo da subsuperfície rasa. O objetivo final do emprego do GPR na investigaçăo de problemas geológicos é a obtençăo da geometria e, se possível, das propriedades físicas da subsuperfície. Recentemente, tern side aplicados em radar procedimentos análogos aos usados na aquisiçăo e processamento de dados sísmicos de reflexăo. o trabalho de Fisher et al. (1992) é pioneiro na aplicaçăo do processamento em Ponto Médio Comum (Common Midpoint) em dad os GPR adquiridos comafastamento variável entre fonte e receptores. Outros trabalhos, como o de Grasmueck (1994), que obtęm seçőes empilhadas sobre um maciço cristalino fraturado, ou o de Tillard & DuBois (1995), que realiza análises de velocidade para deterrninar a velocidade de propagaçăo da onda eletrornagnética em granitos, calcários e xistos, săo exemplos de como o process amento sísmico pode fomecer informaçőes indiretas sobre as propriedades dielétricas da subsuperfície.
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Electric Field of a Horizontal Antenna Above a Homogeneous Half-Space: Possible Application to GPR
Authors Christoph Baumann and Edson Emanoel Starteri SampaioTo detect buried bodies using a GPR device it is important to know the undisturbed electric field in the receiver antenna at the surface. The simplest model for the undisturbed case is a horizontal antenna, located in air above a homogeneous half-space. In the following, we present the application of a mathematical formalism, according to Goldman (1990), to calculate the induced electric field component in the frequency domain. The calculation is done numerically and the results are compared with obtainable analytical expressions.
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Aplicaçăo das Metodologias GPR e EM34-3XL em Depósitos Aluvionares do Vale do Rio do Sono, Novo Acordo - TO
Este trabalho apresenta parte dos dados obtidos com GPR (Ground Penetration Radar) e EM34-3XL na regiăo de Novo Acordo - TO, num trecho de depósito aluvionar no Vale do Rio do Sono. Nesta regiăo é comum a ocorręncia de pequenos garimpos de diamantes, que incentivou o usa destas metodologias. O objetivo do trabalho é determinar os paleocanais, defmindo a localizaçăo de cascalhos na base dos canais, profundidade do embasamento e espessura da camada de areia que cobre quase todo o pacote aluvionar.
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Imageamento de Subsuperfície (Método GPR) Aplicado nos Afloramentos Turbidíticos de Almada (Ba)
More LessObjetivando a caracterizaçăo geométrica de feiçőes canalizadas depositadas em ambiente marinho profundo, utilizou-se o equipamento GPR (Ground Penetrating Radar) nos afloramentos arenosos grosseiros e conglomeráticos que cornpőem parte da seçăo de preenchimento do Paleocanion de Almada (Bacia de Bahia SuI). Localizado a cerca de 18 km ao norte de Ilhéus (BA), o conjunto destas feiçőes, sedimentadas durante o Maastrichtiano/Campaniano, se constitui na única exposiçăo conhe cida deste tipo de rocha no Brasil. Em algumas bacias, săo rochas reservatório, portadoras de hidrocarbonetos. Após o processamento sísmico dos dados de altíssima resoluçăo obtidos pela ferramenta, procurou-se identificar as principais feiçőes de corte e preenchimento, características e compatíveis com a geometria intema destes canais submarinos.
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Mapping of Structures in Cenozoic Sediments With GPR in Para and Amazonas States, Brazil
Authors William A. Sauck and Jose Gouvea LuizGround penetrating radar (GPR) has been tested at numerous sites in equatorial Brazil. In the Manaus region, Sauck, et.al. (1995a) showed that penetration to as much as 12-14 meters could be achieved with the 100MHz antennae at the six sites which were tested. In the Belem area, Sauck, et.al. (1995b), similarly demonstrated successful use of GPR at four sites representing different geologic and geomorphic environments. The method has had very little reported use in applications to structural mapping, but we show that conditions in Amazonia are generally excellent for deep GPR penetration (more than 15 m) and thus it can be very valuable to assist structural and stratigraphic mapping. The structural geologist is no longer limited to road cuts and outcrops, but can now extend subsurface mapping to areas of thin cover and also to greater depths below the mapped outcrop areas. We describe here the results of preliminary GPR profiling at four different sites in Amazonian Brazil.
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Exploitation of Limestone Quarries in Brazil with Depth Migrated Ground-Penetrating Radar Data
Authors Marco A.B. Botelho and Irshad R. MutfiWe present a methodology involving constant-offset Ground Penetrating Radar (GPR) sections and their depth conversion using the Reverse Time Migration (RTM) method, in order to define the vertical limits and lateral continuity of the horizons of a calcrete profile, from which are produced blocks of dimension stones industrially known as Travertine Marble. It is possible to define the reflector between the hard material used in the industry and the unuseful chalky material. We also present correctly imaged caves and holes inside the carbonate material.
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Towards Dynamic Restoration of Geologic Profiles
By H. KoyiRestoration aims to achieve geometric consistency and kinematic compatibility between deformed and restored sections. Normal restoration does not take account of dynamics. Dynamic restoration requires achieving not only accurate geometric and kinematic restoration, but also requires that account be taken of strain variations (e.g. layer parallel shortening) with depth and due to the different rheological properties of the deformed units and material flow in and out of the restored profile. Models of compresional regimes (accretionary wedges) and salt structures are used to illustrate the significance of layer-parallel shortening and three-dimensional flow of material in dynamic restoration.
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Diferentes Litologias, Diferentes Situaçőes, Diferentes Respostas. A Utilizaçăo do Método GPR como Ferramenta de Suporte ŕ Geologia
Authors Amilsom Rangel Rodrigues and Jorge Luís PorsaniA baixissima divulgaçăo do método GPR (Ground Penetratinga Radar) como ferramenta de apoio a estudos geológicos no Brasil tern mascarado seu enorme potencial de utilizaçăo para esse [lID. Resultados obtidos em testes realizados em diferentes regiőes do país pela PETROBRAS indicam que as possibilidades de utilizaçăo do GPR no Brasil como apoio a estudos geológicas sao imimeras, desde que haja urn bom conhecimento das capacidades intrínsicas do método, urn planejamento adequado dos levantamentos de campo e experiencia de processamento e interpretaçăo.
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