3rd International Congress of the Brazilian Geophysical Society

A evaporaçăo e a evapotranspiraçăo săo componentes naturais do ciclo hidrológico, pelas quais a água precipitada pelas chuvas e pela neve, retorna ŕ atmosfera. Do ponto de vista meteorológico săo entendidas como resultante da açăo combinada de uma série de outros elementos: balanço de energia, tensăo de vapor, temperaturo e vento. O conhecimento desses componentes constitui-se em parâmetro importante no estudo da disponibilidade hídrica de uma determinada regiăo. As taxas de evaporaçăo e evatranspiraçăo săo estabelecidas através o estudo do balanço de energia da superfície evaporante, o qual expressa de forma aproximada o princípio de conservaçăo da energia. Através deste estudo, pode-se avaliar os fluxos de calor latente e calor sensível.

O Leplac-Plano de Levantamento da Plataforma continental Brasileira - vem sendo realizado ao longo de toda a costa brasileira, coletando dados de sísmica de reflexăo multicanal, gravimetria, magnetometria e batimetria através dos navios da Diretoria de Hidrografia e Navegaçăo (DHN), em conjunto com a Petróleo Brasileiro S/A (Petrobrás).

Tradicionalmente, a aquisiçăo dos dados gravimétricos nas margens continentais tem sido realizada por gravimetros adaptados sobre plataformas estabilizadas ŕ bordo de navios. Entretanto, a altimetria do nível do mar realizada por satélites, iniciada pelo satélite GEOS-3 em 1975, está modificando radicalmente a forma de obtençăo da anomalia gravimétrica no mar. Enquanto os gravímetros medem o efeito do campo gravimétrico sobre uma pequena rnassa presa a uma mola, a altimetria por satelíte medem o efeito deste campo impresso na superfície do oceano.

One of the goals in planning and designing seismic surveys is to provide adequate spatial sampling. Spatial sampling has an Influence on many aspects of data processing and Interpretation. Since DMO and wave processes like DMO have become almost universal data processing procedures, the Interplay of spatial sampling and these wave-equation processes Is Important! Poor spatial sampling is often observed to affect waveequation processes such as DMO and migration. Inadequate spatial sampling can result for a variety of reasons. Offshore, irregularities are caused by obstructions, cable feathering, and the acquisition environment; on shore, obstructions and the inability to occupy desired stations are problems. However, a more fundamental problem occurs when the acquisition design itself is deficient. Conventional survey-design specifications such as CMP fold and offset distribution are aimed at achieving a uniform stack of the data. Here I develop similar attributes for evaluation of survey geometries that are based on the application of DMO and stack to the data. These new attributes can be anatyzed-as offset, fold, and azimuth now are in current practice. Both the survey design and acquisition quality control phases of seismic surveys can use these attributes to optimize the resulting DMO; stack, and migration. My method is based on previous work on DMO equalization (Beasley and Klotz, 1992). Uke conventional methods, the analysts requires only the survey geometry. It provides an accurate and practical means of assessing the suitability of the spatial sampling of a seismic survey for wave-equation processing.

A plataforma do Amazonas situa-se na porçăo norte da margem continental brasileira, sendo uma regiăo bastante afetada pelo sistema do Rio Amazonas. A margem continental norte brasileira é caracterizada por sua grande extensăo, o que contrasta com a margem continental do sul (Chaves et al., 1979). A plataforma continental apresenta largura razoável na área compreendida entre o Cabo Orange e o Rio Pará, atingindo 300 km em frente a desembocadura do Rio Amazonas, e ocupa mais de 200.000 km2 (Milliman, 1979). A quebra da plataforma ocorre a uma profundidade de 100 m.

Organic matter from plankton bloom, fishes and sewage outflow are common source for generating gaseous sediments. Presence of organic matter combined with high rate of sedimentation are common characteristics of estuaries though creating an appropriate setting for gas generation. The Amazon system at maximum discharge can reach of 354,793 m3/sec (Figueiredo et al. 1993) and sediment transport estimation 1.2 x 10 tons/yr (Mead et al. 1985). Because of the enormous discharge and associated sediment, a submarine delta is being constructed in the Amazon shelf (Figueiredo et al., 1972, Milliman et aI., 1975). Besides sediment Amazon river brings 3.1 x 10 12gC y*ą of organic carbon (Showers and Angle, 1986) and also great nutrients which are mainly used by planktonic community in the continental shelf. Rates of primary production in the shelf using C14 tracer technique measured by De Master et al. (1991) indicate mean values of 5.8 gCm-2d-1 in the high productivity zone. Organic matter incorporated in bottom sediment are reduced by bacteria generating methane gas that may- be trapped or liberated to the water column. Seismic surveys and core collection in the region during Amasseds cruises have indicated presence of gas in several areas as indicated in figure I. This paper presents results of seismic survey during Amasseds cruise III, leg. 2 and coring collection during others Amasseds cruises in the north Brazilian continental shelf. Amasseds is a cooperative, multi-disciplinary research between Brazilian and American universities.

O estudo dos mapas de isópacas da porçăo norte do Platô de Pernambuco e do trecho da Bacia Oceânica do Brasil adjacente, apresenta a evoluçăo geológica-sedimentar mesozóica-cenozóica desta regiăo. O trabalho teve como base a interpretaçăo de todas as seçőes de sísmica de reflexăo perfiladas na regiăo (Fig. I), e faz parte de uma série de pesquisas geofisicas que vem sendo realizadas na área em estudo pelo LAGEMAR/UFF nos últimos anos. As principais sequęncias sedimentares e fases erosivas e/ou deposicionais do platô foram definidas por Alves e Costa (1986) e as da bacia por Costa e outros (1991). Dos quatro grandes refletores detectados no plato e na bacia o mais profundo corresponde ao embasamento cristalino, que segundo Costa e Maia (1986) é de origem continenta/transicional no platô e de origem oceânica na bacia. Os outros tręs refletores do platô e da bacia associamse a discordâncias, que delimitam sequęncias sedimentares definidas em toda a regiăo (Fig.2).

The intracontinental rift basins of northeast Brazil constrain the chronology of breaking up the Gondowanaland between Brazil and West Africa. Besides constraining the timing of rifting, the basins demonstrate that during early stages of rifting, diffuse intraplate deformation may accommodate regional extension, as illustrated by the widespread distribution of rift basins, up to 600 km westwards from the actual passive margin. The basin distribution and geometry were basically controlled by the previous basement structural framework and by rifting kinematics, related to the spatial interaction between the Southern and Equatorial branches of the South Atlantic rift system. The northeast Brazilian rift basins show clear chronologie and tectonic links to progressive deformation that migrated, from south to north, in the Southern branch. Three syn-rift stages are associated with the rift evolution of the Southern branch, distinguished based upon the structural style and basin-fill characteristics. The main rift stage took pIace during the Neocomian-early Barremian Time, with the development of three main rift valleys: (1) the Gabon-Sergipe Alagoas trend (GSA),(2) the Reconcavo-Tucano-Iatoba trend (RTJ),and (3) the Carirl-Potiguar trend (CP).The influence of preeristing crustal weakness, a Proterozoic heritage, is demonstrated by the megashear zones of the Pernanbuco (Brazil) and Ngaundere (Africa), which behav~d like a huge accommodation zone, balancing ertensionat deformation along the RTJ e GSA trends with simultaneous enenslon along the CPtrend. The basins are typically 20-45 km wide, controlled by NESW trending normal faults, roughly perpendicular to the main extension direction. A major change in rifting kinematics occurred during the Neocomian when early rifting deformation developed in the eastern equatorial domain, meanwhile the CP trend was aborted, and the southern branch had the main stretching phase. During the Aptian, rifting occurred throughout the Equatorial branch and Benue trough (Africa), while a transitional eyaporitic sequence developed in the Southern branch (GSA),-and the RTJ trend was aborted. An Albian-Cenozoic marine drift megasequence overlies the northeast Brazilian rift basins eccept by the RTJ trend and some of the CP basins.

Transformada de Radon Parabólica via Transformadas de Fourier

O Prospecto LEPLAC-IV foi o terceiro programa geofisico levantado pelo Navio Oceanográfico Almirante Câmara (ES-500) no âmbito de Projeto LEPLAC, dando seqüęncia a uma açăo conjunta entre Petrobrás e Marinha do Brasil que, até o momento, permitiu a aquisiçăo de mais de 175 000 km lineares de batimetria de precisăo, sísmica de reflexăo multicanal, gravimetria e magnetometria.