Magnetic anomaly maps reflect the spatial distribution of magnetic sources, which may be located at different depths and have significantly different physical and geometrical properties, complicating the identification of the corresponding geologic structures. Filtering techniques are frequently used to balance anomalies from shallow and deep sources, and to enhance certain features of interest, such as the edges of the causative bodies. Most methods used for enhancing magnetic data are based on vertical or horizontal derivatives of the magnetic anomalies or combinations of them, and the edges or centers of the sources are identified by maxima, minima, or null values in the transformed data. Normalized derivatives methods are used to equalize signals from sources buried at different depths. We present an edge detector method for the enhancement of magnetic anomalies, which is based on the tilt angle of the total horizontal gradient. The notable features of this method are that it produces amplitude maxima over the source edges and that it equalizes signals from shallow and deep sources. The method is applied to synthetic and real data. The effectiveness of the method is evaluated by comparing it with other edge detection methods that have been previously reported in the literature and that make use of derivatives. The results show that our method is less sensitive to variations in the depth of the sources and that it indicates the position of the edges of causative bodies in a more accurate fashion, when compared with previous methods, even for anomalies due to multiple interfering sources. These results demonstrate that the proposed method is a useful tool for the qualitative interpretation of magnetic data.
ABSTRACT. In this paper we present the GRAV MAG PRISM code to generate synthetic gravity and magnetic anomalies from rectangular prismatic bodies with arbitrary dimensions, densities and magnetizations. The code has been developed in a MATLAB/OCTAVE environment and provides a graphical and a numerical output, as well. The data are written in xyz (ASCII) format and can be contaminated with noise. We also summarize the theory and show some examples of the program’s applications. The code can be used for research and educational purposes and is freely-distributed by the authors on request.Keywords: gravity and magnetic anomalies, potential-field modeling, program. RESUMO. Neste trabalho é apresentado o programa GRAV MAG PRISM, o qual gera anomalias de gravidade e magnéticas sintéticas a partir de corpos prismáticos retangulares com dimensões, densidades e magnetizações arbitrárias. O código foi desenvolvido em ambiente MATLAB/OCTAVE, com saídas gráficas e numéricas. Os dados são escritos no formato xyz (ASCII) e podem ser contaminados por ruídos. Neste trabalho também é apresentado um resumo da teoria e alguns exemplos de aplicação do programa. O código acompanha um tutorial e pode ser utilizado para fins educacionais e de pesquisa, sendo de distribuição gratuita através de solicitação aos autores.Palavras-chave: anomalias gravimétricas e magnéticas, modelagem de campos potenciais, programa.
ABSTRACT. Recent research projects on the Guarani Aquifer System (GAS-granular), Paraná Basin, Brazil, have been evaluating the tectonic control and its hydrogeological potential, flow patterns, chemical properties and environmental protection aspects.One of this projects is the present research that has investigated a structured area in central State of Paraná of about 23,000 km2, delimited by coordinates 24◦00’S and 25◦00’S, 51◦00’W and 53◦00’W. The study involves Geographic Information System (GIS) integration of aeromagnetic, geological and structural characterization of lineaments based on Digital Elevation Model (DEM) and Landsat images, hydrogeological and hydrochemical data. Basaltic flows and diabase dikes (NW-SE) of the Serra Geral Formation (Lower Cretaceous) predominate in the studied area. These rocks correspond to the overlying Serra Geral Aquifer System (SGAS-fractured). The purpose of the study is to investigate the structural control on both flow and chemism of SGAS groundwater and also to identify fractures that might represent hydraulic connectivity zones to the underlying GAS. Processing and interpretation of aeromagnetic data using various techniques, useful for enhancing shallow sources, and integration with further remote sensing and geological data, allowed to outline the regional structural framework, which is characterized by a mosaic of tectonic blocks delimited by NW-SE (diabase dykes) and NE-SW (Paraná Basin basement) structures. This magnetic-structural framework was compared with the spatial distribution of hydrogeological and hydrochemical parameters. The integrated interpretations made it possible to recognize the structural control on hydrogeology and hydrochemistry of the SGAS and SAG. The results, presented in a georeferenced map, show the main zones of confinement and/or connection of SGAS and GAS. Keywords: Guarani Aquifer System, Serra Geral Aquifer System, Paran´a Basin, hydraulic connection, aeromagnetometry. RESUMO. Projetos recentes de pesquisa no Sistema Aquífero Guarani (SAG-granular), Bacia do Paraná, Brasil, têm avaliado o controle tectônico e seu potencial hidrogeológico, padrões de fluxo, propriedades químicas e aspectos de proteção ambiental. Um destes projetos é a presente pesquisa, a qual investigou uma área estruturada na região central do Estado do Paraná, delimitada pelas coordenadas 24◦00’S e 25◦00’S, 51◦00’W e 53◦00’W, com aproximadamente 23.000 km2. O estudo envolve integrações em Sistema de Informações Geográficas (SIG) de dados aeromagnéticos, geológicos, estruturais Modelo Digital de Elevação (MDE) e imagens Landsat, hidrogeológicos e hidroquímicos. Lavas basálticas e diques de diabásio (NW-SE) da Formação Serra Geral (Cretáceo Inferior) predominam na área estudada. Estas rochas correspondem ao Sistema Aquífero Serra Geral (SASG-fraturado), sobrejacente. O objetivo do estudo ´e investigar o controle estrutural do fluxo e do quimismo das águas subterrâneas do SASG e identificar também fraturas que possam representar zonas de conexão hidráulica com o SAG subjacente. Processamentos e interpretações de dados aeromagnéticos, a partir de várias técnicas, e a integração com dados de outros sensores remotos e geológicos permitiram a composição de um arcabouço estrutural regional, o qual é caracterizado por um mosaico de blocos tectônicos limitados por estruturas NW-SE (diques de diabásio) e NE-SW (embasamento da Bacia do Paraná). Este novo arcabouço magnético-estrutural foi comparado com a distribuição espacial dos parâmetros hidrogeológicos e hidroquímicos. A interpretação integrada permitiu reconhecer o controle estrutural da hidrogeologia/hidroquímica dos SASG e SAG. Os resultados, apresentados em um mapa georreferenciado, mostram as principais zonas de confinamento e/ou conexão dos SASG e SAG. Palavras-chave: Sistema Aquífero Guarani, Sistema Aquífero Serra Geral, Bacia do Paraná, conexão hidráulica, aeromagnetometria.
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