DesG: uma nova metodologia para intervenção e coleta de dados magnetotelúricos / DesG: a new methodology for intervention and it collects of magnetotelluric data

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

This thesis presents two contributions to magnetotelluric data interpretation. The first one is a new MT inversion method, named Geologic-Descriptive Method (DesG) because it explicitly incorporates a priori information, keeping a close correspondence with the standard description of geological features. The user defines by means of geometric elements (points and axes) the skeleton of geological features, and establishes a priori values for the resistivity of the assumed geological bodies. The method estimates the resistivity distribution in the subsurface, which are closest to the specified geometric elements and produce an acceptable fit to the observations. The analysis of an obtained solution may help in modifying the a priori outline for the sources, allowing, in this way, that successive inversions be performed until the solution fit the data and make geological sense. Among the attractive features of the presented method are: (i) the anomalous sources may present a resistivity larger or smaller than the resistivity of the host rocks, (ii) several host rocks, enclosing or not anomalous sources, may be crossed by the traverse, and (iii) the resistivity contrast between the anomalous source and the host rock may be either abrupt or gradational. Tests on synthetic data reveal, among other relevant features, excellent results in estimating the attitudes of variable-dip faults, which are of particular importance in regional tectonic studies, and in delineating diabase sills within sedimentary basins, which represent a severe obstacle in oil prospecting. The method also allows the joint interpretation of the target sources and the sources causing static shift. Tests using data from COPROD2 shows a estimative of the resistivity distribution in agreement with the geological knowledge about the area. The second contribution relates to the design of geophysical experiment. By means of several indicators, particularly the density information matrix, it is shown that one can access the theoretical resolution of the data, which guides the explorationist in carrying out a survey design. The survey design optimization allows determining the most suitable observation locations and periods to produce a more precise delineation of sources, whose locations are approximately known.

ASSUNTO(S)

campos magnéticos dados magnetotelúricos eletromagnetism magnetotelluric data geofisica geofísica eletromagnetismo resistividade de corpos geophysics magnetic fields desg desg

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