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Doctoral Thesis
DOI
10.11606/T.18.2018.tde-15062018-181113
Document
Author
Full name
Fábio Soares Magalhães
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1999
Supervisor
Committee
Hasui, Yociteru (President)
Celestino, Tarcísio Barreto
Hennies, Wildor Theodoro
Morales, Norberto
Rodrigues, José Eduardo
Title in Portuguese
Tensões regionais e locais: casos no território brasileiro e padrão geral
Keywords in Portuguese
Tensões locais
Tensões regionais
Território brasileiro
Abstract in Portuguese
Este estudo visou abordar as tensões regionais no território brasileiro e suas modificações em nível local sob impacto de fatores diversos, fisiográficos e litoestruturais. As tensões regionais no território brasileiro, determinadas por análises de sismos, de breakouts de poços petrolíferos e de falhas permitem reconhecer, em caráter preliminar, uma Província de Tensões do Interior e uma Província de Tensões da Costa. A primeira tem σ1 em torno de NW-SE, de regime tectônico transcorrente, que se relaciona com a rotação da Placa Sul-Americana para oeste. A segunda tem σ1 paralelo à costa, de regime distensivo, aparentemente relacionável ao relevo serrano e/ou às bacias sedimentares costeiras adjacentes. As tensões locais, que interessam diretamente às obras de engenharia, representam resultados de reorientação e/ou reajustes das tensões regionais às características internas dos maciços, do traçado da fisiografia e da carga litostática. Pela análise ou reavaliação de dez casos brasileiros, em que se dispõe de tensores de tensão por determinações in situ (sobrefuração, fraturamentro hidráulico) e/ou análise de falhas, foram reconhecidas influências de descontinuidades, anisotropias e heterogeneidades das rochas, da topografia e da profundidade nas modificações do regime de tensão regional. Os resultados consolidados, ainda que de nível preliminar em decorrência da carência de mais dados, mostram que a abordagem das tensões não deve limitar-se a determinações in situ, mas ser mais ampla e considerar os contextos morfológico e geológico-estrutural regionais e locais.
Title in English
not available
Keywords in English
not available
Abstract in English
Regional stress fields in the Brazilian territory and their changes in rock masses by the impact of many local physiographic and litho-structural features in ten areas are analysed in this study. The regional stress field in Brazil, defined by analysis of data from seismic events, breakout of oil wells and cenozoic faults, allows to recognize in a preliminary approach the Inland Stress Province and the Coastal Stress Province. The first one has σ1 of strike-slip tectonic regime trending NW-SE, related to the westward rotation of the South American Plate. The second one presents σ1 of extensional regime oriented parallel to the coast, seemly by influence of the outstandig adjacent relief or marginal sedimentary basins upon the first stress field. The local stress field, which is important for engineering projects, results from reorientation and/or readjustments of regional stresses by influence of the internal characteristics of the rock masses, to the physiographic pattern and to the lithostatic pressure. The ten Brazilian cases here analyzed or reappraised have stress fields obtained from in situ determinations (overcoring, hydraulic fracturating) and/or analysis of faults. The fault sets indicate (1) in some areas a stress field of extensional regime related to the Cretaceous/Lower Tertiary South-Atlantic Reactivation, and (2) a younger and present tectonic regime of strike-slip type. The in situ determinations indicate stress tensor with the same geometry of the regional field, but with position interchanges of the axis. These modifications of the regional stress may be explained by influence of discontinuities, anisotropies and rock heterogeneities, of the topography, and of the determination depth. The results here compiled are preliminary due to the lack of more data than those available for ten cases, but indicate that, beyond in situ determinations, the stress studies request wider approach taking into account regional and local morphological, geological and structural characteristics.
 
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Publishing Date
2018-06-18
 
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