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| Author(s): |
Welitom Rodrigues Borges
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto Astronômico e Geofísico (IAG/SBD) |
| Defense date: | 2002-03-22 |
| Examining board members: |
Jorge Luis Porsani;
Vagner Roberto Elis;
Augustinho Rigoti
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| Advisor: | Jorge Luis Porsani |
| Abstract | |
In this work, the Ground Penetrating Radar GPR and Resistivity methods were used aiming at characterize geologically the sediments and the top of the granitic basement of the Sedimentary Basin of São Paulo. Moreover, manual probings a depht of to 5m in order to detail the shallow subsurface and 3 boreholes of approximately 80m of depth were dug as part of this research. The study area is located inside the São Paulo´s University Campus. The Sedimentary Basin of São Paulo has an area of approximately 1800km2 and maximum thickness of 310m. It is characterized lithologically by clays and sands of the Taubaté Group and of the Itaquaquecetuba Formation, reposing, usually, over a granitic basement. The GPR and resistivity data were acquired in two areas, one located in front of the Astronomy, Geophysics and Atmospheric Sciences Institute (IAG/USP) and another near area to the Nuclear, Energy Researches Institute (IPEN). The geophysical profiles were performed along a same line, aiming at comparison of the results obtained with different methodologies. The GPR profiles acquired in front of the IAG/USP, with 200m of length, were surveyed with antennas of 25, 50, 100 and 200MHz. Electric Profiles (EP) were acquired with dipole spacing of 10 and of 20 meters. Moreover, the points of the Vertical Electric Soundings (VESs) were positioned on these profiles. The Schlumberger and Dipole-Dipole array were employed for the VES survey. Based on the processing and interpretation of the geophysical data, and the geological information obtained through boreholes and manual probing holes. It was possible to evaluate the utilization potentiality of the GPR and resistity method at the border of the Sedimentary Basin of São Paulo. The GPR method proved effective to map structures of subsoil down to 14m of depth, identifying the botton boundary of the soil and one coarse sand layer. The thick conductive sediments didnt allow the GPR to reach larger dephts. VESs (Schlumberger array) identified resistive and conductive horizons, correlated with the São Paulo Basin sediments within about 43m of depth. VESs (Dipole-Dipole array) allowed to identify the basement in the area in front of IAG/USP to a depth range from 43 to 47m, dipping NW to the of Campus Municipality. Eletric Profiles (EP) allowed to identify lateral variations in sediments of the São Paulo Formation. The geophysical results present an excellent correlation with the geological information of the boreholes, manual probing holes and a seismic reflection profile. It was concluded that the GPR and resistivity methods are promising for the geological characterization of shallow subsurface mapping at the border of the Sedimentary Basin of São Paulo. (AU) | |