Welitom Rodrigues Borges

O sítio controlado de geofísica rasa do IAG/USP: instalação e resultados GPR 2D-3D

The data interpretation from shallow geophysical survey can be complex because the uncertainty about subsurface targets. To reduce the ambiguity and help in the interpretation of geophysical data, the Shallow Geophysical Test Site of IAG-USP (Sitio Controlado de Geofisica Rasa-SCGR do IAG-USP) was installed inside the campus at USP. Different targets at various depths were installed along seven lines. The targets buried in the Test Site simulate targets found in geotechnical, archaeological, and environmental studies. In this article, the construction methodology of the Test Site and some GPR results along a line characterized by empty metallic tanks are presented. The geophysical characterization in controlled field condition allowed the calibration of geophysical responses due to known targets, such as, metallic tanks. 250 MHz GPR profile showed an excellent agreement with a GPR 2D model determined by finite difference in time domain method. Fk-migration improved the resolution and the spatial position of the metallic tanks. GPR 3D results, such as 3D cube, fence diagrams, and depth slices, were very important to improve the characterization of the targets in subsurface. SCGR-IAG revealed itself as important tool for teaching, research and extension activities in university related to Geophysics, and it will be very important to our community. With the installation of this Test Site, an important step was done in searching the State of Art in Shallow Geophysics in Brazil, were the development of news equipment, modeling and inversion software could be tested and its response calibrated.

Aplicação de métodos geofísicos para identificar áreas contaminadas por resíduos de um curtume

The main problem on environmental investigations is the determination of contaminated extension area. This work exhibit some results obtained with the geophysical methods applied to locate potentially contaminated areas with tanning residues. The area is located near to the city of Varzea Grande, Mato Grosso State. It was now interdicted and disabled for the residues deposition. The data were acquired from electrical profiles, with inline dipole-dipole array and 4 m spacing electrodes, allowing 5 investigation depths. The data of apparent electric conductivity were acquired in 2 dipole modes (horizontal and vertical coplanar) with intercoil spacing of 10 meters. The 200 MHz unshielded antennas were used to collect GPR data. The station interval to each 0.25 meters and 128 stacks. The areas were classified in Contaminated Area - AC - (sa > 40 mS/m, r 50 ohm.m and low attenuation of GPR). The integrated results allow the contamination maps elaboration, indicating a potentially contaminated area with a preferential NW-SE flux. The geophysics and geological information showed an efficient preliminary analysis in the identification of contaminated areas.

Evaluation of mafic dyke swarm continuity under the Joaquina dune field with ground magnetic survey

ABSTRACT: A ground magnetic survey in a Central-East area of the Santa Catarina Island tested the continuity of the Cretaceous ma-fic dykes beneath the aeolic sediments of the Joaquina plain. Vertical gradient measurements taken in 1880 stations did not detect any magnetic anomaly related to subsurface dykes. Four magnetic profiles located to the north and south of the main area showed the magne-tic signature of various dykes some of them already mapped (north profiles), but also some in subsurface (south profiles). These results suggest that the dykes probably were shallow and truncated, and were already eroded along with the crystalline basement. KEYWORDS: Dyke swarm; Santa Catarina Island; Geophysical mapping; Ground surveys; Magnetic methods. RESUMO: Um levantamento magnetico terrestre foi realizado numa area do centro-leste da Ilha de Santa Catarina, para verificar a con-tinuidade dos diques em subsuperficie na area das dunas da praia da Joaquina. Medidas de gradiente vertical em 1880 estacoes nao revelaram nenhum sinal relacionado com anomalias magneticas produzidas por diques em subsuperficie. Quatro perfis localizados ao norte e sul da area principal de estudo detectaram a assinatura magnetica de varios diques, alguns aflorantes (perfis-norte) mas tambem alguns em subsuperficie (perfis-sul). Estes resultados sugerem que os diques eram rasos e truncados e foram erodidos juntamente com o embasamento cristalino.

The Forensic Geophysical Controlled Research Site of the University of Brasilia, Brazil: Results from Methods GPR and Electrical Resistivity Tomography

In forensic geophysical research, using controlled experiments assists forensic search practitioners in identifying optimal technique(s) and equipment configuration(s) in different burial scenarios. The objective of the research is to observe the geophysical response to different types of buried wrappings, taking into consideration the influence that the presence or absence of a decomposing body (pig carcass) in a lateritic soil in central-western Brazil can have. In this article, the GPR results are presented after a 15day burial period during the rainy season, and the results of Electrical resistivity tomography (ERT) after a burial period of 6 months during the dry season. The controlled site was built in the research area of the University of Brasília, in a region with soil, typical of the Brazilian savannah. 14 simulated clandestine graves of murder victims were constructed, in which seven pig carcasses were wrapped or covered by: soil (backfill), a plastic bag, a bed sheet, cement block, construction debris, a wooden coffin and hydrated lime, respectively a further seven burials, presenting only the wrappings acted as comparison (control burial). During the GPR survey a 400MHz frequency antenna was used. The resistivity surveys were carried out before and after the burial of the targets with dipole-dipole and Wenner-Schlumberger array configurations, with different spacing of electrodes (1.00 and 0.50m). The comparison between the various scenarios with and without pig carcasses revealed that good reflection events occurred mainly due to the wrappings and that pig carcasses attenuated the GPR signal. Electrical resistivity results showed that the Wenner-Schlumberger array presents a better resolution of the lateral boundaries of the burials, and the dipole-dipole array presents a better sensitivity to heterogeneity of the buried materials. The burials with the pig carcasses wrapped in the various materials presented better resistivity contrasts as opposed to the control burials.

GPR APPLIED TO RIGID PAVEMENT FROM SANTOS DUMONT AIRPORT, RJ

ABSTRACT. This paper presents the results of a research performed by using Ground Penetration Radar (GPR) to evaluate the structure of the rigid pavement ofSantos Dumont Airport in Rio de Janeiro, Brazil. The GPR data profiles were acquired with 250 and 700 MHz shielded antennas. The geophysical investigation wasperformed along of 6 profiles, totaling 1432 meters of GPR sections. For calibration of the speed of propagation of electromagnetic wave were drilled three boreholesuntil the depth of 1.8 m. The results of GPR allowed the precise delineation of reflectors related to geotechnical interfaces (pavement thickness – concrete slab andmacadam) and geological (sand/embankment soil), showing the efficiency of this method in this case study. Keywords : GPR, concrete, rigid pavement, Santos Dumont Airport. RESUMO. Este trabalho apresenta o resultado de uma pesquisa desenvolvida usando Ground Penetrating Radar (GPR) para avaliar a estrutura do pavimento rigido do patio de manobras de aeronaves do Aeroporto Santos Dumont, no Rio de Janeiro, Brasil. Para isso foram usadas antenas blindadas com frequencias de250MHz e de 700 MHz. Os dados de GPR foram adquiridos no modo common offset , ao longo de 6 perfis que totalizam 1432 metros de investigacao. Para a calibracao da velocidade de propagacao da onda eletromagnetica foram executados tres furos de sondagem ate a profundidade de 1,8 m. Os resultados de GPR possibilitaram odelineamento preciso de refletores relacionados a interfaces geotecnicas (espessura do pavimento – revestimento de concreto e do macadame) e geologicas (areia/aterrocom entulho), mostrando a eficiencia da aplicacao deste metodo neste estudo de caso. Palavras-chave: GPR, concreto, pavimento rigido, Aeroporto Santos Dumont.

Mapeamento tridimensional de pluma de contaminação através de resistividade elétrica

This work aims at the detection of the contamination caused by a waste disposal area, by the electrical geophysic method of resistivity. Field measurements had been carried out in Mococa, Sao Paulo, Brazil, in a deactivated waste disposal area. The obtained data had been dealt with appropriate softwares that enabled the distinction of the anomalies which help the characterization of the environmental pollution problem. Introducao O objetivo deste trabalho foi delinear a pluma de contaminacao gerada por um lixao desativado, e servir como suporte no Projeto de Recuperacao do mesmo. O local de estudo possui uma area de aproximadamente 150.000 m 2 . A area de estudo localiza-se no municipio de Mococa-SP. Para alcancar este objetivo foi utilizada a metodologia geofisica de eletrorresistividade, com arranjo dipolodipolo com 5 niveis de investigacao e abertura entre eletrodos de 10 metros. Foram adquiridas 6 linhas distribuidas pela area, orientadas perpendicularmente ao local de disposicao de residuos. Para visualizar a dispersao da pluma de contaminacao foi elaborado um mapa tridimensional de

GPR utilizado na deteção da geometria de cavas usadas para disposição de resíduos de óleos lubrificantes

A variety of environmental problems occurs due to the inadequate disposition of residues. Applied geophysics methodologies to environmental studies show great results in the investigation of contaminating. GPR is a practical and fast geophysical method in such investigations, because the electromagnetic signal assists in the delimitation of the contaminating, addressing direct techniques of investigation (boreholes and wells). This study was developed in an old disposition area to residues lubricants oils (dense nonaqueous phase liquids - DNAPL) in the municipal district of Ribeirao Preto, Sao Paulo State. This area is situated in the geological domains of the basaltic floods of the Serra Geral Formation and sandstones of the Botucatu Formation. GPR acquisition was carried out inside and next to 4 ditches of residues disposition, with 100 MHz unshielded antennas, enabling a maximum investigation depth of 7 meters. The limits and of the ditches base can be identify in the GPR sections, except in the ditch 1, which the base is not delineated by GPR. The results show that GPR signal is much attenuated below ditches. This fact could be result of a bacteriological activity in the residue or increase of dissolved salts in the soil caused by acid pH of the residue.