Aplicações de Técnicas Geofísicas na Parte Emersa da Baía de Guanabara

Anuário do Instituto de Geociências

关键词: geophysic;    electrical resistivity;    Guanabara Bay;    environment;   

DOI  :  

来源: DOAJ

【 摘 要 】

This paper presents the application of the geophysical techniques on twoinvestigations around of Baía de Guanabara, Rio de Janeiro. The first one was carriedout in the area of the Petroflex, a petrochemical industry, located at Campos Elíseosarea in the bank of the bay and the second one at Ilha do Fundão, one of the islandslocated in Guanabara bay.According to Anjos et al.. (2001) the research at Petroflex area was part of thecompany Social Project: “Conheça seu Manguezal” (Knowing your mangrove). For thisresearch the geophysical survey was applied within the industrial park in order to identifysolid waste contamination (rubber, plastic and metal barrels). The Ground PenetratingRadar (GPR) technique was used with the RAMAC/MALA equipment. The study areaconsists of clay and sands deposited in marine conditions, which are frequently contami-nated by salt water. In general, the GPR results obtained in both media, clay material andsediments saturated with salt water are not satisfactory. However the results obtained in thePetroflex area were good. The stratigraphic sequence in the area is the following, from topto bottom: The first bed is a clay landfill, the second bed is formed by dark marine clay, andthe third bed is composed of fine-grained sand with marine shells. The surveys originatedsections with average depths of 14 m and average velocity of 70 m/µs. The results showedtwo physical discontinuities within the second bed (marine clay), which possibly representa Pleistocene platform exposition, described in the literature as Guanabariana Regression.It was also possible to identify anomalies within the first bed (clay landfill) represented bysignal attenuation, and the others identify waste deposits, where the presence of burieddrums was verified. Such work has demonstrated the success of GPR applicability even toclay soil contaminated by salt water.The Ilha do Fundão where the second investigation took place, according toRocha et al. (1998) is the result of an artificial embankment of a former small archi-pelago, built in the early 1950’s. The aim of this work was to identify, by means of ageoelectric survey, the cores of the original islands. Normally, structures near the sea-coast cannot be detected through geoelectric measurements. This is due to the presenceof salt water in sediments. However, in the Ilha do Fundão case, the high electricconductivity sediments have a lens shaped with small thickness and correspond to theembankments. This circumstance allows the detection of deep layers and resistive nuclei.Results were obtained from vertical electric soundings using Schlumberger configurationwith a maximum aperture (ab/2) of 100 m. The original data was published in Rocha et al.(1998).

【 授权许可】

Unknown