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7th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Oct 2001 - 31 Oct 2001
- Location: Salvador, Bahia, Brazil
- Published: 28 October 2001
101 - 120 of 465 results
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Estudio De Los Acuíferos De La Zona De Arrecifes (Pcia. De Bs. As., Argentina) Mediante Sondeos Eléctricos Verticales
Authors Claudia M. Sainato, B.N. Losinno, A.M. Landini, M.C. Pomposiello and H. MallevilleThe aquifers of the northern zone of Buenos Aires
Province (Argentina) were generally studied through
well data, at a regional scale. However, it is necessary
to know their features at each basin, particularly for
agricultural purposes. Well data are very limited and
geophysical surveys are very scarce.
We previously carried out some vertical electrical
soundings (VES) at the Pergamino zone and in this
work the survey was continued with eight more
soundings at the Arrecifes area. Great differences
were encountered, mainly in the depth of the top of
the salty aquifer, a limiting factor for a drilling project.
Models obtained from VES showed an interface
fresh-salty water which deepens towards the SE
along the Pergamino rivulet, also having a greater
depth at the left margin. Results were compared with
conductivity of water samples and well data. It was
concluded that there is a deterioration of water quality
below 50 m depth at Pergamino zone and below 100
m near Arrecifes.
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Geophysical Studies Of Groundwater Contamination In Ile-Ife Area, Southwestern Nigeria
Authors Adekunle. A. Adepelumi, D. Ako and Taiye R. AjayiHydrogeophysical studies were carried out at the
sewage-disposal site of OAU campus, Ile-Ife, Nigeria.
The objective of the survey was to determine the
reliability of the electrical-resistivity method in mapping
pollution plumes in a bedrock environment. Fifty
stations were occupied with the ABEM SAS 300C
Terrameter using the Wenner array. The electricalresistivity
data were interpreted by a computer- iteration
technique. Water samples were collected at a depth of
5.0 m in 20 test pits and analyzed for quality. The
concentrations of Cr, Cd, Pb, Zn, and Cu are moderately
above the World Health Organisation recommended
guidelines. Plumes of contaminated water issuing from
the sewage ponds were delineated. The geoelectric
sections reveal four subsurface layers comprising
lateritic clay, clayey sand/sand, and weathered/fractured
bedrock, and fresh bedrock. Layers 3 and 4 constitute
the main aquifer, which has a thickness of 3.1-67.1 m.
The distribution of the elements in the sewage effluent
confirms a hydrological communication between the
disposal ponds and groundwater. The groundwater is
contaminated, as shown by sampling and the
geophysical results. Thus, the results demonstrate the
reliability of the direct-current electrical-resistivity
geophysical method in sensing and mapping pollution
plumes in a crystalline bedrock environment.
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Induced Polarization Measurement As A Complimentary Means To Evaluate Aquifer Transport Properties
Authors Sri Niwas, O.A.L. de Lima and Ben ClennellThis paper briefly reviews the current state of the
art in time domain and frequency domain Induced
Polarization measurements for aquifer evaluation,
with special reference to shaly sandstone aquifers.
We provide mathematical foundation to some of
the empirical observations described in this
respect. Then, the general conceptual aquifer
model proposed earlier for shaly granular aquifer,
is extended to Induced Polarization as a possible
means for fast estimation of the aquifer hydraulic
conductivity, complimentary to the values
estimated from resistivity data.
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Integração De Métodos Geofísicos (Er, Em-34, Vlf) E Dados Geológicos Aplicados À Pesquisa De Água Subterrânea Em Terrenos Cristalinos Da Região Do Fumo (Irauçuba), Estado Do Ceará, Nordeste Do Brasil
The aim of this paper is to present an integrated
geophysical study (ER,EM,VLF) with field structural
geology and the interpretation of aerial photographs
applied in the region of Fumo, Irauçuba municipality,
NW State of Ceará, Brazil. This area is characterized
by scarcity on hydrogeological resources. It was
identified an anomalous tubular well for the area,
presenting a production of 8m3/h, greater than the
average production for the crystalline aquifer that is
around 1,7m3/h. The results around the well show the
perfect adaptation of the adopted techniques showing
important anomalies in all the geophysical sensor
used in the area, justifying that the well was placed in
a conductive zone.
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Investigações Geofísicas Em Rochas Graníticas No Município De Itu, São Paulo – Brasil
Authors Jorge Luís Porsani, Francisco Yukio Hiodo and Vagner Roberto ElisGeophysical investigations was realized on the
Granitic Suite of Itu, located near to Itu City, State of
São Paulo - Brazil, with the objective to find fractures
zones in granitic rocks and determine the depth of top
of fresh rock, through of integration of GPR - Ground
Penetrating Radar and Resistivity Methods. The
geophysical profiles were realized on a same line for
a comparative study between these two
methodologies, inside of philosophy of integrated
interpretation. One GPR profile of 80m was acquired
with 50, 100 and 200MHz antennas and two electric
profiles with dipole of 2 and 10m. Analysis of
geophysical profiles allowed to identify two strong
dip reflectors: one about 10m depth, interpreted as
fractures filled with water and the other between 12
and 17m depth that correspond to one resistive region
dipping after of 15m depth, interpreted as the top of
granitic fresh rock. Besides, two anomalous regions
were identified: one about 50m and the other about
80m. In GPR profiles, these regions are characterized
for one shadow zone, because the high attenuation of
electromagnetic waves. In electric profiles, these
regions correspond to the conductive regions that can
be related with the presence of one sub-vertical fracture zone.
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Laboratory Methods For Relating Electrical And Hydraulic Properties Of Shaly Sandstones: Example Of The Sherwood Sandstone Aquifer (Triassic, England)
Authors M. Ben Clennell and Olivar A.L. de LimaWe highlight recent developments in laboratory electrical
properties methods in the domains of time and
frequency, with particular attention to quality control.
We present data from Sherwood Sandstone (Triassic,
England), an important shaly sand aquifer.
Electrical Impedance Spectra (EIS) were
collected over the range 1 mHz to 1 MHz, for nominally
fresh water (conductivity 0.02 S/m), 0.1 M
NaCl brine (0.98 S/m) and 1.0 M brine (7.6 S/m).
Dispersion of real and imaginary parts of the rock
conductivity reveal significant low frequency polarizations.
Induced polarization data in the time domain
using stepped pulses in current and in potential yield
d.c. resistivity, capacitance and integrated chargeability.
Polarization / chargeability is confirmed to be
much stronger in fresh water, decreasing markedly
with salinity. We compare the response of 2 electrode
and 4 electrode methods, and identify pitfalls that can
arise from incorrect sample and electrode preparation.
Permeability measurements made at constant
flow rate and with a constant head show that hydraulic
conductivity decreases over time, by up to one
order of magnitude. We ascribe this to structural
changes in the clays. These time-dependent effects,
which are quite typical of shaly sands, obscure any
simple relationship between permeability and salinity.
Finally, we report some preliminary data on streaming
potential measurements acquired while the 0.1 M
NaCl brine was passed though the sample.
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Mathematical Modeling And Simulation Of Electrical Current Density Distributions In Porous Aquifer Settings
Authors O.A.L. de Lima, H.K. Sato and Sri NiwasWe are presenting in this paper the relative distributions
of horizontal and vertical components of current
density in a vertical section of synthetic aquifer
simulating different geoelectrical settings. These
computations are made using a recently derived general
equation for potential field due to a direct current
source arbitrarily located in a non-uniform layered
medium. On the basis of comparative analysis of
computed data we conclude that in case of fresh water
saturation, the horizontal current density within the
aquifer is greater than the vertical component, for a
substratum of resistive nature, and vice-versa for a
substratum of conductive nature.
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Medidas Elétricas Na Ilha De Algodoal, Estado Do Pará
More LessOs moradores da Vila de Algodoal, localizada na Ilha
de Algodoal, no nordeste do Estado do Pará, têm
experimentado problemas para a obtenção de água
doce, devido, neste ambiente de ilha oceânica, a
cunha salina da água do mar contaminar os poços que
são escavados para a retirada de água do primeiro
lençol subterrâneo.
No presente estudo, tentou-se delimitar a
interface que separa a água doce da água salgada, a
fim de orientar a profundidade máxima a ser escavada
na construção de poços. O estudo foi desenvolvido
usando-se os métodos da eletrorresistividade (SEV e
Caminhamentos Elétricos) e potencial espontâneo.
Foram também tomadas medidas da condutividade
elétrica da água de poços usados no abastecimento
doméstico da Vila.
Os resultados obtidos sugerem uma zona
alongada na direção NW-SE, localizada na porção
central da área investigada, como a melhor região
para locação de poços e a profundidade máxima de 6
m para sua escavação.
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Propagation Of Hydraulic Disturbances Along Fault Systems In The Region Of Caldas Novas (Go)
Authors Luiz E.T. Ferreira and Valiya M. HamzaPropagation of thermo-hydraulic disturbances along
large-scale fault systems in the region of Caldas Novas
(GO) has been studied using analytical and numerical
methods. A finite difference scheme was used
for two-dimensional mapping of hydraulic disturbances
in heterogeneous media that takes into consideration
channeling effects of the existing fault systems.
The results obtained indicate that, under favorable
permeability conditions, infiltration of cold surface
water may take place preferentially along the SE
– NW trending fault systems that run between the
area of impounded surface water and the main zone
of thermal springs. Estimated times for penetration of
the ‘cold front’ may reach values of several tens of
years, depending on the permeability distribution of
the flow paths. A major source of uncertainty in
model calculations arises from the limited knowledge
of the degree of interconnectivity of the fault systems
in subsurface layers. Model results indicate that the
presence of surface water reservoirs close to areas of
large-scale extraction of thermal resources may increase
the potential risk of infiltration and cooling.
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Prospeçãode Á Gua Subterrânea No Karst Do Norte De Minas Gerais, Usando Osm Todos Geof Sicos Vlf E Resistividade D.C. Umcaso Histórico
Authors Ruy Bruno Bacelar de Oliveira and Ernesto C. BacelarGeophysical methods can be helpful in mapping
potential areas of groundwater. Eletrical resistivity and
very low-frequency electromagnetic induction (VLF)
surveys were carried out at a site in the state of Minas
Gerais. The electrical resistivity and VLF data correlate
well, and vertical cross-sections generated from these
data helped map cavities in limestones.
The results of a improved technique to interpret
VLFdata are presented.
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Reavaliação De Poços Revestidos Para Água Subterrânea
Authors Darlindo M.P. Veloso F. and André AndradeUm dos objetivos na captação de água subterrânea é a produção de água de qualidade para o consumo humano. Muitas vezes nos reservatórios há ocorrência de substâncias, como o sal e o ferro, que contaminam o poço, impossibilitando a sua utilização, sendo assim este trabalho apresenta uma nova abordagem para as ferramentas de potencial espontâneo (SP) e resistência (RE), que identifica com clareza a localização do filtro, a posição do nível d’água do poço e a ocorrência de um aquífero de boa qualidade em um poço contaminado. Com essa nova abordagem estas ferramentas, poderão no futuro ser empregada para a reavaliação dos poços inativos com água contaminada com sal ou ferro. A avaliação desta metodologia foi realizada em um poço localizado na região metropolitana de Belém.
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Recent Developments In Groundwater Geophysics
By Ron BarkerGeophysical survey techniques have developed
rapidly over the past ten to twenty years. Although
many might think that we use the same old
techniques – gravity, magnetic, seismic and
resistivity – recent advances in electronics and
computing have resulted in significant changes in the
way we collect and process geophysical data. Table
1 summarises the changes we have seen in the many
geophysical techniques available to us for use in
groundwater investigations.
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Rn222 E Ra226 Em Águas Subterrâneas No Estado Da Bahia
More LessThe 222Rn and 226Ra concentrations in groundwater
from three regions in the State of Bahia with different
geological characteristics was measured. 15 samples
were collected from wells open in the Sedimentary
Basin of Recôncavo in the region of the
Petrochemical Complex of Camaçari, 25 samples
from wells in the cristaline basement in the Ipirá
County and 9 samples from the region of the
uraniferous complex of Lagoa Real. The activity
concentration measured for 222Rn averaged 7.2 Bq/l
(varying from 3.5 to 13.4 Bq/l) in Camaçari, 74.1
Bq/l (varying from 16.1 to 200.9 Bq/l) in Ipirá and
580.3 Bq/l (varying from 41.3 to 3330.5 Bq/l) in
Lagoa Real. For 226Ra, only two samples from
Camaçari presented detectable activity concentration
of 0.06 and 0.10 Bq/l, in Ipirá twelve samples had
activities above the limiar of detection varying from
0.08 to 0.69 Bq/l, and in Lagoa Real four samples had
detectable activities varying from 0.26 to 1.00 Bq/l.
In Ipirá and Lagoa Real was measured activity
concentrations well above the limits for potability
stablished by the american environmental protection
agency of 11.11 Bq/l (300 pCi/l) for 222Rn and 0.11
Bq/l (3 pCi/l) for 226Ra.
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Técnicas Nucleares Usadas Na Localização De Zonas De Fraturas Nos Granitos De Itu-Sp
Authors Francisco Yukio Hiodo, Jorge Luís Porsani and Vagner Roberto ElisNowadays there are many geophysical techniques of
rock fractures mapping as GPR, electromagnetic and
dipole-dipole geoectrical sounding. These methods
don’t give information about the content of fracture
zone, that can be fullfilled of clay. Using nuclear
methods as gamma spectrometry and radon
emanometry become possible to identify the nature
of mineral composition of fracture material and to
study the freshwater circulation using the radon
transport by water. In this work the integration of
nuclear, GPR and geoelectric techniques in Itu
granitic intrusives became very interesting because it
was possible to find and identify fracture in granitic
rock with clay and freshwater content.
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Aeromagnetic Evidence Of The Jurassic Rifting In The Northwestern Chubut Province, Argentina
Authors Carlos J. Chernicoff, Nora Cabaleri and Flavia M. SalaniThe Jurassic sedimentary and volcanic sequence (Cañadón Asfalto Formation) of the northwestern Chubut province was started by an extensional regime. The precise location and geometry of a segment of the Jurassic rift, located in the Cerro Condor area, is distinguished as a narrow, north-south trending magnetic high rendered by the magnetiterich basalts that lie at the base of the sedimentary sequence, which, in turn, are displaced by east-west wrench faults evidenced by cross magnetic lineaments.
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Aeromagnetometric Data Processing Revealing Emplacement History Of Granite Complexes: Lavras Do Sul Intrusive Complex And Jaguari Granite Intrusion Study Case (Rs, Brazil)
More LessThe Lavras do Sul Intrusive Complex (LSIC) is a
shoshonite- to alkaline type intrusion, while Jaguari
Granite Intrusion (JGI) shows just alkaline terms.
These both intrusions are close together in western
part of Sul-riograndense Shield. The aeromagnetic
data processing revealed two types of lineaments
around both intrusions (LSIC and JGI): i) regional
lineaments and ii) intrusion related lineaments; both
lineament types represent different shallow magnetic
source. Regional magnetic lineaments are related to
regional lithologies and deformational structures.
Intrusion related lineaments show a circular
distribution around both LSIC and JGI; they represent
shallow source, positive magnetic anomalies that are
caused by different types of mafic dikes: basaltic,
lamprophyric and/or kersantitic ones. There are also
felsic dikes around both LSIC and JGI, but they are
controlled by radial fracture system. As both LSIC
and JGI are circumscribed by circular dikes, at some
time during the magmatic event, they must have
evolved as a single magma chamber. Circular and
radial dikes also point to a large caldera structure that
must have evolved by multiple collapse episodes. The
development of a caldera structure is compatible to a
ballooning type emplacement mechanism for LSIC and JGI.
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Application Of Airborne Gamma-Ray Spectrometry In Granitic Intrusions Map-Ping: In The Western Of Sul-Riograndense Shield (Rs, Brasil)
Authors Debora Grala Roldão and Adelir José StriederAirborne gamma-ray spectrometry is a geophysical
method very important in the geological mapping,
because it is able to measure the chemical variation
of radioactive elements (K, Th and U). This
information can contribute significantly to an
analysis and to an individualization of granitics
intrusions. In this case, it was applied to granitic
intrusions in the western part of Sul-riograndense
Shield. The analysis of these geochemical
informations derived from the gamma-ray
spectrometry data permitted the discrimination of
eight granitic intrusions (CSGC, SSGC, LSIC and
Passo da Areia, Jaguari, Cerro das Marcas, Saibro
and Passo das Chácaras granites). Granitic intrusions
discriminated in airbone gamma-ray spectrometry
maps displayed a compositional variation (tonal
variation in K, U, Th and ternary maps). Tonal
variation enabled the characterization of granitics
bodies into calcium-alkaline, shoshonitic and alkaline granites.
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Comparação Entre Granitóides De Parte Da Serra Do Mar No Estado Do Paraná Através Da Aerogamaespectrometria
This paper make use of gamma-ray spectometric data
to compare two geological unities with granitoid
composition from Serra do Mar Suite and Paranaguá
Domain, southeast of Paraná state. This rocks
presents different evolution during late Proterozoic.
The obtained results shows that the images of eTh, K
and eTh/eU ratio and the parameter F=K*eTh/eU,
correspond to gechemical indicator of magmatic
differentiation, alcalinity and a avaliation of the
radionuclides mobility on the terrain, which permit
show the differences between the mentioned rocks.
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Deformación Del Mioceno En La Región Del Sur–Este De México
More LessEl estudio consistió en delimitar estructuras en la
litosfera del Sur - este de México, con base en la
interpretación de las cartas de anomalías gravimétricas,
la de interfaz corteza manto, la de los gradientes
horizontales y la de distribución de la sísmicidad y
mecanismos focales para hacer una comparación con
estructuras reconocidas en superficie.
Con estos estudios se deduce que algunas estructuras
superficiales que afectan a las cuencas del Sur - este
se profundizan y están ligadas con la deformación de
estas cuencas sedimentarias Terciarias.
Se propone un modelo de deformación donde hay
una ruptura de la placa continental y la de Cocos
afines del Oligoceno provocando la deformación de
las cuencas terciarias y el volcanismo de los Tuxtlas.
Esta interpretación complementaría ayuda al entendimiento
de los modelos de evolución global propuesta
por varios autores para la evolución del SE de México.
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Estudos Geofísicos No Contexto Geológico Estrutural Da Faixa Apiaí No Sudoeste De São Paulo, Brasil
Authors M.J.T. Rosales, W. Shukowsky and M.S.M. MantovaniA Faixa Apiaí (Sistema de Dobramentos Apiaí) ocupa
a região centro-oeste e norte do Escudo Atlântico no
Paraná ingressando no extremo SW deste escudo em
São Paulo, sendo constituída por complexas
associações metasedimentares subordinadamente
metavulcânicas, estruturadas como nappes com
transporte tectônico para SW, afetadas por intrusões
batolíticas de granitóides diversos (Batólitos
Cunhaporanga, Três Córregos e Agudos Grandes) e
de stocks graníticos, e localmente cobertas por
depósitos molássicos (e. g., Formação Camarinha e
Grupo Castro), sendo o conjunto seccionado por
grandes falhas transcorrentes dextrais de direções
próximas a NE–SW, destacando-se o Lineamento Lancinha.
O presente trabalho trata sobre a aplicação do método
gravimétrico visando complementar o mapeamento
geológico existente da porção sudeste do Cinturão
Ribeira, definida por Faixa Apiaí, e nesta direção
tentar integrar os resultados da interpretação dos
dados gravimétricos num contexto geológicotectónico-
estrutural com o intuito de obter uma visão
detalhada e esclarecedora da estruturação geológica
profunda da região, compreendida aproximadamente
entre as latitudes 23º 30' S - 25º 30' S e as longitudes
50º 00 W - 47º 30' W.
Os resultados obtidos conforme a interpretação dos
dados gravimétricos, permitiram correlacionar
contatos ou falhas verificadas no campo com o
comportamento da anomalia Bouguer, assim como
revelar zonas de importantes descontinuidades
crustais tais como o Lineamento Lancinha, a Falha
Morretes e o Alinhamento Guapiara.
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