TITLE:
Electrical Resistivity Tomography and TDEM Applied to Hydrogeological Study in Taubaté Basin, Brazil
AUTHORS:
Rodrigo Corrêa Rangel, Jorge Luís Porsani, Cassiano Antonio Bortolozo, Luiz Rodrigo Hamada
KEYWORDS:
Electrical Resistivity Tomography (ERT), Time Domain Electromagnetic (TDEM), Hydrogeophysics, Taubaté Basin, Brazil
JOURNAL NAME:
International Journal of Geosciences,
Vol.9 No.2,
February
26,
2018
ABSTRACT:
This research applies Electrical Resistivity Tomography (ERT) and Time Domain
Electromagnetic Method (TDEM) to study the hydrogeology of the
Taubaté basin, which is characterized by half-grabens with about 850 m of
maximum sediments thickness. The study area is in Taubaté city, São Paulo
State, Brazil, where the Taubaté aquifer is an important water source. The
Taubaté Group is the main sedimentary package of the basin; it is formed
mainly by shales that form aquicludes, and thin layers of sandstones that form
the aquifer. There are 40 groundwater exploration wells in Taubaté city that
provide important information. The study purpose is to characterize the
geoelectrical stratigraphy of the subsurface to locate the contact between the
Quaternary and Tertiary sediments and to identify the Taubaté aquifer. The
ERT is used for shallow investigations (tens of meters) and the TDEM can
reach a great investigation depth (hundreds of meters). Therefore, these geophysical
methods are complementary. The ERT data were acquired with the
pole-dipole array with 20 m of electrodes spacing and 400 m length, and the
TDEM data with the central-loop array with a 200 × 200 m transmitter loop.
The results permit to define the contact between the Quaternary and Tertiary
sediments around 15 m depth, the Pindamonhangaba Formation between 15
m and 30 m depth and the Taubate Group between 30 m and 300 m depth.
The TDEM method defined the Taubaté Group as a single geoelectric layer
because the shale and the sandstone layers are all very conductive. The basement
is formed by gneiss, which is a very resistive rock. The TDEM method is
not able to identify a high conductor/resistor contrast. Overall, the results are consistent with the known geology and the wells information.