Refraction seismic and electromagnetic methods have been applied in a experimental scale in the search for groundwater. The efficacy of both methods was verified with about 1.500 m of shallow refraction profiles for three-dimensional geometric delimitation of a paleo-channel in the natural grass land region of Marajó Island; and with an electromagnetic profile (Slingram technique) to detect lateral contacts of fresh and brackish water. The interpretation of seismic data was done using the time-intercept equations for n dipping layers, and the assistance of the geological control of two wells to circumvent problems due to non-detected layers. A low velocity (0,81 km/s) was obtained for the saturated silt-sand sediments filling the paleo-channel. Since the results lead into a velocity reversal in these sediments, the mapping of paleo-channels by refraction seismic is not advisable, unless using special field techniques (digital recording, up-hole survey, S-wave recording, simultaneous reflection,...). The electromagnetic data were analysed semi-quantitatively through a reduced model designed on the basis of apparent resistivities section. An Argand diagram, plotted with the laboratory data, aids in the determination of conductance in non-consolidated sediments similar to those found in Marajó. The use of electromagnetic methods for the lateral reconnaissance of fresh-brackish water zones is recommended since the high frequency (2640 Hz) quadrature component defines these areas with sufficient precision. The comparison between the results of both methods indicates that only a part of the paleo-channel can be considered an aquifer.
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