INFORMATION-CONTENT OF THE ELECTRIC BIPOLE SOURCE FREQUENCY SOUNDING CURVES IN THE TRANSITION ZONE

Numerical studies indicate that information can be gained about the layering even in the transition zone of the source, down to a considerable depth with a properly planned frequency sounding measuring system. As it has been demonstrated, the high resistivity basement can be revealed even with a source-receiver separation 2-times larger than its depth. Model studies demonstrate that the transformation of the measured field into the so-called effective resistivity - with the use of a set of homogeneous earth responses calculated for several different resistivity values - offers a useful tool in the controlled electric bipole source measurement. Effective resistivity frequency sounding curves in the transition zone also give information about layering, and make additional transformations useful in preliminary interpretation. Effective resistivity sounding curves of arbitrary configuration can be determined from any individual field amplitude and phase, or from quantities derived from them. Therefore they can be applied for single - either electric or magnetic - field component frequency sounding as well.