Fig. 2

Examples of sounding curves of apparent resistivity and impedance phase. Solid circles with error bars are observed impedances. Note that the error bars include error floors (see Sect. “3-D electrical resistivity inversion” for details). Solid lines are the responses of the inverted resistivity model and dashed lines are those for the sensitivity test model in which the C-2 anomalous zone (see Fig. 3) was assigned an apparent resistivity of 100 Ω m (see Sect. “Sensitivity test for resistivity anomalies”)