Summary

Synthetic ZTEM responses computed with 2D and 3D algorithms are compared. Excellent agreement is observed between 2D and 3D responses for structures with long strike lengths. Using the 2D inversion algorithm on synthetic 3D responses indicates artifacts being introduced when limited strike length is present: the conductivity of structures such as resistive hills and conductive structures is underestimated.

Synthetic 3D models of a conductive target in a resistive host are used to demonstrate the effect of target strike length and target conductance on the ZTEM response. With an increase in strike length or conductance, the amplitude of the ZTEM responses increases. However, the amplitudes increase unevenly over the range of ZTEM frequencies. For low-conductance targets with short strike lengths the strongest responses are observed at the highest frequencies, whereas for high-conductance targets with long strike lengths the strongest responses are observed at the lowest frequencies. In the presence of a conductive overburden, responses are reduced by overburden blanking, but they can be boosted by current channeling if the conductor is in contact with the overburden.

2D and 3D inversion results of ZTEM survey data from Forrestania, Western Australia, show good agreement. The derivation of pseudo-profiles allowed for the 2D inversion of across-line data, which resulted in the modeling of structures not mapped by the in-line data.

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