Concerning Some Causes for the Distortion of Transient Sounding Curves

Abstract

The results of field studies show that occasionally the curves obtained in sounding with a transient magnetic field (the ZS method) are distorted in character. These distortions are most severe in the left-hand segments of the curves, and may substantially increase or decrease the value of ρ_τ computed for small times. In extreme cases, the value for ρ_τ computed for the left-most segment of the transient coupling curve may be negative (this part of the transient is opposite in polarity to the excitation pulse). Examples of such distorted curves are shown in Fig. 1. These distorted curves obviously cannot be matched well with theoretical ZS curves computed for sequences of horizontal layers. In a number of cases it has not been possible to recognize the presence of such distortions merely from the form of the curves (for example, curve ZS-81 in Fig. 2), but such curves differ significantly from the type curves established for a particular area (as for example, curve ZS-84 in Fig. 2), permitting distortions to be recognized.

This paper appeared originally in Prikladnaya Geofizika, No. 41, pp. 86–94 (1965).