We present a phenomenon which has not been reported until now. It has been found using two independent methods (controlled-source audiomagnetotelluric (CSAMT) analogue modelling experiments and magnetotelluric (MT) numerical computations) that, in the transition zone between the so-called 'overshooting' and the 'normal' period ranges, the anomalies over thin sheet-like 3D models having a complicated geometry are closely connected to the model pattern. This phenomenon and the corresponding enhanced imaging sensitivity have been detected using several different interpretation parameters, in a very narrow period window, towards the end of the overshooting period range of the corresponding sounding curve. This so-called keyhole period range can be determined using simple two-layer MT and CSAMT relationships. Since the effect is small but measurable, the keyhole images could be used as an additional tool in practical problems where the main objective is the detailed geometry of buried targets.
ASJC Scopus subject areas
- Geochemistry and Petrology