The time-domain magnetotelluric response over three-layer earth models

Magnetotelluric data observed in frequency and time domains are expressed as apparent resistivity. the apparent resistivity is a weighted spatial average of the subsurface resistivity distribution. In this paper, we develop analytical expressions to compute the apparent resistivity in the time domain for various three-layer earth models. the present approach to computing the magnetotelluric response in the time domain is found to overcome the problems encountered by the method of images. the magnetotelluric response in the time domain for various three-level models have been computed and shown graphically. the time-domain responses show a characteristic behaviour with a small change in layered parameters (resistivity and thickness of the layers), whereas frequency-domain responses do not show such behaviour. This characteristic behaviour of time-domain magnetotelluric sounding curves will be useful in the qualitative interpretation of field data.