An analytic one-dimensional magnetotelluric inversion scheme

Abstract

An analytic one-dimensional magnetotelluric inversion scheme is described. The main characteristics of this new scheme are its simplicity and its minimal requirements in computer time and storage space. The basic idea of the scheme is that for a given period T only the structure above a certain depth matters. The scheme therefore starts with the shortest periods of the available data set and tries to explain the observed response, specifically the apparent resistivity pa(T) and the phase ϕ(T), in terms of a two-layer structure. Shifting successively to longer periods, discrete new layers are introduced at progressively greater depth. Some stabilizing features simultaneously keep the inversion process from diverging and hold the necessary number of layers to a minimum. The properties of the scheme are analysed by studying its performances when working on synthetic and real field data. The scheme can handle fairly scattered data and is very stable. It has, in fact, never been observed to diverge. Examples are given of how the scheme might be handled in practice, especially regarding the use of the causal dispersion relations with which it is possible to ensure that the model proposed by the inversion scheme will return a response function in agreement with the initial data.