The effect of wave number filtering on synthetic three-dimensional magnetotelluric data

A procedure, referred to as wave-number filtering, is developed that dramatically reduces the undesirable effects of 3-D heterogenetics on some elements of the MT (magnetotelluric) impedance. The wave-number filtering process is evaluated by comparing the filtered and the unfiltered apparent resistivities derived from the MT impedence and the filtered and unfiltered MT impedance phases for a particular 3-D model consisting of a heterogeneous region on the surface of an otherwise homogeneous earth. In all cases, the apparent resistivity derived from unfiltered data leads to substantial error in the inferred conductivity of the basement region, while the apparent resistivity derived from filtered data leads to an accurate interpretation of the basement conductivity. As expected, the effect of wave number filtering on the MT impedance phase is much less dramatic than the effect on the apparent resistivity