Two-Dimensional Inversion of Papua New Guinea Data Using 'Least-Blocked' Models

Magnetotelluric data obtained from a region of Papua New Guinea have been inverted with the aid of a two-dimensional scheme in which the simplest 'least-blocked' model compatible with the data is sought. The average strike direction for the entire region and for all periods is estimated to be approximately N60W. In the rotated frame skew is small everywhere, but ellipticity values remain quite large at some sites, which raises some uncertainty about the assumption of two-dimensionality. Since the data also indicate the presence of local galvanic distortion, a static shift correction has been applied; both the original (rotated) data and the static-shift corrected data have been used to generate 'least-blocked' models. The final models for the two data sets are found to resemble each other quite closely. Both reveal a descending conductive layer beneath a resistive limestone cover of thickness 0.6-0.8 km on southwestern side of the profile increasing to around 2.1-2.4 km on the northeastern side. The one notable difference is that the descending conductive layer divides into two parts separated by a resistive limestone layer in the model obtained from static-shift corrected data, but not in the other.