2-DIMENSIONAL INVERSION OF PAPUA-NEW-GUINEA MAGNETOTELLURIC DATA WITHSMOOTHNESS REGULARIZATION

Two-dimensional inversion has been applied to magnetotelluric data obt ained for petroleum exploration in Papua New Guinea. For the inversion , an impedance tensor is rotated to the general strike direction of th e area, and TM, TE and determinant impedances are calculated. Distorti on-corrected data are also derived to compare the results with the inv ersion of the original data. The inversion method applied is the linea rized least-squares scheme with smoothness regularization. The optimum smoothness is selected based on a statistical criterion, ABIC, which is derived from Bayesian statistics and the maximum entropy theorem. T he forward calculation is based on the finite-element method. Topograp hy along the survey Line is included in the mesh. The start model is a homogeneous earth, and the final models, obtained by the inversions o f TM data, TM and TE data, and determinant data, are generally consist ent with each other. A surface high-resistivity layer of 100-1,000 Ome ga.m corresponds to Miocene limestone with a thickness of approximatel y 1 km. It is underlain by a thick low-resistivity layer of Mesozoic s edimentary rocks which form oil reservoirs.