2-DIMENSIONAL INVERSION OF OKLAHOMA EMAP DATA WITH SMOOTHNESS REGULARIZATION

Two-dimensional inversion has been applied to Electromagnetic Array Pr ofiling (EMAP) data obtained in Oklahoma, USA. Since the data comprise scalar impedances measured along a survey line, a TM-mode inversion w as performed on the original data, under the assumption that the surve y line is perpendicular to the geologic strike. The inversion method a pplied is a linearized least-squares scheme with smoothness regulariza tion. The ''optimum smoothness'' is selected based on a statistical cr iterion, ABIC (Akaike's Bayesian Information Criterion), which is deri ved from Bayesian statistics and the entropy-maximization theorem. Sta rting from a homogeneous earth as an initial guess, the inversion iter atively modifies the model structure until the observations are matche d in a statistical sense and parameter modification becomes almost zer o. The final two-dimensional models generally show a very conductive h ost formation (less than 10 Omega.m) with two large resistive bodies o f approximately 100 Omega.m embedded near the middle of the survey lin e.