3-D Interpretation of Magnetotelluric Data in Central Leyte and Northern Negros Geothermal Areas, Central Philippines

Abstract

A stable three-dimensional (3-D) inversion technique of magnetotelluric (MT) data has been developed and applied to the data obtained in two geothermal fields in the Philippines by PNOC-EDC: Central Leyte and Northern Negros geothermal fields. The inversion method is based on the Gauss-Newton (linearized least-squares) method with smoothness regularization. Static shifts are also treated as unknown parameters in the inversion. A Bayesian criterion ABIC is applied to search the optimum trade-off among the minimization of the data misfit, model roughness and static shifts with an assumption of Gaussian distribution in these quantities. Although the data quantity is large and several parts of the data are contaminated by various noises, the inversion of the two datasets has behaved properly and a stable convergence has been attained. The interpretation of the resultant resistivity models has been still primitive, however, the model of the Central Leyte data indicates a good correlation with the geologic trends of the Philippine Fault and the structure of the nearby volcano.