INVERSION OF 3-D DC RESISTIVITY DATA USING AN APPROXIMATE INVERSE MAPPING

We present an iterative algorithm for inverting 3-D pole-pole DC resis tivity data. The algorithm utilizes an AIM (approximate inverse mappin g) formalism and iterative inversions are carried out by performing up dates in both model space (AIM-MS) and data space (AIM-DS) by using an approximate inverse mapping with-an exact forward mapping. In the app roximate inverse mapping, the potential anomaly is expressed as a dept h integral of the logarithmic conductivity perturbation convolved hori zontally with a known kernel. Fourier transforming the data equation d ecouples wavenumber components and the Fourier transform of the conduc tivity anomaly is recovered by performing 1-D linear inversions at eac h wavenumber. Inverse Fourier transforming the 1-D inversion results p roduces the sought conductivity. The AIM methodology avoids the genera tion and inversion of a full 3-D sensitivity matrix and is consequentl y fast and efficient. Only one forward modelling is performed at each iteration. The algorithm is tested with synthetic data and a field dat a set from an epithermal region.