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2D Inversion of Resistivity and IP Data with Topography

Publisher –
Northwest Mining Association, 102nd Annual Convention Proceedings, Geophysics/Geochemistry Session, Spokane, Washington, 1996.

Authors –
Scott MacInnes, Ken Zonge, Zonge Engineering and Research Organization, Tucson, Arizona, USA

Paper – [pdf] MIN_NWMA1996

Abstract
Two-dimensional, smooth-model inversion of resistivity and induced polarization data produces image-like, electrical property sections which improve the data’s interpretability. Recent software improvements enable routine smooth-model inversion of resistivity and induced polarization (IP) data. Nearly uniform starting models are generated by running broad moving-average filters over lines of dipole-dipole or pole-dipole data. Model resistivity and IP properties are then adjusted iteratively until calculated data values match observed values as closely as possible, given constraints which keep the model section smooth. Calculated values are generated with a finite element algorithm which can be adapted for accurate two-dimensional modeling of data collected in rough terrain.

Conclusions
Smooth-model inversion of sample data show the method’s utility as an interpretation aid and the

importance of modeling topography in areas with significant relief. Smooth modeling can be used as an automated imaging tool by generating a priori starting models with a broad moving-average of observed data. It can also be used as tool for interpretive synthesis by basing a priori models on independent geologic information from mapping, drilling or other geophysical surveys.

Topographic effects can distort apparent resistivity data in areas with rough terrain. Using a finite-element, forward-modeling algorithm allows for distorted computational meshes which closely follow irregular topographic profiles and accurately model topographic effects. Smooth-model inversion improves the interpretability of resistivity/IP data and in areas with topographic relief, results are improved further by including topographic modeling in the inversion procedure.