Speaker: Peter Fullagar, Fullagar Geophysics Pty Ltd.
Title: Beyond Plates – fast TEM inversion using conductive ellipsoides
Date: Thursday, May 25, 2023
Time: 4:30pm to 5:30pm PDT
Location: Room 111 – 409 Granville Street, Vancouver, BC, V6C 1T2
Interpreting TEM anomalies in terms of conductive rectangular plates is effective in many situations. However, not all conductors are thin and planar. Triaxial ellipsoid conductors represent an attractive alternative: geometrically simple (corner-free), mathematically tractable at early and late time limits, and able to encompass shapes ranging from poddy to tabular to lensoidal to elongate. Accordingly a fast magnetostatics-based algorithm has been developed to compute ellipsoidal conductor responses in both resistive and inductive limits. Focusing on TEM data close to the resistive or inductive limit is attractive not only because it simplifies both the physics and the computations, but also because in many cases the late time or early time response is of particular interest in mineral exploration. Inversion of measured data entails adjustment of selected ellipsoid parameters, subject to user-imposed upper and lower bounds. The methodology is suitable for downhole, ground, or airborne TEM, either impulse or step response. In this presentation the conductive ellipsoid forward and inverse algorithms are briefly described and illustrated via application to TEM field data.
Peter Fullagar holds a PhD in geophysics from UBC. He has over 40 years experience in base metal and precious metal exploration, and in metalliferous and coal mining geophysics. He worked for a total of 14 years with Western Mining Corporation (WMC) and Rio Tinto in Australia. Peter has also held academic and research positions, at Ecole Polytechnique in Montreal and with CSIRO Exploration & Mining in Brisbane. Since his tenure as Chief Geophysicist for WMC in the early 1990s he has promoted utilisation of geophysics in operating mines. He established Fullagar Geophysics Pty Ltd in Brisbane in 1998 and has consulted privately for the past 25 years. During that time he has developed geophysical modeling and inversion software, mostly for EM, potential fields and borehole logging, with a focus on integrated interpretation of geophysics and geology. He has also supervised several MSc and PhD students, and has taught undergraduate courses in potential fields, and electrical and EM methods, at the University of Queensland. He is currently based in Noosa, Queensland.