Dr Peter Fullagar

Fullagar Geophysics Pty Ltd, Hobart, Australia

Dr James Reid

Mira Geoscience Ltd, Perth, Australia

Overview
Interpreting geophysical data in terms of rectangular plates or dyke-like slabs is effective in many situations. However, not all targets of interest are tabular and fairly thin. Triaxial ellipsoids are an attractive alternative: geometrically simple (corner-free), mathematically tractable, and able to encompass a diverse continuum of shapes including elongate lenses and equi-dimensional pods as well as planar discs.

The ellipsoid-based program, Parametric, was originally developed for fast modelling and inversion of transient EM data, both dB/dt and B-field. It computes EM resistive and inductive limit responses of ellipsoids using a novel magnetostatic algorithm. Parametric applications have recently been expanded to include magnetometric resistivity (MMR) and potential field (TMI and gravity) data. During inversion the ellipsoid property, location, and shape parameters can be constrained by upper and lower bounds entered by the user.

The purpose of the workshop is to familiarise attendees with the new ellipsoid-based modelling and inversion options. Brief technical introductions will be followed by demonstrations – applying the software to field data using Geoscience Analyst utilities.

Key features of the Parametric approach are itemised below:

TEM features:

  • inverts airborne, ground, and downhole 1-, 2- or 3-component TEM data sets, both dB/dt & B-field
  • inverts data from multiple Tx loops and multiple downhole profiles or survey lines simultaneously
  • ellipsoids can be susceptible as well as conductive
  • suitable for sub-audio magnetic (SAM) “total field” data sets
  • runs “stand-alone” or in conjunction with other software, e.g. starting models (number of ellipsoids and their initial parameter values) can be based on VPem3D inversion results

MMR features:

  • inverts 1-, 2- or 3-component MMR data sets in terms of conductive ellipsoids in a homogeneous host

TMI features:

  • inverts TMI data sets in terms of magnetised ellipsoids
  • ellipsoid magnetisation can be remanent and/or induced
  • inverts remanent magnetisation parameters: declination, inclination, and Q (or effective susceptibility)

Gravity features:

  • inverts gravity data sets in terms of dense ellipsoids

Workshop Timetable (draft)
0. Welcome 8.30 – 8.35

1. Introduction
1.1 Parametric overview 8.35 – 9.15
1.2 Geoscience Analyst utilities overview 9.15 – 9.40

2. Demonstrations
2.1 TEM inversion 9.40 – 10.10
Break 10.10 – 10.30
2.2 MMR inversion 10.30 – 10.55
2.3 TMI inversion 10.55 – 11.20
2.4 Remanent magnetisation inversion 11.20 – 11.45

3. Conclusion
3.1 Review 11.45 – 12.00
3.2 Future developments 12.00 – 12.15
3.3 Discussion 12.15 – 12.30

What are the learning outcomes?
The workshop will provide tutorials on: (i) The theoretical basis underlying the Parametric options. (ii) Running Parametric software to invert TEM, MMR and potential fields data. (iii) Geoscience ANALYST utilities for data pre-processing, model creation, inversion, and review of Parametric modelling results.

Who should attend?
Geophysicists interested in parametric modelling of TEM, potential fields, and MMR data.