Full 3-D inversion of electromagnetic data on PC

Finding Hidden Geothermal Resources in the Basin and Range Using Electrical Survey Techniques: A Computational Feasibility Study

“…For a uniform flat earth, the phase angle is independent of frequency and equal to 45° -substantial departures from this value are diagnostic of large gradients in underground electrical resistivity. The STAR "MT resistivity" postprocessor (described in Chapter 15 of Pritchett, 2002) uses a computational kernel developed by Wannamaker (2001) based on algorithms devised by Sasaki (1999;. Figure 7.1 shows results from the STAR "MT postprocessor" when applied to a onedimensional flat earth (with the resistivity-depth structure illustrated previously for "undisturbed" regions in Figure 2.12) for frequencies between 0.01 and 100 Hz.…”

3D inversion of ZTEM data for uranium exploration

“…One unique feature of the tipper is that the presence of lateral resistivity variations gives rise to an anomalous response (or vertical field), while 1D layered structures produce no response (Labson et al, 1985). The forward modelling of the tipper is based upon a 3D MT modelling algorithm that employs a staggered-grid finite-difference method (Sasaki, 2001). We modified it so that the vertical magnetic fields in the air can be computed.…”

The 3D joint inversion of MT and ZTEM data

“…For the modelling of MT and ZTEM data, plane wave excitation is assumed, and algorithms developed originally for the 2D and 3D modelling of MT data (Farquharson et al, 2002;Wannamaker et al, 1987;Sasaki, 2001) have since been modified to allow for the modelling of ZTEM data (Legault et al, 2012;Sattel and Witherly, 2012;Holtham and Oldenburg, 2010a;Sasaki et al, 2013). Some of these algorithms now allow for the joint inversion of MT and ZTEM data (Wannamaker and Legault, 2014;Holtham and Oldenburg, 2010b).…”