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Magnetotelluric methods are passive geophysical surveying techniques that measure naturally occurring electromagnetic fields that pass through Earth. 

These electromagnetic waves are created by lightning storms and the interaction of the sun’s solar activity with Earth’s magnetic field. 

By recording these natural electrical signals, the conductivity structure of the subsurface can be inferred from depths of a few kilometres to hundreds of kilometres, providing insights into the conductivity of Earth’s crust and upper mantle. 

A range of passive MT surveying techniques are used to investigate different depths within Earth. These include:

• Audio Magnetotellurics (AMT): sensitive to conductivity variations from the near surface to a few kilometres’ depth. 
• Broadband Magnetotellurics (BBMT): sensitive to conductivity variations at depths of up to tens of kilometres.
• Long-period Magnetotellurics (LPMT): designed to investigate deeper structures, from tens to hundreds of kilometres below the surface. 

GSWA is currently collecting long-period MT data at 40km intervals across 91����Ƶ as part of the WAMT Project. 

Data availability 

All MT data can be downloaded from MAGIX by searching for “magnetotelluric” under the method tab. Regional surveys conducted by, or in collaboration with, GSWA are listed in the table below.

MT data can also be downloaded from the .