Basic Magnetotellurics by Christopherson

If you like more detail than Wikipedia offers...

"Dissected, the word “magnetotellurics” has two parts – “magneto” for magnetic and “telluric” for earth currents. MT is a geophysical method that measures magnetic and electric fields that are found in the earth. Basically, MT is a geophysical method that measures naturally occurring, time-varying magnetic and electric fields. From these measurements we can derive resistivity estimates of the subsurface, from the very near surface to tens of thousands of feet. "


LINK to Christopherson presentation

Magnetotellurics on Wikipedia

I always find Wikipedia is a good first stop when learning about something new. For a lot of mining and oil & gas people (including geologists!), a couple of pages of non-marketing background is often helpful when trying to figure out onshore EM.


LINK

Magnetotellurics and Mt. St. Helens in New Scientist

MT used to look at magma under Mt. St. Helens:

"Magma can be detected with a technique called magnetotellurics, which builds up a picture of what lies underground by measuring fluctuations in electric and magnetic fields at the surface. The fields fluctuate in response to electric currents travelling below the surface, induced by lightning storms and other phenomena. The currents are stronger when magma is present, since it is a better conductor than solid rock."


Link: http://www.newscientist.com/article/mg20227124.700-supervolcano-may-be-brewing-beneath-mount-st-helens.html