# Dictionary:Magnetotelluric (MT) method

(mag nēd’ ō t∂ loo, rik) A method in which orthogonal components of the horizontal and magnetic fields induced by natural primary sources are measured simultaneously as functions of frequency. Apparent resistivity as a function of frequency is calculated:

Also, , where *Z* is the *Cagniard impedance* or *tensor impedance* (q.v.); see Vozoff (1972)^{[1]}.

Resistivity as a function of depth can be calculated for a layered Earth. For a nonlayered Earth, two apparent resistivity curves result from rotating the MT tensor impedance and interpretation is more involved (see *tensor magnetotelluric method*). The predominant sources of energy for magnetotelluric measurements are micropulsations having frequencies of less than 1 Hz. Sometimes magnetotelluric measurements are made at audio frequencies using energy from sferics; the method is then referred to as the **audiomagnetotelluric method (AMT)**. See *telluric current method.*

## References

- ↑ Vozoff, Keeva (1972). "The magnetotelluric method in the exploration of sedimentary basins".
*GEOPHYSICS***37**(1): 98–141. doi:10.1190/1.1440255.PDF version