# 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 ${\displaystyle \rho _{a}}$as a function of frequency ${\displaystyle f}$ is calculated:
${\displaystyle \rho _{a}={\frac {1}{\mu \omega }}{\Big (}{\frac {E_{i}}{H_{j}}}{\Big )}^{2},\omega =2\pi f}$
Also, ${\displaystyle \rho _{a}=0.2{\frac {Z^{2}}{f}}}$, where Z is the Cagniard impedance or tensor impedance (q.v.); see Vozoff (1972)[1].