Magnetotellurics (MT) is a natural-source, electromagnetic geophysical method of imaging structures below the earth's surface. Natural variations in the earth's magnetic field induce electric currents (or telluric currents) under the earth's surface. Concurrent measurements of orthogonal components of the electric and magnetic fields allow for the calculation of the impedance tensor, which is complex and frequency-dependent. Using this tensor, it is possible to gain insight into the resistivity structure of the surrounding material.