Magnetotelluric (MT) surveying

An electromagnetic surveying method used to map subsurface resistivity variations by measuring naturally occurring electric and magnetic fields on the seabed or the Earth’s surface

Low-frequency natural electromagnetic fields are generated by the solar wind as it interacts with the Earth’s magnetic field. Because MT surveys have relatively low resolution but excellent depth penetration, the measurements are used to help interpret regional geology. The MT method is particularly useful in areas where topography, high-impedance volcanic rocks or salt make other geophysical methods difficult. MT data are acquired inherently during electromagnetic surveys when the controlled source is inactive.