High Quality Content by WIKIPEDIA articles! Magnetotellurics (MT) is an electromagnetic geophysical method of imaging the earth`s subsurface by measuring natural variations of electrical and magnetic fields at the Earth`s surface. Investigation depth ranges from 300m below ground by recording higher frequencies down to 10,000m or deeper with long-period soundings. Developed in Russia and France during the 1950s, MT is now an international academic discipline and is used in exploration surveys around the world. Commercial uses include hydrocarbon (oil and gas) exploration, geothermal exploration, mining exploration, as well as hydrocarbon and groundwater monitoring. Research applications include experimentation to further develop the MT technique, long-period deep crustal exploration, and earthquake precursor prediction research.