and Nord-West Ltd use onshore MT more than any other oil company in the world, conducting thousands of MT soundings for hydrocarbon exploration and mapping throughout the globe. Mining exploration MT is used for various base metals (e.g. nickel) and precious metals exploration, as well as for kimberlite mapping. INCO's 1991 proof-of-concept study in Sudbury, Ontario, Canada sensed a 1750-meter-deep nickel deposit. Falconbridge followed with a feasibility study in 1996 that accurately located two Ni-Cu mineralized zones at about 800 m and 1350 m depth. Since then, both major and junior mining companies are increasingly using MT and audio-magnetotellurics (AMT) for both brownfields (near known deposits) and greenfields (uncharted land) exploration. Significant MT mapping work has been done on areas of the Canadian Shield. Diamond exploration, by detecting kimberlites, is also a proven application. Geothermal exploration MT geothermal exploration measurements allow detection of resistivity anomalies associated with productive geothermal structures, including faults and the presence of a cap rock, and allow for estimation of geothermal reservoir temperatures at various depths. Dozens of MT geothermal exploration surveys have been completed in Japan and the Philippines since the early 1980s, helping to identify several hundred megawatts of renewable power at places such as the Hatchobaru plant on Kyushu and the Togonang plant on Leyte. Geothermal exploration with MT has also been done in the United States, Iceland, New Zealand, Hungary, China, Ethiopia, Indonesia, Peru, Australia, and India. Other MT is also used for groundwater exploration and mapping research, hydrocarbon reservoir monitoring, deep investigation (100 km) of the electrical properties of the bedrock for high-voltage direct current (HVDC) transmission systems, carbon dioxide sequestration, and other environmental engineering applications (e.g. nuclear blast site monitoring and nuclear waste disposal site monitoring). Research applications Crust and mantle MT has been used to investigate the distribution of silicate melts in the Earth's mantle and crust; large investigations have focused on the continental US (National Science Foundation EarthScope MT Program), the East Pacific Rise, Australia (AusLAMP MT Program), Southern Africa (SAMTEX MT Project), China (Part of the Sinoprobe project) and the Tibetan Plateau. Research work relevant to MT method may include understanding the plate-tectonic processes in the highly complex geological regions such as the collisions of the African and European plates and in orogenic processes in Western Europe such as the Variscan Orogeny and the Caledonian Orogeny Earthquake precursor prediction Fluctuations in the MT signal may be able