magnetotelükrikás

Magnetotellurics, often abbreviated as MT, is a geophysical surveying method used to investigate the Earth's subsurface electrical resistivity structure. It relies on the natural electromagnetic fields generated by lightning storms and other atmospheric phenomena, as well as by currents flowing in the Earth's magnetosphere. These natural time-varying electromagnetic fields penetrate the Earth's crust and induce electrical currents within conductive subsurface layers.

The method involves deploying sensors, typically magnetometers to measure the variations in the Earth's magnetic field and electric field sensors (often dipoles) to measure the variations in the Earth's electric field at the surface. By simultaneously recording both the electric and magnetic field components over a range of frequencies, geophysicists can calculate the apparent resistivity and phase of the subsurface at different depths. Different frequencies are sensitive to different depths of investigation, with lower frequencies probing deeper.

The relationship between the natural electric and magnetic fields, and the Earth's resistivity, is governed by Maxwell's equations. By analyzing the impedance tensor, which relates the horizontal electric and magnetic fields, information about the subsurface conductivity can be deduced. This information is typically presented as 1D, 2D, or 3D resistivity models.

Magnetotellurics is a passive geophysical method, meaning it does not require artificial sources of electromagnetic energy. This makes it suitable for large-scale regional surveys and for investigating areas where active source methods are impractical. MT surveys are widely used in various applications, including mineral and hydrocarbon exploration, geothermal resource assessment, groundwater studies, and crustal investigations. The depth of investigation can range from a few tens of meters to hundreds of kilometers, depending on the frequency band used and the conductivity of the subsurface.