= Magnetotelluric sounding
<Magnetotelluric sounding> infers subsurface <electrical resistivity> from naturally varying <electric fields> and <magnetic fields>. Surface electrodes measure potential differences while magnetic sensors record the same fluctuations. In the <frequency domain>, the relation between horizontal field components defines an <electrical impedance> that depends on the conducting structure below the station.
Low <frequencies> generally penetrate farther than high <frequencies>, as expected from the <skin depth> of a conductor. A range of frequencies therefore constrains a range of depths. The inferred <electrical resistivity> depends on connected fluids, composition and <temperature>; a conductive zone does not uniquely identify molten <rock>.<Magnetotellurics by Geoscience Australia>[Method description: field ratios, depth sensitivity and bulk resistivity]{ref}
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