Audio-magnetotelluric soundings method
Audio-magnetotelluric soundings method (AMTS) is based on measurements of remote natural sources (thunderstorms etc.) in the frequency band 0.1-1000 Hz. Electromagnetic wave propagates through the Earth-Ionosphere waveguide and can be discussed as a plane wave on the measurement station, where it penetrates into the ground exciting it and inducing some EM field. The response function of the media - surface impedance (Z) connects both electric and magnetic components of this EM field and provides the information about electric properties of rocks at the measurement site.
Surface impedance can be transformed to frequency dependencies of the apparent resistivity (ra) and impedance phase (jz) – sounding curves. Geo-electric cross-section can be reconstructed after its 1D and 2D inversion in corresponding software, providing the information about borders of layers and their resistivities.
AMTS method, in contrast to TDEM and EM soundings, does not use its own source of electromagnetic field and at the same time, it provides the biggest investigation depth. Using of well-developed data processing and 1D, 2D and 3D inversion software provides better studies of heterogeneous media.
AMT method, area of application:
AMT soundings in the band 0.1-1000 Hz allow us to investigate geological structures from dozens meters to several kilometers. AMT method can be applied for the solution of wide range of geophysical tasks from the study of deep geological structures to searching of mineral resources like sulfide ores, kimberlitic pipes, hydrothermal deposits etc.