Magnétotellurique

The magneto-telluric is a technique of exploration Géophysique based on the variations of resistivity of the basement, using the magnetic field induced by the telluric Courants.

Principle

It is about an electromagnetic method of Prospection where the emission is not controlled. Electric currents, of natural or artificial origin traverse the basement permanently. Their variations induce magnetic fields which can be detected on the surface.

The device of measurement consists of three Magnétomètre S directed according to the vertical and the principal directions of the supposed structure of the basement. At each station one measures during a certain time the fluctuations of the magnetic field in the three directions.

The application of simplifying assumptions (ground punt, homogeneous and isotropic, the current cannot have of vertical component, it does not have there a power source close to measurement, etc) to the Maxwell's equations makes it possible to obtain simple relations between the three measured components, which utilize only the electromagnetic parameters of the basement. These relations can be put in the form of invariants similar to Résistivité S, which can be charted according to the position of the measurement and the frequency of the signal, similar to a depth.

It is then possible to carry out a modeling of the basement to deduce from the cartography of the invariants according to the frequency a cartography of the resistivity according to the depth.

Thetelluric one is used in prospection of surface. It is particularly adapted in the search of metal ores and the study of geothermic sites. Thetelluric one in underwater prospection is a recent extension of magneto-telluric terrestrial and is used as well in basic research as in marine prospection.

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