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MAGNETOTELLURIC METHOD

Exploring Telluric Currents: Mapping Subsurface Resistivity

The magnetotelluric (MT) method represents a passive and electromagnetic approach to geophysical exploration, operating in the frequency domain. It consists of the simultaneous measurement, on the Earth’s surface, of the natural temporal variations of the magnetic (H) and electric (E) fields in orthogonal directions.

The objective is to map the distribution of electrical resistivity of subsurface structures at depths ranging from a few tens of meters to hundreds of kilometers..

Upon penetrating the ground, electromagnetic fields induce internal currents in the Earth, known as telluric currents, generating secondary magnetic fields. These currents originate from the magnetosphere and ionosphere, assuming that electromagnetic waves reach the Earth’s surface in the form of a flat wave. The theory of electromagnetic induction, along with related formulas, is grounded in various literary sources (Simpson, Bahr, 2005; Castells, 2006).

Applications of the Magnetotelluric Method

In the Brazilian context, the magnetotelluric (TM) method has been predominantly employed in academic studies for structural and tectonic analyses of the Earth’s crust. In recent years, however, there has been a change in focus in the market, with greater application of MT in oil exploration projects, as evidenced by ANP bids for the acquisition of data in sedimentary basins. Despite the growing demand in the mining industry to explore potential mineral resources at depths of up to 1500 meters, the use of MT for this purpose is still limited in Brazil.

After a magnetotelluric data acquisition campaign, the processing steps are carried out, resulting in the following main PRODUCTS:

Pseudosections of resistivity and phase as a function of period in TE, TM and TE+TM modes;
Dimensionality chart using Waldim’s criterion;
2D inverted geoelectric model;
3D inverted geoelectric model;
Geological-geophysical model interpreted.

For the application of the magnetotelluric method, Geoscan has a multidisciplinary team of geophysicists, geologists and engineers. Contact us and request a free quote.

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