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INDUCED POLARIZATION (IP)

What is Induced Polarization and how do we measure it?

Induced Polarization (PI) is measured by the method that records voltage variations over time or frequency (Telford et al., 1990). This method involves interrupting an electric current in the ground, and the voltage between the M and N electrodes does not immediately return to zero after the interruption.

During this return to zero, charges may concentrate in different parts of the subsurface, returning to their original position while the voltmeter indicates a weak signal.

For a few seconds or minutes (depending on the geology), a fraction of the initial voltage remains in the ground while the charge concentrations dissipate, at which point we measure the induced polarization.

The parameter used for this measurement is the Apparent Chargeability (Ma), expressed in millivolts/volts (mV/V) in the frequency domain and in milliseconds (ms) in the time domain.

Main Applications of Induced Polarization

Induced Polarization (IP) stands out mainly in geophysical acquisition for prospecting metallic minerals. It is commonly combined with electroresistivity: after measuring resistivity, the electric current is interrupted to measure the induced polarization.

These two methods allow the geophysicist to interpret the geophysical profile using resistivity and chargeability data. This approach reduces the chance of geophysical ambiguity, where different materials may respond in a similar way to a physical property.

For example, in an area with two saturated conductive materials, which may have similar resistivity responses, chargeability may offer more defined contrasts, allowing for better distinction between them.

If you want to hire electroresistivity and/or induced polarization (IP) services, contact us and request a free quote!

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