|Earthing Project - PLTMG Jayapura (2017)
Grassberg prospecting (2013)
Gorontalo Prospecting (2010)
Electrical resistivity studies in geophysics may be understood in the context of current flow
through a subsurface medium consisting of layers of materials with different individual
resistivities. For simplicity, all layers are assumed to be horizontal. The resistivity of a
material is a measure of how well the material retards the flow of electrical current.
Resistivities vary tremendously from one material to another. For example, the resistivity of a
good conductor such as copper is on the order of 10^-8 Ohm.m, the resistivity of an
intermediate conductor such as wet topsoil is 10 Ohm.m, and the resistivity of poor
conductors such as sandstone is 10^8 Ohm.m.
Due to this great variation, measuring the resistivity of an unknown material has the potential
for being very useful in identifying that material, given little further information. In field studies,
the resistivity of a material may be combined with reasoning along geologic lines to identify
the materials that constitute the various underground layers.
Resistivity is often first encountered in physics when discussing the resistance of an ideal
cylinder of length L and cross-sectional area Aof uniform composition. The resistivity
appears as the material-specific constant of proportionality in the expression for the total
resistance of the cylinder.
R =V/I, where
V is the potential difference between the ends of the cylinder and
I is the total current flowing through the cylinder.
Edge effects are not considered. The resistivity of the material, an intrinsic property of the
material, is then related to experimentally measured extrinsic parameters by
Induced polarization (IP) is a geophysical imaging technique used to identify the electrical
chargeability of subsurface materials, such as ore. The method is similar to electrical
resistivity tomography, in that an electric current is transmitted into the subsurface through
two electrodes, and voltage is monitored through two other electrodes.
Time domain measurements
Typical transmitted current waveform and potential response for time domain resistivity and
induced polarization measurements. Time domain IP methods measure considers the
resulting voltage following a change in the injected current. The time domain IP potential
response can be evaluated by considering the mean value on the resulting voltage, known
as integral chargeability or by evaluating the spectral information and considering the shape
of the potential response, for example describing it with a Cole-Cole model.
Frequency domain measurements
Frequency domain IP methods use alternating currents (AC) to induce electric charges in the
subsurface, and the apparent resistivity is measured at different AC frequencies.