Introduction to CSAMT

CSAMT (controlled source audio-frequency magnetotellurics) is a commonly-used, surface-based geophysical method which provides resistivity information of the subsurface. This low-impact, non -intrusive technique has been used extensively by the minerals, geothermal, hydrocarbon, and groundwater exploration industries since 1978 when CSAMT equipment systems first became commercially available.

The CSAMT method involves transmitting a controlled signal at a suite of frequencies into the ground from one location (transmitter site) and measuring the received electric and magnetic fields in the area of interest (receiver site). The ratio of orthogonal, horizontal electric and magnetic field magnitudes (e.g. Ex and Hy) are used to calculate the resistivity structure of the earth.

Calculated resistivity values from CSAMT data relate to geology. Primary factors affecting resistivities include rock or sediment porosity, pore fluids, and the presence of certain mineral assemblages. For hydrological investigations, CSAMT data may provide critical information about geologic structure, lithology, water table trends, and trends in pore fluid salinity or contaminant.