Controlled Source Audio MagnetoTellurics
CSAMT SURVEYS
The Controlled Source Audio-Frequency Magneto Tellurics (CSAMT) technique uses an artificial signal source (typically in the range 0.1Hz to 10 kHz) in addition to the natural MT fields. This provides a stronger and more reliable signal and enables imaging of shallower targets than would otherwise be possible with low frequency natural signals alone.
Applications
- Mineral exploration - detection of massive sulphides, base, precious metals, petroleum, and geothermal resources
- Stratigraphy - Mapping lithology
- Hydrogeology - Searching for sources of groundwater and groundwater contamination
- Geotechnical - Tracing the migration of conductive fluids
Advantages
- Higher-precision and faster measurements than natural source MT
- Great range of depth penetration (20m - 2000m)
- Large lateral resolution
- Fast setup
Equipment
A CSAMT survey is a frequency-domain measurement performed with a IP transmitter able to output a square wave, very similar to the equipment used for a Complex Resistivity survey. Magnitude and phase (both electric and magnetic components) of the signal are measured with a multichannel receiver.
Data Processing & Presentation
Measurement of the change in the electric and magnetic fields over a range of frequencies enables an apparent resistivity sounding curve to be constructed. Apparent resistivity is combined with a measure of the phase difference between the electric and magnetic components. Joint inversion of the data using both phase and apparent resistivity provides a more robust interpretation. Modelled data is normally displayed as apparent resistivity versus depth plot.