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Exploration Technique: Audio-Magnetotellurics

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Electrical Techniques
Parent Exploration Technique: Magnetotelluric Techniques
Information Provided by Technique
Lithology: Rock composition, mineral and clay content
Stratigraphic/Structural: Detection of permeable pathways, fracture zones, faults
Hydrological: Resistivity influenced by porosity, grain size distribution, permeability, fluid saturation, fluid type and phase state of the pore water
Thermal: Resistivity influenced by temperature
Cost Information
Low-End Estimate (USD): 1,118.26111,826 centUSD
1.118 kUSD
0.00112 MUSD
1.11826e-6 TUSD
/ mile
Median Estimate (USD): 8,900.03890,003 centUSD
8.9 kUSD
0.0089 MUSD
8.90003e-6 TUSD
/ mile
High-End Estimate (USD): 25,000.002,500,000 centUSD
25 kUSD
0.025 MUSD
2.5e-5 TUSD
/ mile
Time Required
Low-End Estimate: 4.56 days0.0125 years
109.44 hours
0.651 weeks
0.15 months
/ 10 mile
Median Estimate: 14.17 days0.0388 years
340.08 hours
2.024 weeks
0.466 months
/ 10 mile
High-End Estimate: 28.12 days0.077 years
674.88 hours
4.017 weeks
0.924 months
/ 10 mile
Additional Info
Cost/Time Dependency: Location, Size, Resolution, Terrain, Weather
Audio-Magnetotellurics (AMT) is a natural source application of a magnetotelluric survey aimed at shallower resistivity imaging and more rapid acquisition time relative to a natural source MT measurement.
Other definitions:Wikipedia Reegle

Audio-magnetotelluric surveys (AMT) utilize a passive, natural source predominantly resulting from equatorial lightning discharge as the signal for the MT measurement. The typical period range for an AMT survey is 0.0001 seconds to 0.1 seconds. AMT soundings image the apparent resistivity of the subsurface at shallower depths than broadband MT surveys, typically a few kilometers into the earth's crust.[1]
Use in Geothermal Exploration
See Electrical Techniques: Use in Geothermal Exploration

Field Procedures
The survey layout and equipment for the AMT stations is largely the same as for a MT survey. The only exceptions might be a smaller induction coils for the high-frequency magnetic measurements and shorter electrode lines, as well as more rapid data acquisition time.[1]
Environmental Mitigation Measures
AMT surveys is a non-invasive geophysical technique. The primary impact is due to access to the stations (4WD, ATV, etc.) and possibly line-cutting required for access to the sites in thick vegetation.

Best Practices
Potential Pitfalls

  1. 1.0 1.1 (Chave and Jones, 2012) "The Magnetotelluric Method"

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