Frequency-Domain Electromagnetic Survey
Exploration Technique: Frequency-Domain Electromagnetic Survey
|Exploration Technique Information|
|Exploration Group:||Geophysical Techniques|
|Exploration Sub Group:||Electrical Techniques|
|Parent Exploration Technique:||Electromagnetic Profiling Techniques|
|Information Provided by Technique|
|Lithology:||Detection of high-conductivity bodies in the subsurface.|
|Thermal:||Detection of the presence of a thermal anomaly through its resistivity signature.|
|Low-End Estimate (USD):|| 2,928.38|
292,838 centUSD/ mile
|Median Estimate (USD):|| 4,505.20|
450,520 centUSD/ mile
|High-End Estimate (USD):|| 7,079.60|
707,960 centUSD/ mile
|Low-End Estimate:|| 9.12 days|
0.025 years/ 10 mile
|Median Estimate:|| 16.89 days|
0.0462 years/ 10 mile
|High-End Estimate:|| 27.35 days|
0.0749 years/ 10 mile
|Cost/Time Dependency:||Location, Size, Resolution, Terrain, Weather|
- "Lawrence Berkeley National Laboratory (LBNL) has conducted geothermal exploration projects utilizing frequency-domain electromagnetics. In general, frequency-domain EM tools (such as the Geonics EM-31, EM-38 and EM-34) are suitable for shallow geophysical investigations for mapping soil conductivities and detection of buried conductors. '"`UNIQ--ref-00000000-QINU`"' However, LBNL has applied a prototype frequency-domain EM induction system, the EM-60, to geothermal exploration projects in Nevada with a depth of investigation ranging from 2-5km. '"`UNIQ--ref-00000001-QINU`"'" cannot be used as a page name in this wiki.
- The given value was not understood.
- "Frequency-domain EM tools such as the LBNL EM-60 are able to resolve the depth to conductors which may be associated with thermal anomalies. '"`UNIQ--ref-00000002-QINU`"' Current literature or case studies regarding the application of the EM-60 to geothermal exploration are limited." cannot be used as a page name in this wiki.
- The given value was not understood.
The current applied to the transmitting loop generates a primary magnetic field; this primary magnetic field induces secondary electrical eddy currents in the subsurface according to Faraday’s Law. The eddy currents, in turn, generate a secondary magnetic field which is measured with a three-component magnetometer (see Ground Magnetics) at pre-defined station spacing, depending on the survey design. The terrain resistivity is inversely proportional to the ratio of the primary and secondary magnetic fields when operating at low induction numbers.  The associated maximum depth of investigation for these particular survey parameters is approximately 5 km. 
• The transmitter-receiver separation is approximately equivalent to the maximum depth of exploration; survey design should take this into account. 
• A reference or remote magnetometer can be used in addition to the field measurements as a correction for natural geomagnetic variations. 
- (Geomatrix 2010) "Electromagnetic Equipment"
- (Wilt et al. 2010) "A Comparison of Dipole-Dipole Resistivity and Electromagnetic Induction Sounding over the Panther Canyon Thermal Anomaly, Grass Valley, Nevada"
- (Wilt et al. 1983) "Experience with the EM-60 electromagnetic system for geothermal exploration in Nevada "
- (Morrison 1978) "Description, Field Test and Data Analysis of a Controlled-Source EM System (EM-60) "
- (Wilt et al. n.d.) "An Electromagnetic (EM-60) Survey in the Panther Canyon Area Grass Valley, Nevada "
- (McNeill 1980) "Technical Note TN-6: Electromagnetic Terrain Conductivity Measurement at Low Induction Numbers"
|Page||Area||Activity Start Date||Activity End Date||Reference Material|
|Frequency-Domain Electromagnetics Survey At Kilauea East Rift Geothermal Area (FURUMOTO, 1976)||Kilauea East Rift Geothermal Area||1973||1975|