Geophysical Mapping: Method Details
Printer Friendly Version  
26 of 48
Method Name: Magnetotellurics, Controlled source audiomagnetotellurics
Method Type:   Electromagnetic Methods
Assigned Problems:
0 Depth of Overburden-bedrock interface Civil Engineering
0 Host sediments, hydogeological settings Hazardous Waste
   '0' = Application possible/limited use
Principle:   Signals from natural (MT) or artificial (CSAMT) electromagnetic sources, located outside of the investigation area, are employed to determine the gross subsurface resistivity distribution.
Keywords:   Megnetotellurics; MT; Controlled Source Audiomagnetotellurics; CSAMT
  • Target must be characterized by a resistivity contrast
  • Buried wires, metal pipes, metal fences may influence measurements
  • Urban areas may cause high noise levels (e.g. stray currents)
  • Prohibited use in areas around high-voltage power line pylons, railways and antennas
Resolution:   Spatial resolution scales with frequency of the source signal. MT provide a spatial resolution of a few hundreds m to km. CSAMT provide a spatial resolution of a few tens to several hundreds of m. Investigation depths of MT surveys can be up to several tens of km. CSAMT surveys are usually limited to 1 km.
Expected Results:  
  • Measured parameter: electrical- and magnetic fields. Electrical fields are measured with electrodes and magnetic fields are recorded with induction coils. Therefore, both fields are represented by voltages.
  • Data analysis: 1-D, 2-D or 3-D inversion of the data observed
  • Interpretation: association of the resistivities with geological units
Combination with other Methods:  
  • Required additional information: additional geological information may be helpful
  • Related add-on information: vertical electrical sounding; electromagnetic methods
  • Independent additional information: seismic methods; magnetic or gravimetric methods
Operating Expense:  
  • Crew size: 1 key person; 1 - 2 assistants
  • Acquisition speed: 20 - 40 measurements per day. Additionally around 1 day assembly and disassembly of the source (CSAMT)
  • Processing: 1 - 2 days per measuring day
  • Equipment rental costs: low to intermediate
Parameters to specify:  
  • Station spacing (depends on lateral variability of the subsurface structure)
  • Profiles should be perpendicular to strike of geological units
QC Documents:  
  • Calibration tests
  • Around 2 - 5 % of repeated measurements
  • Field notes
  • Resolution matrices
  • 1-D resistivity-depth functions
  • 2-D resistivity distributions along a profile
  • 3-D resistivity models
Printer Friendly Version