10 Questions
What is a key advantage of EM methods over contacting electrical resistivity surveys?
Faster survey times
What is the main difference between Active and Passive Electromagnetic methods?
The source of the electromagnetic field
What is one of the main applications of electromagnetic methods in terms of resource assessment and exploration?
Mineral resource assessment and exploration
In which type of land model do EM surveys counter survey difficulties?
Models with very conductive uppermost layers
What is the primary factor that affects the level of inquiry in TEM?
Loop size
What is the relationship between the distance between the transmitter and receiver coils and the depth range under investigation in FEM?
Directly proportional
What is the main parameter measured by Electromagnetic and Electric methods?
Electrical conductivity
What is the purpose of Electromagnetic methods?
To measure the electrical conductivity of the Earth's materials
Which of the following is NOT a typical use of electromagnetic methods?
Seismic data acquisition
What are the three types of measurements that can be conducted using Electromagnetic methods?
Mapping, profiling, and sounding
Study Notes
Basic Concepts
- Electromagnetic methods are categorized into two types: Active (controlled source) methods and Passive (natural field) methods.
- Controlled source methods include GBR and MagnetoMetric resistivity, while natural field methods include Magnetotelluric and Telluric Methods.
- Electromagnetic methods can be classified as frequency-domain (FEM) or time-domain (TEM) systems.
- These methods measure the electrical conductivity (resistivity) of the Earth's materials, which is the same measured parameter as Electric methods, but with different measurement methods.
- Electromagnetic methods can be used for land-based and airborne surveys, marine surveys, and borehole logging.
- Surveys can be conducted through three types of measurements: mapping, profiling, and sounding.
- Electromagnetic methods provide information about the variation in conductivity within a certain depth range.
TEM Method
- The level of inquiry is closely correlated with the loop size, recording time interval, and shut-off time in TEM.
- TEM methods have a greater penetrating depth than electric methods.
Advantages
- One of the main advantages of EM methods is that they do not require direct contact with the ground.
- EM surveys can be made faster than equivalent surveys using contacting electrical resistivity.
- EM methods counter some survey difficulties with land models having very conductive uppermost layers.
Uses
- Electromagnetic methods are applicable for:
- Mineral resource assessment and exploration
- Investigating and monitoring hydrocarbon reserves
- Surveys of groundwater
- Mapping contaminant plumes
- Geothermal resource investigations
- Contaminated land mapping
- Landfill surveys
- Finding man-made and natural cavities
- Location of geological faults
- Geological mapping and Permafrost mapping
- UneXploded Ordnance (UXO)
This quiz covers the basics of electromagnetic methods in geophysics, including active and passive methods, and their applications in geology.
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