Electromagnetic (EM) methods are widely used in geophysics to study the electrical properties of the subsurface. These methods involve the use of electromagnetic waves that propagate through the subsurface and interact with the electrical conductivity of the rocks and soils.
One of the most common EM methods used in geophysics is the transient electromagnetic (TEM) method, which involves the use of a transmitter to send a pulse of electromagnetic energy into the subsurface. The energy induces electrical currents in the subsurface, which in turn generate a secondary electromagnetic field that is measured by a receiver. The measured signals are then analyzed to determine the electrical conductivity of the subsurface.
Another commonly used EM method is the frequency-domain electromagnetic (FDEM) method, which involves the use of a transmitter that emits a continuous wave at a specific frequency. The electrical currents induced in the subsurface by the electromagnetic energy depend on the frequency of the wave and the electrical conductivity of the subsurface. By varying the frequency of the wave and measuring the amplitude and phase of the secondary electromagnetic field, it is possible to obtain information about the electrical conductivity of the subsurface at different depths.
TDEM works by transmitting a short pulse of electromagnetic energy into the ground using a transmitting coil. The energy induces a secondary electric field in the subsurface, which is detected by a receiving coil. The amplitude and decay rate of the secondary electric field are then recorded and analyzed to provide information on the electrical conductivity and permittivity of the subsurface.
TDEM can provide information on the depth and thickness of subsurface layers, the presence and location of conductive minerals and fluids, and the structure and geometry of geological features, such as faults and bedrock. It is commonly used in mineral exploration, groundwater exploration, and environmental studies.
In mineral exploration, TDEM can be used to map the distribution of conductive minerals, such as sulfides and graphite, and to locate mineral deposits. In groundwater exploration, TDEM can be used to map the distribution of aquifers and to identify areas of potential groundwater contamination. In environmental studies, TDEM can be used to map the distribution of contaminants and to monitor the subsurface hydrology.
EM methods are used in a wide range of geophysical applications, including mineral exploration, groundwater studies, environmental studies, and engineering projects. These methods can provide detailed information about the subsurface structure and properties, which can be used to improve our understanding of geological processes and to guide resource exploration and development. However, interpretation of the data obtained from EM methods requires expertise in both geophysics and geology.