Electromagnetic (EM) Surveys in Geophysics

 Electromagnetic (EM) surveys are a powerful geophysical tool used to investigate the Earth's subsurface by measuring variations in its electrical conductivity and magnetic permeability. EM methods are particularly effective for identifying and characterizing different types of subsurface materials, including fluids, minerals, and rock formations.

EM surveys work by generating an electromagnetic field at the surface and then measuring the response from the subsurface. This response varies depending on the conductivity and magnetic properties of the underground materials. For instance, conductive materials such as water-saturated rocks, clays, or metallic ores produce strong EM responses, while resistive materials like dry rocks or hydrocarbons generate weaker signals.

There are various types of EM methods, including controlled-source electromagnetic (CSEM), magnetotellurics (MT), and time-domain EM (TDEM). Each method is suited for different depths and resolutions, making EM surveys versatile in a range of applications. They are commonly used in mineral exploration, groundwater studies, oil and gas exploration, and environmental assessments. EM surveys are particularly valuable in areas where seismic methods may be less effective, such as in highly conductive or magnetically complex environments.

Overall, EM surveys provide critical insights into subsurface properties and are an essential part of modern geophysical exploration and environmental investigations.