Geophysical imagery is used for viewing sub-surface structures. There are several branches of geophysical imagery, including electrical resistivity tomography, seismo-electromagnetics, and vertical electrical sounding.
Electrical resistivity tomography is used for determining the electrical resistivity of underground structures. This branch uses electrical resistivity measurements which are made at the surface, or with electrodes inserted into one or more boreholes. It is a field of imagery akin to electrical impedance tomography. The only difference between the two is that electrical impedance tomography uses alternating current while electrical resistivity uses direct current.
Seismo-electromagnetics is the field of study involving electromagnetic phenomena that occurs during seismic events such as earthquakes and volcanoes, as well as the use of magnetotellurics. One of the main purposes of this field is to improve earthquake prediction. Seismo-electromagnetic signals have been recorded over a very large frequency range, from ULF to VHF. Low frequency emissions have been noted as precursors to such phenomenon as volcanic eruptions and earthquakes during measurements of background electromagnetic (EM) radiation. EM waves are low frequency waves. These can travel long distances. In fact, during the Cold War, the Soviet Union and the United States developed the use of the ULF band for use with military submarine telecommunication.
Geophysical imagery equipment is used for mineral exploration, lithology mapping, archaeological site investigation, depth to bedrock determination, groundwater exploration, and earthquake detection, among other uses.
There are many products available to help with geophysical imagery needs. The most common of these are earth resistivity meters. These meters are used in the field of archaeology to determine and map the locations of man-made areas below the earth’s surface. The meters are helpful because building foundations and roads tend to not conduct much electricity, while trenches and ditches do.
Earth resistivity and IP data interpretation software are usually required to view the results from these meters. The software packages are available in both 2D and 3D format.
Using these products, which can be found at many geophysical and IP imaging system websites, can greatly increase the speed with which scientific explorations are carried out. Find products from Advanced Geosciences at www.agiusa.com.