Exploration geophysics

Exploration geophysics is an applied branch of geophysics and economic geology, which uses physical methods at the surface of the Earth, such as seismic, gravitational, magnetic, electrical and electromagnetic, to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs. It can also be used to detect the presence of unexploded ordnance. Exploration geophysics can be used to directly detect the target style of mineralization by measuring its physical properties directly. For example, one may measure the density contrasts between the dense iron ore and the lighter silicate host rock, or one may measure the electrical conductivity contrast between conductive sulfide minerals and the resistive silicate host rock. The main techniques used are: Seismic tomography to locate earthquakes and assist in Seismology. Reflection seismology and seismic refraction to map the surface structure of a region. Geodesy and gravity techniques, including gravity gradiometry. Magnetic techniques, including aeromagnetic surveys to map magnetic anomalies. Electrical techniques, including electrical resistivity tomography and induced polarization. Electromagnetic methods, such as magnetotellurics, ground penetrating radar, transient/time-domain electromagnetics, and SNMR. Borehole geophysics, also called well logging. Remote sensing techniques, including hyperspectral imaging. Many other techniques, or methods of integration of the above techniques, have been developed and are currently used. However these are not as common due to cost-effectiveness, wide applicability, and/or uncertainty in the results produced. Exploration geophysics is also used to map the subsurface structure of a region, to elucidate the underlying structures, to recognize spatial distribution of rock units, and to detect structures such as faults, folds and intrusive rocks.