Measurements of seismic waves are a source of information on the region that the waves travel through.
If the density or composition of the rock changes suddenly, some waves are reflected.
If the waves come from a localized source such as an earthquake or explosion, measurements at more than one location can be used to locate the source.
The locations of earthquakes provide information on plate tectonics and mantle convection.
Geophysics is applied to societal needs, such as mineral resources, mitigation of natural hazards and environmental protection.
In Exploration Geophysics, Geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, locate groundwater, find archaeological relics, determine the thickness of glaciers and soils, and assess sites for environmental remediation.
However, modern geophysics organizations use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial relations; and analogous problems associated with the Moon and other planets.
Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times.
Geophysicists can also provide the electric current themselves (see induced polarization and electrical resistivity tomography).
Electromagnetic waves occur in the ionosphere and magnetosphere as well as the Earth's outer core. Electromagnetic waves may also be generated by earthquakes (see seismo-electromagnetics).
Dawn chorus is believed to be caused by high-energy electrons that get caught in the Van Allen radiation belt. In the Earth's outer core, electric currents in the highly conductive liquid iron create magnetic fields by electromagnetic induction (see geodynamo).
Alfvén waves are magnetohydrodynamic waves in the magnetosphere or the Earth's core.
Some measure spontaneous potential, a potential that arises in the ground because of man-made or natural disturbances. They have two causes: electromagnetic induction by the time-varying, external-origin geomagnetic field and motion of conducting bodies (such as seawater) across the Earth's permanent magnetic field.