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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.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.The distribution of telluric current density can be used to detect variations in electrical resistivity of underground structures.Measurements of seismic waves are a source of information on the region that the waves travel through.
Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times.
In the core, they probably have little observable effect on the geomagnetic field, but slower waves such as magnetic Rossby waves may be one source of geomagnetic secular variation.
The Earth's field is roughly like a tilted dipole, but it changes over time (a phenomenon called geomagnetic secular variation).
The entire Earth can also oscillate in forms that are called normal modes or free oscillations of the Earth.
Ground motions from waves or normal modes are measured using seismographs.