geophysics

Geophysics is the science that uses physical principles to study the Earth's interior, structure, composition, and processes. It applies physics to natural phenomena such as gravity, magnetism, heat flow, and seismic waves to infer properties of rocks and fluids beneath the surface. Geophysics overlaps with geology and engineering and underpins many practical activities, from resource exploration to environmental monitoring.

Major subfields include seismology, which studies elastic waves to probe Earth's interior and monitor earthquakes; geomagnetism and paleomagnetism; gravity and geodesy; and geoelectrical methods that use electrical conductivity to probe subsurface materials. Electromagnetic techniques such as magnetotellurics and ground-penetrating radar are common, and imaging methods include seismic reflection and refraction, tomography, electrical-resistivity, gravity surveying, and borehole logging. Data are interpreted with forward modeling and inverse methods to estimate properties such as density, velocity, porosity, and fluid content.

Applications include resource exploration (oil, gas, and minerals), groundwater and contaminant mapping, geotechnical site characterization, civil engineering projects such as foundations, tunnels, and dams, seismic hazard assessment, and volcanic and geothermal monitoring.

History: The field emerged in the 19th and early 20th centuries with advances in gravity measuring, seismology, and subsurface sounding; it has since become essential to Earth science and engineering.