What is Geophysics?

Geophysics is a branch of earth sciences investigating the physical processes and phenomena occurring in the earth by combining physics, mathematics and geology. 
Geophysics is the subsurface site characterization of the geology, geological structure, groundwater, contamination, and human artifacts beneath the Earth's surface, based on the lateral and vertical mapping of physical property variations that are remotely sensed using non-invasive technologies. Many of these technologies are traditionally used for exploration of economic materials such as groundwater, metals, and hydrocarbons.
Geophysics is the non-invasive investigation of subsurface conditions in the Earth through measuring, analyzing and interpreting physical fields at the surface. Some studies are used to determine what is directly below the surface (the upper meters or so); other investigations extend to depths of 100's of meters or more.
Geophysical methods are used to study large scale Earth Structure, to measure the exact shape and size of the planet (Geodesy), to study the dynamics of the Earth’s interior and tectonic plates (Geodynamics), to study the history of Earth’s magnetic field and its present state (Geomagnetism), to study the physical properties of rocks and minerals at or near the surface, as well as those in the core (Mineral Physics)  and finally, to study the physical causes and effects of earthquakes (Seismology)