Geophysicists study the physical structure and behaviour of the earth. They study rocks, oceans, gravity, and magnetic and electrical fields, in an effort to understand the earth's origins and better understand its behaviour. The data that geophysicists collect and interpret can be used to locate underground water sources, geological faults and oil, gas and mineral deposits. This information can be used to determine any extra precautions necessary to ensure the safety and stability of buildings, as well as locating economically viable mine sites. Geophysicists may also perform laboratory and field studies, ground and drill hole surveys.