Geophysics, the application of the science of physics to the study of the earth. Geophysicists have developed highly technical methods for investigating problems in geology, meteorology, and oceanography. Using sensitive instruments, the geophysicist measures and describes physical forces that cannot be studied with equal accuracy by direct observation.

The geophysicist is interested primarily in natural forces, such as the forces generated by earthquakes, storms, and ocean currents. The geophysicist also applies artificial forces to the earth, for test purposes. Examples are man-made explosions that send shock waves through the rocks, sounds that cause echo effects at the bottom of the sea, and radio signals that bounce off the reflecting layers high above the earth. By using these test methods, the geophysicist obtains information about the shape and composition of the earth as a whole.

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The techniques of geophysics can also be applied to localized problems. For example, the geophysicist is able to chart the rock structures that are hidden deep beneath land and water surfaces. This kind of information is helpful in locating oil and mineral deposits, underground water, and the flaws in rock formations at places where roads and dams are to be built. In addition to making observations on the ground, geophysicists make wide use of artificial satellites, which collect data by photography and through various kinds of sensing and measuring instruments.

A notable event in the history of geophysics was the International Geophysical Year (IGY) of 1957-58, a cooperative venture involving nearly 10,000 scientists from 66 countries. During the 1960's and 1970's geophysicists played a major role in the development of the theory of plate tectonics, which attempts to explain the movement of continents and the basic causes of earthquakes, volcanoes, and the formation of mountain ranges.

In the 1980's and 1990's the continued development of remote sensing instruments aided in the detection and analysis of various geophysical phenomena. These included ancient surface features buried under sediment, the deformation of the ground before an earthquake or of a volcano's surface before an eruption, and geophysical processes as compared with similar processes occurring on other bodies of the solar system.

Geophysical Instruments

One of the instruments most used by the geophysicist is the seismograph. It records the strength and speed of vibrations as they travel through the earth. The magnetometer detects the magnetic properties of rocks. The gravimeter measures the force of gravity. Geophysicists also use instruments and techniques originally developed for other purposes.

American GeophysicalUnion (AGU)

is the principal professional organization of geophysical scientists. The AGU publishes the Journal of Geophysical Research, Tectonics, and other journals. The organization was founded in 1919. Membership is abou 35,000. Headquarters are in Washington, D.C.