Seismology (from the Greek seismos = earthquake and logos = word) is the scientific study of earthquakes and the movement of waves through the Earth. The field also includes studies of variants such as seaquakes, causes such as volcanoes and plate tectonics in general, and consequential phenomena such as tsunami.
Earthquakes (and other earth movements) produce different types of seismic waves. These waves travel through rock, and provide an effective way to "see" events and structures deep in the Earth.
One of the earliest important discoveries was that the outer core of the Earth is liquid. Pressure waves pass through the core. Transverse or shear waves that shake side-to-side require rigid material so they do not pass through the core.
The process of mapping subsurface features is a specialty called seismography . Seismic waves produced by explosions have been used to map salt domes and other oil-bearing rocks, faults (cracks in deep rock), rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.
Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, magma plumes and other large features of the inner Earth.
Seismographs also effectively discover unusual, otherwise unobserved phenomena such as large meteors striking uninhabited ocean, or underground nuclear tests. Ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been reported.
One of the first attempts at the scientific study of earthquakes occurred following the 1755 Lisbon earthquake.
- Main article: Earthquake prediction
Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and some believe that such a system would be effectively impossible. More general forecasts, however, are routinely used to establish seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time span.
Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method. Such methods have yet to be generally accepted in the seismology community.
Oldham, Richard Dixon
Sebastião de Melo, Marquis of Pombal
Richter, Charles Francis