Seismology
It also includes studies of the environmental effects of earthquakes such as tsunamis; other seismic sources such as volcanoes, plate tectonics, glaciers, rivers, oceanic microseisms, and the atmosphere; and artificial processes such as explosions.
[1][2][3] In the 17th century, Athanasius Kircher argued that earthquakes were caused by the movement of fire within a system of channels inside the Earth.
Martin Lister (1638–1712) and Nicolas Lemery (1645–1715) proposed that earthquakes were caused by chemical explosions within the Earth.
Michell determined that earthquakes originate within the Earth and were waves of movement caused by "shifting masses of rock miles below the surface".
[8] In 1897, Emil Wiechert's theoretical calculations led him to conclude that the Earth's interior consists of a mantle of silicates, surrounding a core of iron.
The development of this theory depended on the considerable progress of earlier independent streams of work on the behavior of elastic materials and in mathematics.
An 80 kg (180 lb) Wiechert seismograph was brought to the Mexican city of Xalapa by rail after the earthquake.
[17] In 1926, Harold Jeffreys was the first to claim, based on his study of earthquake waves, that below the mantle, the core of the Earth is liquid.
For example, the Chicxulub Crater, which was caused by an impact that has been implicated in the extinction of the dinosaurs, was localized to Central America by analyzing ejecta in the Cretaceous–Paleogene boundary, and then physically proven to exist using seismic maps from oil exploration.
Networks of seismographs continuously record ground motions around the world to facilitate the monitoring and analysis of global earthquakes and other sources of seismic activity.
Seismometers also record signals from non-earthquake sources ranging from explosions (nuclear and chemical), to local noise from wind[24] or anthropogenic activities, to incessant signals generated at the ocean floor and coasts induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers.
Above-ocean meteor strikes with energies as high as 4.2 × 1013 J (equivalent to that released by an explosion of ten kilotons of TNT) have been recorded by seismographs, as have a number of industrial accidents and terrorist bombs and events (a field of study referred to as forensic seismology).
Because seismic waves commonly propagate efficiently as they interact with the internal structure of the Earth, they provide high-resolution noninvasive methods for studying the planet's interior.
One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the earth is liquid.
Processing readings from many seismometers using seismic tomography, seismologists have mapped the mantle of the earth to a resolution of several hundred kilometers.
This has enabled scientists to identify convection cells and other large-scale features such as the large low-shear-velocity provinces near the core–mantle boundary.
[25] Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction.
Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method.
[29] It generally applied to the branch of seismology that deals with the assessment of the seismic hazard of a site or region for the purposes of earthquake engineering.
