Seismology (from the Greek seismos(σεισμός) = earthquake and λόγος,logos = knowledge ) is the scientific study of earthquakes and the propagation of elastic waves through the Earth. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer Linear elasticity is the mathematical study of how solid objects deform and become internally stressed due to prescribed loading conditions EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A tsunami ((tsuːˈnɑːmi is a series of waves created when A related field that uses geology to infer information regarding past earthquakes is paleoseismology. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Paleoseismology looks at Geologic Sediments and rocks, for signs of ancient Earthquakes It is used to supplement seismic monitoring A recording of earth motion as a function of time is called a seismogram. A seismogram is a graph output by a Seismograph. It is a record of the ground motion at a measuring station

Contents 1 Seismic Waves 2 Earthquake prediction 3 Notable seismologists 4 See also 5 References

Seismic Waves

Main article: Seismic wave

Earthquakes, and other sources, produce different types of seismic waves which travel through rock, and provide an effective way to image both sources and structures deep within the Earth. Seismic waves are Waves that travel through the Earth, most often as the result of a tectonic Earthquake, sometimes from an Explosion There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and surface waves. P-wave can also refer to a type of electronic wavefunction in atomic physics see Atomic orbital. S-wave can also refer to the lowest energy electronic wavefunction in atomic physics see Atomic orbital. The two basic kinds of surface waves (Rayleigh and Love), can be fundamentally explained in terms of interacting P- and/or S-waves. Rayleigh waves, also known as the Rayleigh-Lamb Wave or "ground roll" are a type of Surface wave. In Elastodynamics, Love waves are essentially horizontally polarized shear waves (SH waves guided by an elastic layer which is "welded" to an elastic half space on

Pressure waves (P-waves), are longitudinal waves that travel at maximum velocity within solids and are therefore the first waves to appear on a seismogram. P-wave can also refer to a type of electronic wavefunction in atomic physics see Atomic orbital. Longitudinal waves are waves that have vibrations along or parallel to their direction of travel that is waves in which the motion of the medium is in the same direction as the motion

S-waves, also called Shear waves or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. A transverse wave is a moving Wave that consists of oscillations occurring perpendicular to the direction of energy transfer Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids such as air or water.

Surface waves travel more slowly than P-waves and S-waves, but because they are guided by the surface of the Earth (and their energy is thus trapped near the Earth's surface) they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth, such as the case of a shallow earthquake.

For large enough earthquakes, one can observe the normal modes of the Earth. A normal mode of an oscillating system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency These modes are excited as discrete frequencies and can be observed for days after the generating event. The first observations were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century - the 1960 Great Chilean earthquake and the 1964 Great Alaskan earthquake. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 The twentieth century of the Common Era began on The 1960 Valdivia earthquake or Great Chilean Earthquake (Gran terremoto de Valdivia of 22 May, 1960 is the most powerful Earthquake ever Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.

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. Richard Dixon Oldham ( July 31, 1858 &ndash July 15, 1936) was an Irish geologist who in 1906 argued that the Earth Sir Harold Jeffreys ( 22 April 1891 &ndash 18 March 1989) was a mathematician statistician geophysicist and astronomer The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Pressure waves (P-waves) pass through the core. P-wave can also refer to a type of electronic wavefunction in atomic physics see Atomic orbital. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. A transverse wave is a moving Wave that consists of oscillations occurring perpendicular to the direction of energy transfer A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (seismically faster velocity) mantle.

Seismic waves produced by explosions or vibrating controlled sources are the primary method of underground exploration. An explosion is a sudden increase in Volume and release of Energy in an extreme manner usually with the generation of high Temperatures and the release Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. A salt dome is a type of structural dome formed when a thick bed of Evaporite minerals (mainly salt or Halite) found at depth intrudes vertically into Petroleum ( L petroleum, from Greek πετρέλαιον, lit In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body 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. The Chicxulub Crater (tʃikʃuˈlub is an ancient Impact crater buried underneath the Yucatán Peninsula in Mexico. Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum Geologists for Hydrocarbon deposits beneath the Earth's surface

Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. Seismic Tomography is a methodology for estimating the earth's properties This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth. A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle.

Seismographs are instruments that sense and record the motion of the Earth. Seismometers (from Greek Seism - "the shakes" - and Metro - "I measure" are instruments that measure and record motions of the ground including Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthquakes and tsunami warnings, as well as recording a variety of seismic signals arising from non-earthquake sources ranging from explosions (nuclear and chemical), to pressure variations on the ocean floor induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers. The cryosphere, derived from the Greek word kryo for " Cold " or "too cold" is the term which collectively describes the portions of Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4. 2 × 10¹³ J of effective explosive force) have been recorded by seismographs. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity A major motivation for the global instrumentation of the Earth with seismographs has been for the monitoring of nuclear testing. Nuclear weapons tests are experiments carried out to determine the effectiveness yield and explosive capability of Nuclear weapons Throughout the twentieth century most nations

One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. The 1755 Lisbon earthquake, also known as the Great Lisbon Earthquake, took place on November 1 1755 at around 940 in the morning Other especially notable earthquakes that spurred major developments in the science of seismology include the 1906 San Francisco earthquake, the 1964 Alaska earthquake and the 2004 Sumatra-Andaman earthquake. The 2004 Indian Ocean earthquake was an undersea Earthquake that occurred at 005853 UTC on December 26 2004 with an Epicentre off the west coast of An extensive list of famous earthquakes can be found on the earthquake page. An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer

Earthquake prediction

Main article: Earthquake prediction

Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events. An earthquake prediction is a Prediction that an Earthquake in a specific magnitude range will occur in a specific region and time window 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. The VAN method is an experimental method of Earthquake prediction, named after the surname initials of each of its inventors Greek Physicists Panayotis Varotsos Such methods have yet to be generally accepted in the seismology community.

Notable seismologists

See also

References

Keiiti Aki ( March 3 1930 - May 17 2005) was a Professor, Seismologist, Author and Mentor. Bruce Bolt ( February 15, 1930 – July 21, 2005) was a Professor of Earth and Planetary Science at the University of California Berkeley Adam Dziewoński (b 1936 in Lwów, then a part of Poland, currently a part of Ukraine) is a Polish-American Geophysicist who has made seminal Prince Boris Borisovich Galitzine (b St Petersburg, February 18 ( O Grigoriy Aleksandrovich Gamburtsev (Григорий Александрович Гамбурцев ( &ndash June 28, 1955) was a Soviet seismologist Beno Gutenberg ( June 4, 1889 &ndash January 25, 1960) was a German-born Seismologist who made several important contributions to Kate Hutton, nicknamed the Earthquake Lady or Dr Kate, is staff seismologist at the California Institute of Technology in Pasadena Sir Harold Jeffreys ( 22 April 1891 &ndash 18 March 1989) was a mathematician statistician geophysicist and astronomer Hiroo Kanamori (金森 博雄 Kanamori Hiroo; October 17, 1936 — is a Japanese Seismologist who has made fundamental contributions Vladimir Keilis-Borok was born in Moscow, Russia on July 31, 1921. Leon Knopoff (born 1925 is a Geophysicist and Musicologist. He received his education at Caltech, graduating in 1949 with a PhD in physics and after holding Inge Lehmann ( May 13, 1888 &ndash February 21, 1993) Fellow of the Royal Society of London, was a Danish Giuseppe Mercalli ( May 21, 1850 - March 19, 1914) was an Italian Volcanologist. John Milne (1850 &ndash 31 July 1913) was the British Geologist and mining Engineer who invented the Seismograph. Andrija Mohorovičić (ˈandrija mɔhɔːrɔvitʃiʨ ( January 23 1857 &ndash December 18, 1936) was a notable Croatian Meteorologist Richard Dixon Oldham ( July 31, 1858 &ndash July 15, 1936) was an Irish geologist who in 1906 argued that the Earth Vassilis Papazachos (Βασίλης Παπαζάχος is a Greek seismologist. Sebastião José de Carvalho e Melo 1st Count of Oeiras 1st Marquis of Pombal (in Portuguese, Marquês de Pombal, pron Frank Press (born December 4, 1924) is an American geophysicist. Charles Francis Richter ( April 26, 1900 &ndash September 30, 1985) was an American seismologist and physicist Panayiotis Varotsos (Παναγιώτης Βαρώτσος is a Greek physicist (b Zhang Heng ( (CE 78–139 was an astronomer, mathematician, inventor, geographer, cartographer, artist, poet This article refers to the use of computers to estimate losses caused by disasters A cryoseism known as a frost quake may be caused by a sudden Cracking action in frozen soil or rock saturated with Water or Ice. Engineering Geology is the application of the geologic sciences to engineering practice for the purpose of assuring that the geologic factors affecting the location design construction Geophysics, a major discipline of Earth sciences, is the study of the Earth by quantitative physical methods especially by seismic, electromagnetic Helioseismology is the study of the propagation of Pressure waves in the Sun. IRIS ( I ncorporated R esearch I nstitutions for S eismology is a university research consortium dedicated to exploring the Earth's interior through Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Reflection seismology (or seismic reflection) is a method of Exploration geophysics that uses the principles of Seismology to estimate the properties of Seismometers (from Greek Seism - "the shakes" - and Metro - "I measure" are instruments that measure and record motions of the ground including This article is about artificial seismic sources For natural seismic sources see Earthquake, Volcano, and related articles Volcanology (also spelled vulcanology) is the study of Volcanoes, Lava, Magma, and related geological and Geophysical phenomena

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