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Encyclopedia > Seismology

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. 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 related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram. Image File history File links Question_book-3. ... Image File history File links Broom_icon. ... This article is about the natural seismic phenomenon. ... // Linear elasticity The linear theory of elasticity models the macroscopic mechanical properties of solids assuming small deformations. ... This article is about Earth as a planet. ... The tsunami that struck Malé in the Maldives on December 26, 2004. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Paleoseismology is the study of ancient earthquakes as shown by the deformation of rocks. ... A seismogram is a graph output by a seismograph. ...

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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. There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and surface waves. The two basic kinds of surface waves (Rayleigh and Love), can be fundamentally explained in terms of interacting P- and/or S-waves. Body waves and surface waves Earthquake wave paths p-wave and s-wave from seismograph A seismic wave is a wave that travels through the Earth, most often as the result of a tectonic earthquake, sometimes from an explosion. ... Plane P-wave Representation of the propagation of a P-wave on a 2d grid (empirical shape) Of the two types of elastic body waves (named because they travel through the body of the Earth) that are produced by earthquakes and recorded by seismometers. ... A type of seismic wave, the S-wave, sometimes called an elastic S-wave, moves in a shear or transverse wave, so motion is perpendicular to the direction of wave propagation. ... Rayleigh waves, also known as the Rayleigh-Lamb Wave or ground roll, are a type of surface wave. ... In seismology, Love waves (also named Q waves) are surface seismic waves that cause horizontal shifting of the earth during an earthquake. ...


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. A pressure wave in a fluid is a travelling disturbance consisting in a local change of pressure (hence the name). ... Longitudinal waves are waves that have vibrations along or parallel to their direction of travel. ...


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. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids such as air or water. In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ... Surface waves in water This article is about waves in the most general scientific sense. ... A light wave is an example of a transverse wave. ...


Surface waves travel more slowly than P-waves and S-waves, however, because they are guided by the surface of the Earth, and their energy is 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.


For large enough earthquakes, one can observe the normal modes of the Earth. 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. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth. Normal modes in an oscillating system are special solutions where all the parts of the system are oscillating with the same frequency (called normal frequencies or allowed frequencies). ... The 1960s decade refers to the years from the beginning of 1960 to the end of 1969. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... Map showing the areas affected by the tsunami The Great Chilean Earthquake or Valdivian Earthquake (Terremoto de Valdivia in Spanish) of 22 May 1960 is the most intense earthquake ever recorded, rating a 9. ... Earthquake Damage, Anchorage The Good Friday Earthquake (also called the Great Alaska Earthquake) of Friday, March 27, 1964 (Good Friday, a Christian holy day associated with a historical earthquake[1]), 5:36 P.M. AST (03:36 3/27 UTC) had a magnitude of 9. ...


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. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. 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 (sesimically faster velocity) mantle. Richard Dixon Oldham (July 31, 1858 – July 15, 1936) was a British geologist who, in 1906, argued that the Earth must have a molten interior as S waves were not able to travel through liquids nor through the Earths interior. ... Sir Harold Jeffreys (22 April 1891 – 18 March 1989) was a mathematician, statistician, geophysicist, and astronomer. ... For other uses, see Liquid (disambiguation). ... A pressure wave in a fluid is a travelling disturbance consisting in a local change of pressure (hence the name). ... A light wave is an example of a transverse wave. ... In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ... Surface waves in water This article is about waves in the most general scientific sense. ...


Seismic waves produced by explosions or vibrating controlled sources are the primary method of underground exploration. 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. 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. A salt dome is formed when a thick bed of evaporite minerals (mainly salt, or halite) found at depth intrudes vertically into surrounding rock strata, forming a diapir. ... Petro redirects here. ... This article is about the geological substance. ... Old fault exposed by roadcut near Harrisburg, Pennsylvania. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Tycho crater on Earths moon. ... Radar topography reveals the 180 kilometer (112 mile) wide ring of the crater (image courtesy NASA/JPL-Caltech) Chicxulub Crater (IPA: ) (cheek-shoo-LOOB) is an ancient impact crater buried underneath the Yucatán Peninsula, with its center located approximately underneath the town of Chicxulub, Yucatán, Mexico. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Oil exploration is the search by petroleum geologists for hydrocarbon deposits beneath the Earths surface. ...


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, mantle plumes and other large-scale features of the inner Earth. Seismic tomography uses digital seismographic records to image the interior of the Earth. ... A lava lamp illustrates the basic concept of a mantle plume. ...


Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthqaukes and tsunami warnings, as well as recording a variety of seismic signals arising from nonearthquake phenomena such as large meteors entering the atmosphere, pressure variations on the ocean floor induced by ocean waves (the global microseism), cryospheric events associated with large icebergs and glaciers, or underground nuclear tests. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been reported. Seismographs (in Greek seismos = earthquake and graphein = write) are used by seismologists to record seismic waves. ... The cryosphere, derived from the Greek word kryos for frost or icy cold, is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground... The joule (IPA: or ) (symbol: J) is the SI unit of energy. ...


One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. 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. An extensive list of famous earthquakes can be found on the earthquake page. This 1755 copper engraving shows the ruins of Lisbon in flames and a tsunami overwhelming the ships in the harbor. ... San Francisco Earthquake redirects here. ... Earthquake Damage, Anchorage The Good Friday Earthquake (also called the Great Alaska Earthquake) of Friday, March 27, 1964 (Good Friday, a Christian holy day), 5:36 P.M. AST (03:36 3/28 UTC) was the most powerful earthquake in U.S. and North American history, and the third most... Tsunami strikes Ao Nang, Thailand. ... This article is about the natural seismic phenomenon. ...


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. 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. Seismic hazard map of the San Francisco Bay Area, showing the probability of a major earthquake occurring by 2032 An earthquake prediction is a prediction that an earthquake in a specific magnitude range will occur in a specific region and time window. ...


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. The VAN method is an experimental earthquake prediction method. ...


Notable seismologists

Keiiti Aki (March 3, 1930 - May 17, 2005) was a professor, seismologist, author and mentor. ... Bruce Bolt (born February 15, 1930 - died July 21, 2005) was a Professor of Earth and Planetary Science at the University of California, Berkeley. ... Adam Dziewonski (* 1936, in Ukraine, formerly Poland) is a US geophysicist who has made seminal contributions to the determination of the large-scale structure of the Earths interior and the nature of earthquakes using seismological methods. ... Prince Boris Borisovich Galitzine (b. ... Beno Gutenberg (June 4, 1889 – January 25, 1960) was a German-born seismologist who made several important contributions to the science. ... Kate Hutton, nicknamed the Earthquake Lady or Dr. Kate, is staff seismologist at the California Institute of Technology in Pasadena, California. ... Sir Harold Jeffreys (22 April 1891 – 18 March 1989) was a mathematician, statistician, geophysicist, and astronomer. ... Hiroo Kanamori (金森 博雄 Kanamori Hiroo; October 17, 1936—) is a seismologist who has made fundamental contributions to understanding the physics of earthquakes and the tectonic processes that cause them. ... Vladimir Keilis-Borok was born in Moscow, Russia on July 31, 1921. ... Inge Lehmann (May 13, 1888 - February 21, 1993), Fellow of the Royal Society (London) 1969, was a Danish seismologist who, in 1936, argued that the Earth must not only have a molten interior, but a solid core at the center, which deflects P waves. ... Giuseppe Mercalli (born May 21, 1850) was an Italian volcanologist. ... John Milne (1850 – 1913) was the English geologist and mining engineer who invented the seismograph. ... Andrija Mohorovičić (c. ... Richard Dixon Oldham (July 31, 1858 – July 15, 1936) was a British geologist who, in 1906, argued that the Earth must have a molten interior as S waves were not able to travel through liquids nor through the Earths interior. ... Vassilis Papazachos (Greek: Βασίλης Παπαζάχος) is a Greek seismologist. ... The Marquis of Pombal, or Marquês de Pombal, (13 May 1699 - 15 May 1782) was a Portuguese politician and statesman, prime minister of king Joseph I of Portugal throughout his reign. ... Dr. Frank Press (born December 4, 1924) is an American geophysicist. ... Charles Francis Richter (April 26, 1900 – September 30, 1985), was an American seismologist, born outside of Hamilton, Ohio. ... Panayotis Varotsos (Greek: Παναγιώτης Βαρώτσος) is a Greek physicist (b. ... For other uses, see Zhang Heng (disambiguation). ...

See also

Catastrophe modeling (also known as cat modeling) is the process of using computer-assisted calculations to estimate the losses that could be sustained by a portfolio of properties due to a catastrophic event such as a hurricane or earthquake. ... A cryoseism, also known as a frost quake[1][2] or ice quake, is a non-tectonic seismic event caused by a sudden freezing action in soil or rock materials saturated with water or ice. ... Engineering Geology is the application of the science of geology to the understanding of geologic phenomena and the engineering solution of geologic hazards and other geologic problems for society. ... ‹ The template below has been proposed for deletion. ... A computer generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. ... The IRIS Consortium is a trans-University research project standing for Incorporated Research Institutions for Seismology. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Seismic reflection data Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earths subsurface from reflected seismic waves. ... Seismometers is of Greek origin and comes from Seism - the shakes and Meteo - I measure are instruments that measure and record motions of the ground, including those of seismic waves generated by earthquakes, nuclear explosions, and other seismic sources. ... A seismic source generates controlled seismic energy that is used in both reflection and refraction seismic surveys. ... Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma, and related geological phenomena. ...

References


  Results from FactBites:
 
AGU: Seismology Section Home page (210 words)
The Seismology Section is concerned with the study of the Earth's internal structure, its deep interior and dynamics, how the Earth was formed, and the physical phenomena that cause earthquakes.
Seismology attracts considerable public interest and support because of its contributions to society in mitigating earthquake hazards, monitoring nuclear explosions both for military intelligence and arms control, and finding oil.
Now that seismology is a data-based science, modern seismology has many opportunities for people who take an analytical approach to the geophysical sciences, such as those skilled in classical physics, applied mathematics, time series analysis, and computer sciences.
  More results at FactBites »

 
 

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