Seismology

Seismology (/saɪzˈmɒlədʒi, saɪs-/; from Ancient Greek σεισμός (seismós) meaning "earthquake" and -λογία (-logía) meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic waves through the Earth or other planetary bodies. It also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, glacial, fluvial, oceanic microseism, atmospheric, and artificial processes such as explosions and human activities. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of Earth motion as a function of time, created by a seismograph is called a seismogram. A seismologist is a scientist works in basic or applied seismology.

Animation of tsunami triggered by the 2004 Indian Ocean earthquake

History

Scholarly interest in earthquakes can be traced back to antiquity. Early speculations on the natural causes of earthquakes were included in the writings of Thales of Miletus (c. 585 BCE), Anaximenes of Miletus (c. 550 BCE), Aristotle (c. 340 BCE), and Zhang Heng (132 CE).

In 132 CE, Zhang Heng of China's Han dynasty designed the first known seismoscope.^[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.^[4]

The Lisbon earthquake of 1755, coinciding with the general flowering of science in Europe, set in motion intensified scientific attempts to understand the behaviour and causation of earthquakes. The earliest responses include work by John Bevis (1757) and John Michell (1761). Michell determined that earthquakes originate within the Earth and were waves of movement caused by "shifting masses of rock miles below the surface".^[5]

In response to a series of earthquakes near Comrie in Scotland in 1839, a committee was formed in the United Kingdom in order to produce better detection methods for earthquakes. The outcome of this was the production of one of the first modern seismometers by James David Forbes, first presented in a report by David Milne-Home in 1842.^[6] This seismometer was an inverted pendulum, which recorded the measurements of seismic activity through the use of a pencil placed on paper above the pendulum. The designs provided did not prove effective, according to Milne's reports.^[6]

From 1857, Robert Mallet laid the foundation of modern instrumental seismology and carried out seismological experiments using explosives. He is also responsible for coining the word "seismology."^[7]

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.^[8]

In 1906 Richard Dixon Oldham identified the separate arrival of P-waves, S-waves and surface waves on seismograms and found the first clear evidence that the Earth has a central core.^[9]

In 1909, Andrija Mohorovičić, one of the founders of modern seismology,^[10][11][12] discovered and defined the Mohorovičić discontinuity.^[13] Usually referred to as the "Moho discontinuity" or the "Moho," it is the boundary between the Earth's crust and the mantle. It is defined by the distinct change in velocity of seismological waves as they pass through changing densities of rock.^[14]

In 1910, after studying the April 1906 San Francisco earthquake, Harry Fielding Reid put forward the "elastic rebound theory" which remains the foundation for modern tectonic studies. 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.^[15]

An early scientific study of aftershocks from a destructive earthquake came after the January 1920 Xalapa earthquake. An 80 kg (180 lb) Wiechert seismograph was brought to the Mexican city of Xalapa by rail after the earthquake. The instrument was deployed to record its aftershocks. Data from the seismograph would eventually determine that the mainshock was produced along a shallow crustal fault.^[16]

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.^[17]

In 1937, Inge Lehmann determined that within Earth's liquid outer core there is a solid inner core.^[18]

By the 1960s, Earth science had developed to the point where a comprehensive theory of the causation of seismic events and geodetic motions had come together in the now well-established theory of plate tectonics.^{[citation needed]}

Types of seismic wave

Main article: Seismic wave

 

Seismogram records showing the three components of ground motion. The red line marks the first arrival of P-waves; the green line, the later arrival of S-waves.

Seismic waves are elastic waves that propagate in solid or fluid materials. They can be divided into body waves that travel through the interior of the materials; surface waves that travel along surfaces or interfaces between materials; and normal modes, a form of standing wave.

Body waves

There are two types of body waves, pressure waves or primary waves (P-waves) and shear or secondary waves (S-waves). P-waves are longitudinal waves that involve compression and expansion in the direction that the wave is moving and are always the first waves to appear on a seismogram as they are the fastest moving waves through solids. S-waves are transverse waves that move perpendicular to the direction of propagation. S-waves are slower than P-waves. Therefore, they appear later than P-waves on a seismogram. Fluids cannot support transverse elastic waves because of their low shear strength, so S-waves only travel in solids.^[19]

Surface waves

Surface waves are the result of P- and S-waves interacting with the surface of the Earth. These waves are dispersive, meaning that different frequencies have different velocities. The two main surface wave types are Rayleigh waves, which have both compressional and shear motions, and Love waves, which are purely shear. Rayleigh waves result from the interaction of P-waves and vertically polarized S-waves with the surface and can exist in any solid medium. Love waves are formed by horizontally polarized S-waves interacting with the surface, and can only exist if there is a change in the elastic properties with depth in a solid medium, which is always the case in seismological applications. Surface waves travel more slowly than P-waves and S-waves because they are the result of these waves traveling along indirect paths to interact with Earth's surface. Because they travel along the surface of the Earth, their energy decays less rapidly than body waves (1/distance² vs. 1/distance³), and thus the shaking caused by surface waves is generally stronger than that of body waves, and the primary surface waves are often thus the largest signals on earthquake seismograms. Surface waves are strongly excited when their source is close to the surface, as in a shallow earthquake or a near-surface explosion, and are much weaker for deep earthquake sources.^[19]

Normal modes

See also: Free oscillations of the Earth

Both body and surface waves are traveling waves; however, large earthquakes can also make the entire Earth "ring" like a resonant bell. This ringing is a mixture of normal modes with discrete frequencies and periods of approximately an hour or shorter. Normal mode motion caused by a very large earthquake can be observed for up to a month after the event.^[19] The first observations of normal modes 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 Valdivia earthquake and the 1964 Alaska earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.

Earthquakes

Main articles: Earthquake and Lists of earthquakes

One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other notable earthquakes that spurred major advancements in the science of seismology include the 1857 Basilicata earthquake, the 1906 San Francisco earthquake, the 1964 Alaska earthquake, the 2004 Sumatra-Andaman earthquake, and the 2011 Great East Japan earthquake.

Controlled seismic sources

See also: Reflection seismology

Seismic waves produced by explosions or vibrating controlled sources are one of the primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics). Controlled-source seismology has been used to map salt domes, anticlines and other geologic traps in petroleum-bearing rocks, faults, rock types, and long-buried giant meteor craters. 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.^[20]

Detection of seismic waves

 

Installation for a temporary seismic station, north Iceland highland.

Seismometers are sensors that detect and record the motion of the Earth arising from elastic waves. Seismometers may be deployed at the Earth's surface, in shallow vaults, in boreholes, or underwater. A complete instrument package that records seismic signals is called a seismograph. 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. Rapid location of earthquakes makes tsunami warnings possible because seismic waves travel considerably faster than tsunami waves. Seismometers also record signals from non-earthquake sources ranging from explosions (nuclear and chemical), to local noise from wind^[21] 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). A major long-term motivation for the global seismographic monitoring has been for the detection and study of nuclear testing.

Mapping Earth's interior

Main article: Earth's interior

 

Seismic velocities and boundaries in the interior of the Earth sampled by seismic waves

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. Since S-waves do not pass through liquids, the liquid core causes a "shadow" on the side of the planet opposite the earthquake where no direct S-waves are observed. In addition, P-waves travel much slower through the outer core than the mantle.

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.^[22]

Seismology and society

Earthquake prediction

Main article: Earthquake prediction

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. 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 useful warning of impending seismic events. However, more general forecasts routinely predict seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time-span, and they are routinely used in earthquake engineering.

Public controversy over earthquake prediction erupted after Italian authorities indicted six seismologists and one government official for manslaughter in connection with a magnitude 6.3 earthquake in L'Aquila, Italy on April 5, 2009. The indictment has been widely perceived^{[by whom?]} as an indictment for failing to predict the earthquake and has drawn condemnation from the American Association for the Advancement of Science and the American Geophysical Union. The indictment claims that, at a special meeting in L'Aquila the week before the earthquake occurred, scientists and officials were more interested in pacifying the population than providing adequate information about earthquake risk and preparedness.^[23]

Engineering seismology

Engineering seismology is the study and application of seismology for engineering purposes.^[24] 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. It is, therefore, a link between earth science and civil engineering.^[25] There are two principal components of engineering seismology. Firstly, studying earthquake history (e.g. historical^[25] and instrumental catalogs^[26] of seismicity) and tectonics^[27] to assess the earthquakes that could occur in a region and their characteristics and frequency of occurrence. Secondly, studying strong ground motions generated by earthquakes to assess the expected shaking from future earthquakes with similar characteristics. These strong ground motions could either be observations from accelerometers or seismometers or those simulated by computers using various techniques,^[28] which are then often used to develop ground motion prediction equations^[29] (or ground-motion models)[1].

Tools

Seismological instruments can generate large amounts of data. Systems for processing such data include:

• CUSP (Caltech-USGS Seismic Processing)^[30]
• RadExPro seismic software
• SeisComP3^[31]

Notable seismologists

See also: Category:Seismologists

• Aki, Keiiti
• Ambraseys, Nicholas
• Anderson, Don L.
• Bolt, Bruce
• Claerbout, Jon
• Dziewonski, Adam Marian
• Ewing, Maurice
• Galitzine, Boris Borisovich
• Gamburtsev, Grigory A.
• Gutenberg, Beno
• Hough, Susan
• Jeffreys, Harold
• Jones, Lucy
• Kanamori, Hiroo
• Keilis-Borok, Vladimir
• Knopoff, Leon
• Lehmann, Inge
• Macelwane, James
• Mallet, Robert
• Mercalli, Giuseppe
• Milne, John
• Mohorovičić, Andrija
• Oldham, Richard Dixon
• Omori, Fusakichi
• Sebastião de Melo, Marquis of Pombal
• Press, Frank
• Richards, Paul G.
• Richter, Charles Francis
• Sekiya, Seikei
• Sieh, Kerry
• Paul G. Silver
• Stein, Ross
• Tucker, Brian
• Vidale, John
• Wen, Lianxing
• Winthrop, John
• Zhang Heng

See also

•  Geophysics portal
•  Physics portal

• Asteroseismology – Study of oscillations in stars (starquakes)
• Cryoseism – Non-tectonic seismic event
• Earthquake swarm – Series of localized seismic events within a short time period
• Engineering geology – Application of geology to engineering practice
• Epicentral distance
• Harmonic tremor – Sustained ground vibration associated with underground movement of magma or volcanic gas
• Helioseismology – SunquakePages displaying short descriptions with no spaces
• IRIS Consortium – university research consortium dedicated to exploring the Earth's interior through the collection and distribution of seismographic dataPages displaying wikidata descriptions as a fallback
• Isoseismal map – Type of map used in seismology
• Linear seismic inversion – Interpretation of seismic data using linear model
• Lunar seismology – Study of ground motions of the Moon
• Marsquake – Seismic event occurring on Mars
• Quake (natural phenomenon) – Surface shaking on interstellar bodies in general
• Seismic interferometry
• Seismic loading – basic concept in earthquake engineeringPages displaying wikidata descriptions as a fallback
• Seismic migration – Measurement process
• Seismic noise – generic name for a relatively persistent vibration of the groundPages displaying wikidata descriptions as a fallback
• Seismic performance analysis – Study of the response of buildings and structures to earthquakesPages displaying short descriptions of redirect targets
• Seismic velocity structure – Seismic wave velocity variation
• Seismite – Sediment/structure shaken seismically
• Seismo-electromagnetics – Electro-magnetic phenomena
• Seismotectonics – study of how tectonic faults influence earthquakesPages displaying wikidata descriptions as a fallback
• Stabilized inverse Q filtering

Notes

1. Needham, Joseph (1959). Science and Civilization in China, Volume 3: Mathematics and the Sciences of the Heavens and the Earth. Cambridge: Cambridge University Press. pp. 626–635. Bibcode:1959scc3.book.....N.
2. Dewey, James; Byerly, Perry (February 1969). "The early history of seismometry (to 1900)". Bulletin of the Seismological Society of America. 59 (1): 183–227.
3. Agnew, Duncan Carr (2002). "History of seismology". International Handbook of Earthquake and Engineering Seismology. International Geophysics. 81A: 3–11. doi:10.1016/S0074-6142(02)80203-0. ISBN 9780124406520.
4. Udías, Agustín; Arroyo, Alfonso López (2008). "The Lisbon earthquake of 1755 in Spanish contemporary authors". In Mendes-Victor, Luiz A.; Oliveira, Carlos Sousa; Azevedo, João; Ribeiro, Antonio (eds.). The 1755 Lisbon earthquake: revisited. Springer. p. 14. ISBN 9781402086090.
5. Member of the Royal Academy of Berlin (2012). The History and Philosophy of Earthquakes Accompanied by John Michell's 'conjectures Concerning the Cause, and Observations upon the Ph'nomena of Earthquakes'. Cambridge Univ Pr. ISBN 9781108059909.
6. Oldroyd, David (2007). "The Study of Earthquakes in the Hundred Years Following Lisbon Earthquake of 1755". Researchgate. Earth sciences history: journal of the History of the Earth Sciences Society. Retrieved 4 October 2022.
7. Society, The Royal (2005-01-22). "Robert Mallet and the 'Great Neapolitan earthquake' of 1857". Notes and Records. 59 (1): 45–64. doi:10.1098/rsnr.2004.0076. ISSN 0035-9149. S2CID 71003016.
8. Barckhausen, Udo; Rudloff, Alexander (14 February 2012). "Earthquake on a stamp: Emil Wiechert honored". Eos, Transactions American Geophysical Union. 93 (7): 67. Bibcode:2012EOSTr..93...67B. doi:10.1029/2012eo070002.
9. "Oldham, Richard Dixon". Complete Dictionary of Scientific Biography. Vol. 10. Charles Scribner's Sons. 2008. p. 203.
10. "Andrya (Andrija) Mohorovicic". Penn State. Archived from the original on 26 June 2013. Retrieved 30 January 2021.
11. "Mohorovičić, Andrija". Encyclopedia.com. Archived from the original on 1 February 2021. Retrieved 30 January 2021.
12. "Andrija Mohorovičić (1857–1936)—On the occasion of the 150th anniversary of his birth". seismosoc.org. Archived from the original on 1 February 2021. Retrieved 30 January 2021.
13. Andrew McLeish (1992). Geological science (2nd ed.). Thomas Nelson & Sons. p. 122. ISBN 978-0-17-448221-5.
14. Rudnick, R. L.; Gao, S. (2003-01-01), Holland, Heinrich D.; Turekian, Karl K. (eds.), "3.01 – Composition of the Continental Crust", Treatise on Geochemistry, Pergamon, 3: 659, Bibcode:2003TrGeo...3....1R, doi:10.1016/b0-08-043751-6/03016-4, ISBN 978-0-08-043751-4, retrieved 2019-11-21
15. "Reid's Elastic Rebound Theory". 1906 Earthquake. United States Geological Survey. Retrieved 6 April 2018.
16. Suárez, G.; Novelo‐Casanova, D. A. (2018). "A Pioneering Aftershock Study of the Destructive 4 January 1920 Jalapa, Mexico, Earthquake". Seismological Research Letters. 89 (5): 1894–1899. doi:10.1785/0220180150. S2CID 134449441.
17. Jeffreys, Harold (1926-06-01). "On the Amplitudes of Bodily Seismic Waues". Geophysical Journal International. 1: 334–348. Bibcode:1926GeoJ....1..334J. doi:10.1111/j.1365-246X.1926.tb05381.x. ISSN 1365-246X.
18. Hjortenberg, Eric (December 2009). "Inge Lehmann's work materials and seismological epistolary archive". Annals of Geophysics. 52 (6). doi:10.4401/ag-4625.
19. Gubbins 1990
20. Schulte et al. 2010
21. Naderyan, Vahid; Hickey, Craig J.; Raspet, Richard (2016). "Wind-induced ground motion". Journal of Geophysical Research: Solid Earth. 121 (2): 917–930. Bibcode:2016JGRB..121..917N. doi:10.1002/2015JB012478.
22. Wen & Helmberger 1998
23. Hall 2011
24. Plimer, Richard C. SelleyL. Robin M. CocksIan R., ed. (2005-01-01). "Editors". Encyclopaedia of Geology. Oxford: Elsevier. pp. 499–515. doi:10.1016/b0-12-369396-9/90020-0. ISBN 978-0-12-369396-9.
25. Ambraseys, N. N. (1988-12-01). "Engineering seismology: Part I". Earthquake Engineering & Structural Dynamics. 17 (1): 1–50. doi:10.1002/eqe.4290170101. ISSN 1096-9845.
26. Wiemer, Stefan (2001-05-01). "A Software Package to Analyze Seismicity: ZMAP". Seismological Research Letters. 72 (3): 373–382. doi:10.1785/gssrl.72.3.373. ISSN 0895-0695.
27. Bird, Peter; Liu, Zhen (2007-01-01). "Seismic Hazard Inferred from Tectonics: California". Seismological Research Letters. 78 (1): 37–48. doi:10.1785/gssrl.78.1.37. ISSN 0895-0695.
28. Douglas, John; Aochi, Hideo (2008-10-10). "A Survey of Techniques for Predicting Earthquake Ground Motions for Engineering Purposes" (PDF). Surveys in Geophysics. 29 (3): 187–220. Bibcode:2008SGeo...29..187D. doi:10.1007/s10712-008-9046-y. ISSN 0169-3298. S2CID 53066367.
29. Douglas, John; Edwards, Benjamin (2016-09-01). "Recent and future developments in earthquake ground motion estimation" (PDF). Earth-Science Reviews. 160: 203–219. Bibcode:2016ESRv..160..203D. doi:10.1016/j.earscirev.2016.07.005.
30. Lee, W. H. K.; S. W. Stewart (1989). "Large-Scale Processing and Analysis of Digital Waveform Data from the USGS Central California Microearthquake Network". Observatory seismology: an anniversary symposium on the occasion of the centennial of the University of California at Berkeley seismographic stations. University of California Press. p. 86. ISBN 9780520065826. Retrieved 2011-10-12. The CUSP (Caltech-USGS Seismic Processing) System consists of on-line real-time earthquake waveform data acquisition routines, coupled with an off-line set of data reduction, timing, and archiving processes. It is a complete system for processing local earthquake data ...
31. Akkar, Sinan; Polat, Gülkan; van Eck, Torild, eds. (2010). Earthquake Data in Engineering Seismology: Predictive Models, Data Management and Networks. Geotechnical, Geological and Earthquake Engineering. Vol. 14. Springer. p. 194. ISBN 978-94-007-0151-9. Retrieved 2011-10-19.

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• Bath, M. (1979). Introduction to Seismology (Second, Revised ed.). Basel: Birkhäuser Basel. ISBN 9783034852838.
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• Ewing, W. M.; Jardetzky, W. S.; Press, F. (1957). Elastic Waves in Layered Media. McGraw-Hill Book Company.
• Gubbins, David (1990). Seismology and Plate Tectonics. Cambridge University Press. ISBN 978-0-521-37141-4.
• Hall, Stephen S. (2011). "Scientists on trial: At fault?". Nature. 477 (7364): 264–269. Bibcode:2011Natur.477..264H. doi:10.1038/477264a. PMID 21921895. S2CID 205067216.
• Kanamori, Hiroo (2003). (PDF). International Handbook of Earthquake and Engineering Seismology. Vol. 81B. International Association of Seismology & Physics of the Earth's Interior. pp. 1205–1216. Archived from the original (PDF) on 2013-10-24.
• Lay, Thorne, ed. (2009). Seismological Grand Challenges in Understanding Earth's Dynamic Systems (PDF). Report to the National Science Foundation, IRIS consortium.
• Schulte, Peter; Laia Alegret; Ignacio Arenillas; José A. Arz; Penny J. Barton; Paul R. Bown; Timothy J. Bralower; Gail L. Christeson; Philippe Claeys; Charles S. Cockell; Gareth S. Collins; Alexander Deutsch; Tamara J. Goldin; Kazuhisa Goto; José M. Grajales-Nishimura; Richard A. F. Grieve; Sean P. S. Gulick; Kirk R. Johnson; Wolfgang Kiessling; Christian Koeberl; David A. Kring; Kenneth G. MacLeod; Takafumi Matsui; Jay Melosh; Alessandro Montanari; Joanna V. Morgan; Clive R. Neal; Douglas J. Nichols; Richard D. Norris; Elisabetta Pierazzo; Greg Ravizza; Mario Rebolledo-Vieyra; Wolf Uwe Reimold; Eric Robin; Tobias Salge; Robert P. Speijer; Arthur R. Sweet; Jaime Urrutia-Fucugauchi; Vivi Vajda; Michael T. Whalen; Pi S. Willumsen (5 March 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary". Science. 327 (5970): 1214–1218. Bibcode:2010Sci...327.1214S. doi:10.1126/science.1177265. ISSN 1095-9203. PMID 20203042. S2CID 2659741. Retrieved 5 March 2010.
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• Wen, Lianxing; Helmberger, Donald V. (1998). "Ultra-Low Velocity Zones Near the Core-Mantle Boundary from Broadband PKP Precursors" (PDF). Science. 279 (5357): 1701–1703. Bibcode:1998Sci...279.1701W. doi:10.1126/science.279.5357.1701. PMID 9497284.

External links

 

Wikimedia Commons has media related to Seismology.

• European-Mediterranean Seismological Center, real-time earthquake information website.
• Seismological Society of America.
• Incorporated Research Institutions for Seismology.
• USGS Earthquake Hazards Program.
• A brief history of seismology to 1910 (UCSB ERI)