Seismology

Map of global tectonic activity.

Tungurahua Volcano 2011 (even active), July 2015. The Geophysical Institute, EPN monitors Tungurahua Volcano activity.

Sismogram.

seismology or seismology (from the Greek σεισμός (seismós) which means "earthquake&# 34; and λογία (logy), "study of") is a branch of geophysics that deals with the study of earthquakes and the propagation of elastic waves (seismic) that are generated in the interior and surface of the Earth, as well as tectonic plates. Studying the propagation of seismic waves includes determining the hypocenter (or focus), the location of the earthquake and the time that it has lasted. A phenomenon that is also of interest is the process of breaking rocks, since this is the cause of the release of seismic waves.

Its main objectives are:

• The study of the propagation of seismic waves within the Earth in order to know its internal structure;
• The study of the causes that give rise to the tremors;
• Prevention of seismic damage;
• Alert society about possible damages in the particular region.

Seismology includes, among other phenomena, the study of tidal waves and associated tidal waves (tsunamis) and vibrations prior to volcanic eruptions. In general, earthquakes originate at the limits of tectonic plates and are the product of the accumulation of tensions due to interactions between two or more plates. The tectonic plates (lithospheric plates) are a rigid structural unit, with a thickness of approximately 100 km, which constitutes the superficial spherical layer of the earth, according to the theory of plate tectonics (this theory explains the very particular distribution, in areas long and narrow, earthquakes, volcanoes and mountain ranges; likewise, the cause of continental drift).

The interpretation of the seismograms that are recorded by the passage of seismic waves allow us to study the interior of the earth. There are 3 types of seismic waves. The P and L waves (they produce Tsunamis) propagate across the globe, and the first, longitudinal and compression-decompression, do so in all media. S waves, transverse to the direction in which they propagate, are only transmitted in solid media.

History of seismology

This section is an extract from History of Seismology.[chuckles]edit]

Seismograph shown at the Tokyo Science Museum

Recorded representing the 1755 Lisbon earthquake

The study of earthquakes (or earthquakes or earthquakes) is as old as humanity itself. There are records written in China 3000 years ago, in which the impact of seismic shocks is described as we perceive them today. Japanese and Eastern European records with 1600 years old also describe in detail the effects of earthquakes on the population. In Central America and North America there are Maya and Aztec codexes, which refer to this natural phenomenon. In South America there was the flourishing of various civilizations and cultures that had known the earthquakes due to the type of sismorresistent architecture present from the Caral Civilization with the use of shicras, until the time of the incas that used a trapezoidal structure in their constructions. There are also documents from the colonial era (Indian Archives) that detailed the main events that affected American regions.

Academic interest in earthquakes also goes back to ancient times. The first speculations about its natural causes are attributed to Tales de Mileto (ca. 585 BC), Anaximenes de Mileto (ca. 550 BC), Aristotle (ca. 340 BC) and Zhang Heng, belonging to the Chinese Han dynasty, which in 132 BC. C. designed the first known seismograph.

In 1664, Athanasius Kircher proposed that earthquakes would be caused by the fire movement within a system of channels that would exist within the Earth. In 1703, Martin Lister (1638-1712) and Nicolás Lemery (1645-1715) proposed that earthquakes would be caused by chemical explosions within the Earth.

The 1755 Lisbon earthquake, which coincided with the general flourishing of science in Europe, triggered the scientific interest in understanding the behavior and cause of earthquakes. At that time John Bevis (1757) and above all John Michell (1761), which determined that the earthquakes were waves of movement caused by "mass of rock that move miles below the surface" of the Earth, was given.

From 1857, Robert Mallet founded instrumental seismology and carried out seismic experiments using explosives. He was also responsible for coining the word "seismology" (seismology).

In 1897 the theoretical calculations of Emil Wiechert predicted that the inner structure of the Earth would be made up of a mantle rich in silicates surrounding an iron-rich core.

In 1906 Richard Dixon Oldham identified the arrhbo separated from P waves, S waves and surface waves in the sismograms, and also found clear evidence that the Earth has a central core of a composition that is its own.

In 1910, after studying the earthquake in San Francisco in 1906, Harry Fielding Reid developed the theory of "Elastic Rebound", which remains the basis for modern tectonic studies. The advances that had then occurred both in mathematics and in physics (in the elastic behavior of the materials) were those that propitiated the development of the theory of the elastic rebound of Reid.

In 1926, Harold Jeffreys was the first to discover, based on his study on seismic waves, that the core of the Earth is in a liquid state. And in 1937, Danish math and sismologa Inge Lehmann determined that within that liquid core there was an internal core that was solid, while the outer core was liquid.

In the 1960s, the development of the theory of tectonic plates, a unifying theory of concepts in Earth Sciences, made it possible to understand the cause of earthquakes by placing them within a tectonic context.

Controlled seismic sources

Seismic waves produced by explosions or controlled vibratory sources are one of the main 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 geological traps in oil rocks, fault lines, rock types, and giant craters buried from meteorites for a long time. For example, the Chicxulub crater, which was caused by an impact that has been implicated in the extinction of the dinosaurs, was located in Central America by ejecta analysis at the Cretaceous-Paleogene boundary, and was later physically proven to exist using seismic maps. oil exploration.

Specialized texts

• Ailsa Allaby; Michael Allaby, eds (2003). Oxford Dictionary of Earth Sciences (Second edition). Oxford University Press.
• Ben-Menahem, Ari (1995), «A Concise History of Mainstream Seismology: Origins, Legacy, and Perspectives», Bulletin of the Seismological Society of America (Seismological Society of America) 85 (4): 1202-1225.
• 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 0-521-37141-4.
• Hall, Stephen S. (2011). «Scientists on trial: At fault?». Nature 477 (7364): 264-269. Bibcode:2011Natur.477..264H. PMID 21921895. doi:10.1038/477264a.
• Kanamori, Hiroo (2003). Earthquake prediction: An overview. International Handbook of Earthquake and Engineering Seismology. 81B. International Association of Seismology " Physics of the Earth's Interior. pp. 1205-1216. Archived from the original on 24 October 2013.
• Lay, Thorne, ed. (2009). Seismological Grand Challenges in Understanding Earth's Dynamic Systems. Report to the National Science Foundation, IRIS consortium.
• 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 Good, José M. Grajales-Nishimura, Richard A. F. «The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary». Science (AAAS) 327 (5970): 1214-1218. Bibcode:2010Sci...327.1214S. ISSN 1095-9203. PMID 20203042. doi:10.1126/science.1177265. Consultation on 5 March 2010. The reference uses the obsolete parameter |coautores= (help)
• Shearer, Peter M. (2009). Introduction to Seismology (Second edition). Cambridge University Press. ISBN 978-0-521-70842-5.
• Stein, Seth; Wysession, Michael (2002). An Introduction to Seismology, Earthquakes and Earth Structure. Wiley-Blackwell. ISBN 978-0-86542-078-6.
• Wen, Lianxing; Helmberger, Donald V. (1998). «Ultra-Low Velocity Zones Near the Core-Mantle Boundary from Broadband PKP Precursors». Science 279 (5357): 1701-1703. Bibcode:1998Sci...279.1701W. doi:10.1126/science.279.5357.1701.