Английская Википедия:Depth of focus (tectonics)
Шаблон:Distinguish In seismology, the depth of focus or focal depth is the depth at which an earthquake occurs. Earthquakes occurring at a depth of less than Шаблон:Convert are classified as shallow-focus earthquakes, while those with a focal depth between Шаблон:Convert and Шаблон:Convert are commonly termed mid-focus or intermediate-depth earthquakes.[1] In subduction zones, where older and colder oceanic crust sinks under another tectonic plate, deep-focus earthquakes may occur at much greater depths in the mantle, ranging from Шаблон:Convert up to Шаблон:Convert.[2][3]
The cause of deep-focus earthquakes is still not entirely understood since subducted lithosphere at that pressure and temperature regime should not exhibit brittle behavior. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure,[4] with which they are believed to be associated. Earthquakes at this depth of focus typically occur at oceanic-continental convergent boundaries, along Wadati–Benioff zones.[5]
Discovery
The evidence for deep-focus earthquakes was discovered in 1922 by H.H. Turner of Oxford, England. Previously, all earthquakes were considered to have shallow focal depths. The existence of deep-focus earthquakes was confirmed in 1931 from studies of the seismograms of several earthquakes, which in turn led to the construction of travel-time curves for intermediate and deep earthquakes.[6]
See also
References
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Шаблон:Tectonics-stub
- ↑ Spence, William, Stuart A. Sipkin, and George L. Choy (1989). "Measuring the Size of an Earthquake." Earthquake Information Bulletin (USGS). 21 (1), 58–63.
- ↑ Шаблон:Cite web
- ↑ Шаблон:Cite web
- ↑ Шаблон:Cite journal
- ↑ Marius Vassiliou, Bradford Hager, and Arthur Raefsky (1984): "The Distribution of Earthquakes with Depth and Stresses in Subducting Slabs", Journal of Geodynamics 1, 11–28.
- ↑ Spence, William, Stuart A. Sipkin, and George L. Choy (1989). Шаблон:USGS Earthquake Information Bulletin (USGS). 21 (1), 58–63.