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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
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When seismic data is too scarce to calculate a focal depth, a "fixed depth" is assigned. For example, many earthquakes occurring in oceans are assigned fixed depth because of limited local seismic records. The United States
Geological Survey presently determines 10 km (6.2 mi) to be the
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occurs. Earthquakes occurring at a depth of less than 70 km (43 mi) are classified as shallow-focus earthquakes, while those with a focal depth between 70 km (43 mi) and 300 km (190 mi) are commonly termed mid-focus or intermediate-depth earthquakes. In
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fixed depth for most shallow earthquakes as their actual focal depth is usually close to that value. Many earthquakes in their catalogue are assigned 10 km (6.2 mi) depth. The previous fixed depth used by the agency was 33 km (21 mi).
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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
310:"A new method to determine the depth of earthquakes on oceanic transform faults using teleseismic arrays: application to the Chain transform, equatorial Atlantic"
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Marius
Vassiliou, Bradford Hager, and Arthur Raefsky (1984): "The Distribution of Earthquakes with Depth and Stresses in Subducting Slabs",
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structure, with which they are believed to be associated. Earthquakes at this depth of focus typically occur at oceanic-continental
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may occur at much greater depths in the mantle, ranging from 300 km (190 mi) up to 700 km (430 mi).
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Greene II, H. W.; Burnley, P. C. (October 26, 1989). "A new self-organizing mechanism for deep-focus earthquakes".
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turn led to the construction of travel-time curves for intermediate and deep earthquakes.
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The cause of deep-focus earthquakes is still not entirely understood since subducted
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AGU Fall
Meeting 2022, held in Chicago, IL, 12-16, id. T44A-04
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Spence, William, Stuart A. Sipkin, and George L. Choy (1989).
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Spence, William, Stuart A. Sipkin, and George L. Choy (1989).
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Hongjian, Fang; Abercrombie, Rachel E. (December 2022).
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330:. United States Geological Survey
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255:Journal of Geodynamics
54:deep-focus earthquakes
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81:Wadati–Benioff zones
478:Types of earthquake
225:1989Natur.341..733G
116:Focus (earthquake)
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467:Categories
363:seismology
197:2008-08-01
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127:References
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