翻訳と辞書 |
Depth of focus (tectonics) : ウィキペディア英語版 | Depth of focus (tectonics) In seismology, the depth of focus or focal depth refers to the depth at which an earthquake occurs. Earthquakes occurring at a depth of less than are classified as shallow-focus earthquakes, while those with a focal depth between and are commonly termed mid-focus or intermediate-depth earthquakes.〔D. Armstrong, F. Mugglestone, R. Richards and F. Stratton, ''OCR AS and A2 Geology,'' Pearson Education Limited, 2008, p. 32 ISBN 978-0-435-69211-7〕 In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths in the mantle, ranging from up to .〔(【引用サイトリンク】title=M7.5 Northern Peru Earthquake of 26 September 2005 )〕 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, 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.〔Marius Vassiliou, Bradford Hager, and Arthur Raefsky (1984): "The Distribution of Earthquakes with Depth and Stresses in Subducting Slabs", J. of Geodynamics 1, 11–28.〕 ==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.
抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Depth of focus (tectonics)」の詳細全文を読む
スポンサード リンク
翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|