低速區

低速區（LVZ）是上地幔接近岩石圈與軟流圈邊界處，地震波橫波速度顯著偏低、電導率顯著偏高的區域。深度從80km至300km。其中部分區域的地震波縱波缺失。^[2]^[2]^[3]^[4]

另外一個地震波速顯著降低的區域在核幔邊界的不超過50km的薄層，稱為超低速區（英語：Ultra low velocity zone）（ULVZ）。^[3]

低速區可以用部分熔融（約1%）解釋。^[2]水可以降低熔點，扮演了重要角色。^[4]^[5]

地震波的橫波在低速區下降了3–6%，比縱波波速變化更顯著。^[7]雷氏不連續面是低速區的下界。

只需要0.05–0.1 %的水就可導致1%的熔融，產生低速區。地盾下缺乏低速區可解釋為地熱梯度太小，阻止了部分熔融。^[8]

識別

低速區的存在最早是由賓諾·古登堡 (Beno Gutenberg) 在1959年觀察到地震波到達速度比預期慢時提出的。^[9] 他指出，在距震中 1° 到 15° 之間，縱向到達的振幅呈指數下降，之後突然大幅增加。低速區的存在使地震能量散焦，隨後是高速梯度使其集中，這為這些觀察結果提供了解釋。^[10]

參見

參考文獻

^ GR Helffrich & BJ Wood. The Earth's Mantle (PDF). Nature (Macmillan Magazines). 2002, 412 (2 August): 501; Figure 1. doi:10.1038/35087500. ^{[失效連結]}
^ ^2.0 ^2.1 ^2.2 L Stixrude & C Lithgow-Bertolloni. Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone (PDF). Journal of Geophysical Research. 2005, 110: B03204 [2018-12-16]. Bibcode:2005JGRB..11003204S. doi:10.1029/2004JB002965. （原始內容 (PDF)存檔於2011-08-30）.
^ ^3.0 ^3.1 EJ Garnero, MS Thorne, A McNamara & S Rost. Chapter 6: Fine-scale ultra-low-velocity zone layering at the core-mantle boundary and superplumes. David A Yuen; Shigenori Maruyama (編). Superplumes: beyond plate tectonics. Springer. 2007: 139. ISBN 1-4020-5749-0.
^ ^4.0 ^4.1 Philip Kearey; Keith A. Klepeis; Frederick J. Vine. Global tectonics 3rd. Wiley-Blackwell. 2009: 32. ISBN 1-4051-0777-4.
^ It is hypothesized that the absence of plate tectonics on the planet Venus is due to the absence of water in its crust and upper mantle. Cooling occurs largely through mantle plumes. See Gillian R. Foulger. Plates, plumes, and paradigms; Volume 388 of Special papers. Geological Society of America. 2005: 857. ISBN 0-8137-2388-4.
^ Figure patterned after Don L Anderson. New theory of the earth 2nd. Cambridge University Press. 2007: 102, Figure 8.6. ISBN 0-521-84959-4. ; Original figure attributed to Grand & Helmberger (1984)
^ Brown, G.C.; Mussett A.E. The inaccessible earth. Taylor & Francis. 1981: 235 [2010-02-20]. ISBN 978-0-04-550028-4.
^ Condie, K.C. Plate tectonics and crustal evolution. Butterworth-Heinemann. 1997: 282 [2010-02-20]. ISBN 978-0-7506-3386-4.
^ Gutenberg, B. Physics of the Earth's Interior. New York: Academic Press. 1959: 240. ISBN 0-12-310650-8.
^ Anderson, D.L. 3. The Crust and Upper Mantle. Theory of the Earth (PDF). Boston: Blackwell Scientific Publications. 1989 [2010-02-20]. ISBN 0-521-84959-4. （原始內容 (PDF)存檔於2010-06-23）.

[Helffrich-1] GR Helffrich & BJ Wood. The Earth's Mantle (PDF). Nature (Macmillan Magazines). 2002, 412 (2 August): 501; Figure 1. doi:10.1038/35087500. ^{[失效連結]}

[Stixrude-2] 2.0 ^2.1 ^2.2 L Stixrude & C Lithgow-Bertolloni. Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone (PDF). Journal of Geophysical Research. 2005, 110: B03204 [2018-12-16]. Bibcode:2005JGRB..11003204S. doi:10.1029/2004JB002965. （原始內容 (PDF)存檔於2011-08-30）.

[Rost-3] 3.0 ^3.1 EJ Garnero, MS Thorne, A McNamara & S Rost. Chapter 6: Fine-scale ultra-low-velocity zone layering at the core-mantle boundary and superplumes. David A Yuen; Shigenori Maruyama (編). Superplumes: beyond plate tectonics. Springer. 2007: 139. ISBN 1-4020-5749-0.

[Vine-4] 4.0 ^4.1 Philip Kearey; Keith A. Klepeis; Frederick J. Vine. Global tectonics 3rd. Wiley-Blackwell. 2009: 32. ISBN 1-4051-0777-4.

[Venus-5] It is hypothesized that the absence of plate tectonics on the planet Venus is due to the absence of water in its crust and upper mantle. Cooling occurs largely through mantle plumes. See Gillian R. Foulger. Plates, plumes, and paradigms; Volume 388 of Special papers. Geological Society of America. 2005: 857. ISBN 0-8137-2388-4.

[Anderson1-6] Figure patterned after Don L Anderson. New theory of the earth 2nd. Cambridge University Press. 2007: 102, Figure 8.6. ISBN 0-521-84959-4. ; Original figure attributed to Grand & Helmberger (1984)

[Brown-7] Brown, G.C.; Mussett A.E. The inaccessible earth. Taylor & Francis. 1981: 235 [2010-02-20]. ISBN 978-0-04-550028-4.

[Condie-8] Condie, K.C. Plate tectonics and crustal evolution. Butterworth-Heinemann. 1997: 282 [2010-02-20]. ISBN 978-0-7506-3386-4.

[Bruno-9] Gutenberg, B. Physics of the Earth's Interior. New York: Academic Press. 1959: 240. ISBN 0-12-310650-8.

[Don-10] Anderson, D.L. 3. The Crust and Upper Mantle. Theory of the Earth (PDF). Boston: Blackwell Scientific Publications. 1989 [2010-02-20]. ISBN 0-521-84959-4. （原始內容 (PDF)存檔於2010-06-23）.

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