AskDefine | Define asthenosphere

Dictionary Definition

asthenosphere n : the lower layer of the crust

User Contributed Dictionary

English

Noun

asthenosphere
  1. the zone of the Earth's upper mantle, below the lithosphere

Translations

the zone of the Earth's upper mantle, below the lithosphere
  • French: asthénosphère

Extensive Definition

The asthenosphere (from an invented Greek a + 'sthenos "without strength") is the region of the Earth between 100 and 200 km (~ 62 and 124 miles) below the surface — but perhaps extending as deep as 400 km (~ 249 miles) — that is the weak or "soft" zone in the upper mantle. It lies just below the lithosphere, which is involved in plate movements and isostatic adjustments. In spite of its heat, pressures keep it plastic, and it has a relatively low density. Seismic waves, the speed of which decrease with decreasing rigidity of a medium, pass relatively slowly through the asthenosphere, the cue that originally alerted seismologists to its presence; thus it has been given the name low-velocity zone.
Under the thin oceanic plates the asthenosphere is usually much nearer the seafloor surface, and at mid-ocean ridges it rises to within a few kilometres of the ocean floor.
The upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of the Earth's crust move about. Due to the temperature and pressure conditions in the asthenosphere, rock becomes ductile, moving at rates of deformation measured in cm/yr over lineal distances eventually measuring thousands of kilometers. In this way, it flows like a convection current, radiating heat outward from the Earth's interior. Above the asthenosphere, at the same rate of deformation, rock behaves elastically and, being brittle, can break, causing faults. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere, creating the movement of crustal plates described by Plate tectonics theory.
Although its presence was suspected as early as 1926, the worldwide occurrence of the asthenosphere was confirmed by analyses of earthquake waves from the Great Chilean Earthquake of May 22, 1960.

External links

References

  • Donald L. Turcotte and Gerlad Schubert. Geodynamics, 2nd ed., Cambridge University Press 2001
asthenosphere in Belarusian (Tarashkevitsa): Астэнасфэра
asthenosphere in Bulgarian: Астеносфера
asthenosphere in Catalan: Astenosfera
asthenosphere in Czech: Astenosféra
asthenosphere in Danish: Asthenosfære
asthenosphere in German: Asthenosphäre
asthenosphere in Estonian: Astenosfäär
asthenosphere in Modern Greek (1453-): Ασθενόσφαιρα
asthenosphere in Spanish: Astenosfera
asthenosphere in Esperanto: Astenosfero
asthenosphere in French: Asthénosphère
asthenosphere in Galician: Astenosfera
asthenosphere in Korean: 연약권
asthenosphere in Croatian: Astenosfera
asthenosphere in Italian: Astenosfera
asthenosphere in Latvian: Astenosfēra
asthenosphere in Lithuanian: Astenosfera
asthenosphere in Hungarian: Asztenoszféra
asthenosphere in Dutch: Asthenosfeer
asthenosphere in Japanese: アセノスフェア
asthenosphere in Norwegian: Astenosfære
asthenosphere in Polish: Astenosfera
asthenosphere in Portuguese: Astenosfera
asthenosphere in Russian: Астеносфера
asthenosphere in Simple English: Asthenosphere
asthenosphere in Slovak: Astenosféra
asthenosphere in Slovenian: Astenosfera
asthenosphere in Finnish: Astenosfääri
asthenosphere in Swedish: Astenosfär
asthenosphere in Vietnamese: Quyển astheno
asthenosphere in Ukrainian: Астеносфера
asthenosphere in Venetian: Astenosfera
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