asthenosphere

enUK

as·then·o·sphere

A0482000 (ăs-thĕn′ə-sfîr′)n. A zone of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock.

[Greek asthenēs, weak; see asthenia + sphere.]

asthenosphere

(əsˈθiːnəˌsfɪə; -ˈθɛn-) n (Geological Science) a thin semifluid layer of the earth (100–200 km thick), below the outer rigid lithosphere, forming part of the mantle and thought to be able to flow vertically and horizontally, enabling sections of lithosphere to subside, rise, and undergo lateral movement. See also isostasy[C20: from astheno-, from Greek asthenēs weak + sphere]

as•then•o•sphere

(æsˈθɛn əˌsfɪər)

n. the region below the lithosphere where rock is less rigid than that above and below it. [1910–15; < Greek asthen(ḗs) frail (see asthenia) + -o- + -sphere]

as·then·o·sphere

(ăs-thĕn′ə-sfîr′) The upper part of the Earth's mantle. The asthenosphere lies beneath the lithosphere and consists of several hundred miles of partially molten rock. Because it is partially molten, seismic waves passing through this layer have slow velocities. Compare atmosphere, hydrosphere, lithosphere.

asthenosphere

A dense, plastic layer of mantle below the lithosphere.

Thesaurus

Noun

asthenosphere - the lower layer of the crust layer - a relatively thin sheetlike expanse or region lying over or under anothercrust, Earth's crust - the outer layer of the Earth

Translations

asthenosphere

enUK

asthenosphere

(ăsthēn`əsfēr), region in the upper mantle of the earth's interior, characterized by low-density, semiplastic (or partially molten) rock material chemically similar to the overlying lithospherelithosphere
, brittle uppermost shell of the earth, broken into a number of tectonic plates. The lithosphere consists of the heavy oceanic and lighter continental crusts, and the uppermost portion of the mantle.
..... Click the link for more information. . 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 (see plate tectonicsplate tectonics,
theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history.
..... Click the link for more information. ). The asthenosphere is generally located between 45–155 miles (72–250 km) beneath the earth's surface, though under the oceans it is usually much nearer the surface and at mid-ocean ridges rises to within a few miles of the ocean floor. Although its presence was suspected as early as 1926, the worldwide occurrence of the plastic zone was confirmed by analyses of earthquake waves from the Chilean earthquake of May 22, 1960. The seismic waves, the speed of which decreases with the softness of the medium, passed relatively slowly though the asthenosphere, thus it was given the name Low Velocity zone, or the Seismic Wave Guide (see seismologyseismology
, scientific study of earthquakes and related phenomena, including the propagation of waves and shocks on or within the earth by natural or artificially generated seismic signals.
..... Click the link for more information. ). Deep-zone earthquakes, i.e., those that occur in the asthenosphere or below it, may be caused by crustal plates sinking into the mantle along convergent crustal boundaries. See earthearth,
in geology and astronomy, 3rd planet of the solar system and the 5th largest, the only planet definitely known to support life. Gravitational forces have molded the earth, like all celestial bodies, into a spherical shape.
..... Click the link for more information. .

asthenosphere

(ass-th'en -ŏ-sfeer) See Earth.

Asthenosphere

a layer of low hardness, strength, and viscosity in the earth’s upper mantle. It is identical to Gutenberg’s layer. It is found at depths of about 100 km under the continents and about 50 km under the ocean floor; the lower boundary occurs at 250 to 350 km. The layer may not be continuous. Seismic studies have shown that the rate of propagation of transverse and possibly longitudinal seismic waves within the asthenosphere is somewhat slower than in the covering and underlying layers of the upper mantle. The viscosity of the substance of the asthenosphere is 10¹⁹ to 10²³ poises, whereas below and above the boundaries of the asthenosphere it is at least 10²³ poises. It is conjectured that there is a slow overflow of masses in a horizontal direction within the asthenosphere because of the low yield point. The overflow is caused by uneven stress from the earth’s crust.

The presence of the asthenosphere is explained by the high geothermal gradient, the high temperature of the substance of the asthenosphere (close to the melting point), and processes of relaxation. Volcanic materials usually originate in the asthenosphere, and the subcrustal masses that accomany the main tectonic processes are displaced. The term “asthenosphere” was introduced in 1914 by the American geologist J. Barrell.

V. A. MAGNITSKII

asthenosphere

[as′then·ə‚sfir] (geology) That portion of the upper mantle beneath the rigid lithosphere which is plastic enough for rock flowage to occur; extends from a depth of 30-60 miles (50-100 kilometers) to about 240 miles (400 kilometers) and is seismically equivalent to the low velocity zone.

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Words related to asthenosphere

noun the lower layer of the crust

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