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Topic: Asthenosphere

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	Earth's Crust, Lithosphere and Asthenosphere
		These puzzle pieces move a little bit each year as they slide on top of a somewhat fluid part of the mantle called the asthenosphere.
		The asthenosphere is solid even though it is at very hot temperatures of about 1600 C due to the high pressures from above.
		The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back.
	www.windows.ucar.edu /tour/link=/earth/interior/earths_crust.html&edu=high (305 words)

	asthenosphere - HighBeam Encyclopedia (Site not responding. Last check: )
		asthenosphere, 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 lithosphere.
		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 tectonics).
		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.
	www.encyclopedia.com /doc/1E1-asthenos.html (421 words)

	asthenosphere - Search Results - MSN Encarta
		Asthenosphere, hot, partially molten layer of Earth, lying below the lithosphere (the rocky outer layer of Earth).
		Earthquake : causes of earthquakes : shifting of the lithosphere on the asthenosphere: Lithosphere
		Earth scientists distinguished the lithosphere from the underlying asthenosphere by studying seismic waves.
	encarta.msn.com /asthenosphere.html (126 words)

	Asthenosphere
		The asthenosphere (from the Greek asthenia, "weakness") is the region of the Earth between 100-200 km below the surface, but may extend as deep as 400 km.
		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.
		Although its presence was suspected as early as 1926, the worldwide occurrence of the asthenosphere was confirmed by analyses of earthquake waves from the Chilean Great earthquake of May 22, 1960.
	www.xasa.com /wiki/en/wikipedia/a/as/asthenosphere.html (260 words)

	Asthenosphere Summary
		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.
		Although its presence was suspected as early as 1926, the worldwide occurrence of the asthenosphere was confirmed by analyses of earthquake waves from the Chilean Great earthquake of May 22, 1960.
	www.bookrags.com /Asthenosphere (1386 words)

	University of Toronto GeoTec Lab
		The aim is to investigate the relations between the mantle (asthenospheric) flow and the subducting lithosphere.
		The asthenosphere is made of low viscosity (56 Pa.s) pure silicon while the lithopheric plates are made of granular filler and silicon mixtures (2.7E4 Pa.s) which densities can be equal or slightly higher than the density of the asthenosphere.
		Experiment 2: The lithosphere is neutrally buoyant (its density equals the density of the asthenosphere) and the subduction occurs near the middle of the tank length where the asthenospheric flow is sub-horizontal to the left.
	www.geology.utoronto.ca /tectonicslab/Subduction.html (507 words)

	The Dispatch - Serving the Lexington, NC - News (Site not responding. Last check: )
		The asthenosphere (from an invented Greek a + sthenos "without strength") is the region of the Earth between 100-200 km below the surface — but perhaps extending as deep as 400 km — that is the weak or "soft" zone in the upper mantle.
		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.
		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.
	www.the-dispatch.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=asthenosphere (320 words)

	Asthenosphere: Free Encyclopedia Articles at Questia.com Online Library
		The asthenosphere is generally located between 45U+2013155 miles (72U+2013250 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.
		ASTHENOSPHERE asthen sfer, region in the upper mantle of the...the overlying lithosphere.
		Basaltic magma is derived by partial melting of the peridotite that is found in the asthenosphere which reaches the mid-ocean ridges, such as the Mid-Atlantic Ridge, and forms the new oceanic crust, the uppermost layer...
	www.questia.com /library/encyclopedia/101230327 (797 words)

	Asthenosphere: World of Earth Science
		It was first named in 1914 by the British geologist J. Barrell, who divided Earth's overall structure into three major sections: the lithosphere, or outer layer of rock-like material; the asthenosphere; and the centrosphere, or central part of the planet.
		The asthenosphere gets its name from the Greek word for weak, asthenis, because of the relatively fragile nature of the materials of which it is made.
		The asthenosphere is now thought to play a critical role in the movement of plates across the face of Earth's surface.
	science.enotes.com /earth-science/asthenosphere (1082 words)

	homework help: i need to creat a poster of the earth’s layers. - Help.com
		The asthenosphere (from an invented Greek ἀσθενός a + ''sthenos "without strength") is the region of the Earth between 100-200 km below the surface — but perhaps extending as deep as 400 km — that is the weak or "soft" zone in the upper mantle.
		Seismic waves, the speed of which decrease with the softness 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.
		The continental crust is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves.
	help.com /post/27344-i-need-to-creat-a-poster-of-the-ear (1417 words)

	asthenosphere — Infoplease.com
		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.
		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.
	www.infoplease.com /ce6/sci/A0805111.html (0 words)

	Lithosphere
		The terms lithosphere and asthenosphere predate plate tectonics by about 50 years, and they were ready-made for their application to plate tectonics.
		In terms of a conceptual model, the asthenosphere behaves like glacial ice, brittle and solid on a short time scale, but flowing over time, compared with the lithosphere which is like rock at the surface, essentially solid and strong over all time scales.
		The asthenosphere is less dense than the mantle lithosphere, and therefor a root of mantle lithosphere extending down into the asthenosphere causes a positive load (more dense lithosphere replacing less dense asthenosphere) and adds to the topographic load rather than compensating it.
	www.es.mq.edu.au /courses/GEOS260/Lithosphere1.html (1830 words)

	Brainboost - asthenosphere (Site not responding. Last check: )
		We know that the asthenosphere is a solid because S waves can travel through it, but we also know that it can flow because the plates are moving about without any earthquakes at their bases and at oceanic trenches, oceanic plates actually sink into the asthenosphere.
		One is that only the very top level of the asthenosphere is moving, and that is causing the plates to move.
		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.
	www.brainboost.com /search.asp?Q=asthenosphere&lfmq=1 (206 words)

	Continental delamination (Site not responding. Last check: )
		Continental lithosphere is in unstable mechanical equilibrium because its mantle layer is denser than the asthenosphere.
		If any process such as cracking, slumping, or plume erosion initially provided an elongated conduit connecting the underlying asthenosphere with the base of the continental crust, the dense lithospheric boundary layer could peel away from the crust and sink.
		A new mantle lithosphere is gradually formed by cooling of asthenosphere.
	element.ess.ucla.edu /publications/1979_delamination/1979_delamination.htm (675 words)

	05-005 (Lithosphere-Asthenosphere Boundary)
		In the latest issue of Nature, a trio of geophysicists from Brown University and the Massachusetts Institute of Technology publish research that sheds new light on the nature of the boundary between these rocky regions.
		Lead author Catherine Rychert, a 26-year-old graduate student in Brown’s Department of Geological Sciences, found a sharp dividing line between the lithosphere and the asthenosphere, according to data culled from seismic sensors sprinkled across the northeastern United States and southeastern Canada.
		Rychert said that water or a small amount of partly molten rock must also be present in the asthenosphere to cause such an abrupt change in the mechanical strength of the rock.
	www.brown.edu /Administration/News_Bureau/2005-06/05-005.html (536 words)

	2D Lateral Heterogeneity 1
		Lateral variations in asthenospheric viscosity in model LV2 result in an uplift curve similar to the one of model L01, while an additional lateral variation in lithospheric thickness in model LV3 shifts the land uplift towards that for model L02 for times before 6 ka BP.
		Upon the introduction of a laterally variable asthenospheric viscosity (model LV2), the minimum in horizontal displacement is shifted about 150 km closer to the load center, together with a slight increase in amplitude.
		If asthenospheric viscosity beneath the center of the load is allowed to decrease as in model LV4, then the minimum in horizontal displacement decreases in amplitude by a factor of 2/3.
	www.geo.ucalgary.ca /~wu/2DLatHet1.html (1510 words)

	Plate Tectonics
		On top of the asthenosphere there is a rigid layer of solid rocks called the lithosphere, formed by the uppermost mantle and the crust.
		Their explanation for the symmetric patterns is as follows: basaltic magma rises from the asthenosphere and is extruded along central fissures at the MORs.
		Later, a new batch of basalt from the asthenosphere fractures the previous one, pushes it toowards the sides, and crystallizes in the center of the MOR.
	mapatino.myweb.uga.edu /Pltect3.htm (3163 words)

	04.17.2003 - Continental roots go deep, but not as deep as some people thought
		Their interpretation of seismic data resolves a debate within the geophysical community about the depth of the boundary between the rigid lithosphere that floats on the Earth's surface and the hot convecting mantle that underlies it.
		The asthenosphere, the very top of the mantle, can be detected because of its anisotropy - horizontally polarized shear waves generated by earthquakes travel faster through this rock than vertically polarized seismic waves.
		"Somehow the asthenosphere needs to be sustained over geological times, and I think that heat is being pumped from below and is actively keeping the asthenosphere less viscous and more deformable," she said, and thus able to move the lithosphere around.
	www.berkeley.edu /news/media/releases/2003/04/17_roots.shtml (621 words)

	Present-Day Crustal Movements: Lithosphere Models
		Note that in the context of these two models, the terms "lithosphere" and "asthenosphere" are linked to mechanical properties of the Earth's crust and upper mantle: The lithosphere is the strong elastic layer near the Earth's surface, and the asthenosphere is the region of ductile flow that lies beneath.
		Thus considered, the boundary between "lithosphere" and "asthenosphere" defines the zone of decoupling between surface tectonic processes and those that occur in the ductile region beneath.
		Similarly, except for the transition from elastic lithosphere to viscoelastic asthenosphere, depth variations in material properties are not considered, although, again, solutions have been obtained for faulting in plane-layered elastic and viscoelastic media.
	www.johnmartin.com /earthquakes/eqsafs/safs_745.htm (1462 words)

	Information about Earth's Layers
		Heat and pressure cause a small amount of melting to occur in the asthenosphere.
		Since the asthenosphere is more liquid than the rest of the mantle, the broken lithosphere plates are able to "float" on it.
		When the material in the asthenosphere is heated, it becomes less dense and rises.
	www.usoe.k12.ut.us /curr/science/sciber00/7th/earth/sciber/erlayers.htm (541 words)

	Temperature from sedimentary successions
		The emplacement and dispersal of hot asthenosphere is predicted to cause faster subsidence of hotspot crust compared to that seen in normal oceanic crust.
		Isolating the effect of hot asthenosphere on plate subsidence is simplest if the crust was emplaced close to the crest of a mid-ocean ridge, as this allows a simple comparison of the subsidence reconstructed from the sedimentary record with that of normal oceanic crust.
		The main remaining question, then, is whether the asthenosphere is close to the melting point or whether it is so cold and uniform that deep heat and material is required to melt it and replenish it, as in the plume hypothesis.
	www.mantleplumes.org /SedTemp.html (5216 words)

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