Asthenosphere

<div dir="ltr" style="text-align: left;" trbidi="on"> <br /> <br /> <br /> <h1 class="firstHeading" id="firstHeading" lang="en" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; border-bottom: 1px solid rgb(162, 169, 177); font-family: "Linux Libertine", Georgia, Times, serif; font-size: 1.8em; font-weight: normal; line-height: 1.3; margin: 0px 0px 0.25em; overflow: visible; padding: 0px;"> Asthenosphere</h1> <div class="mw-body-content" id="bodyContent" style="color: #222222; font-family: sans-serif; font-size: 0.875em; line-height: 1.6; position: relative; z-index: 0;"> <div class="noprint" id="siteSub" style="font-size: 12.88px;"> From Wikipedia, the free encyclopedia</div> <div id="contentSub" style="color: #54595d; font-size: 11.76px; line-height: 1.2em; margin: 0px 0px 1.4em 1em; width: auto;"> </div> <div id="jump-to-nav"> </div> <a class="mw-jump-link" href="https://en.wikipedia.org/wiki/Asthenosphere#mw-head" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; border: 0px; clip: rect(1px, 1px, 1px, 1px); color: #0b0080; display: block; height: 1px; margin: -1px; overflow: hidden; padding: 0px; position: absolute !important; text-decoration-line: none; width: 1px;">Jump to navigation</a><a class="mw-jump-link" href="https://en.wikipedia.org/wiki/Asthenosphere#p-search" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; border: 0px; clip: rect(1px, 1px, 1px, 1px); color: #0b0080; display: block; height: 1px; margin: -1px; overflow: hidden; padding: 0px; position: absolute !important; text-decoration-line: none; width: 1px;">Jump to search</a><br /> <div class="mw-content-ltr" dir="ltr" id="mw-content-text" lang="en" style="direction: ltr;"> <div class="mw-parser-output"> <div class="thumb tright" style="clear: right; float: right; margin: 0.5em 0px 1.3em 1.4em; width: auto;"> <div class="thumbinner" style="background-color: #f8f9fa; border: 1px solid rgb(200, 204, 209); font-size: 13.16px; min-width: 100px; overflow: hidden; padding: 3px; text-align: center; width: 352px;"> <a class="image" href="https://en.wikipedia.org/wiki/File:Subduction-en.svg" style="background: none; color: #0b0080; text-decoration-line: none;"><img alt="" class="thumbimage" data-file-height="854" data-file-width="1482" decoding="async" height="202" src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Subduction-en.svg/350px-Subduction-en.svg.png" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Subduction-en.svg/525px-Subduction-en.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Subduction-en.svg/700px-Subduction-en.svg.png 2x" style="background-color: white; border: 1px solid rgb(200, 204, 209); vertical-align: middle;" width="350" /></a><br /> <div class="thumbcaption" style="border: 0px; font-size: 12.3704px; line-height: 1.4em; padding: 3px; text-align: left;"> <div class="magnify" style="float: right; margin-left: 3px; margin-right: 0px;"> <a class="internal" href="https://en.wikipedia.org/wiki/File:Subduction-en.svg" style="background: linear-gradient(transparent, transparent), url("/w/resources/src/mediawiki.skinning/images/magnify-clip-ltr.svg?8330e"); color: #0b0080; display: block; height: 11px; overflow: hidden; text-decoration-line: none; text-indent: 15px; user-select: none; white-space: nowrap; width: 15px;" title="Enlarge"></a></div> The asthenosphere shown at a <a href="https://en.wikipedia.org/wiki/Subduction" style="background: none; color: #0b0080; text-decoration-line: none;" title="Subduction">subduction</a> boundary</div> </div> </div> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> The <b>asthenosphere</b> (from <a href="https://en.wikipedia.org/wiki/Greek_language" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Greek language">Greek</a> ἀσθενής <i>asthenḗs</i> 'weak' + "sphere") is the highly <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Viscous" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Viscous">viscous</a>, mechanically weak<sup class="reference" id="cite_ref-1" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-1" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[1]</a></sup> and <a href="https://en.wikipedia.org/wiki/Ductility_(Earth_science)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Ductility (Earth science)">ductile</a> region of the <a href="https://en.wikipedia.org/wiki/Upper_mantle_(Earth)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Upper mantle (Earth)">upper mantle</a> of the <a href="https://en.wikipedia.org/wiki/Earth" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Earth">Earth</a>. It lies below the <a href="https://en.wikipedia.org/wiki/Lithosphere" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Lithosphere">lithosphere</a>, at depths between approximately 80 and 200 km (50 and 120 miles) below the surface. The <a href="https://en.wikipedia.org/wiki/Lithosphere%E2%80%93asthenosphere_boundary" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Lithosphere–asthenosphere boundary">lithosphere–asthenosphere boundary</a> is usually referred to as LAB.<sup class="reference" id="cite_ref-2" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-2" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[2]</a></sup><sup class="reference" id="cite_ref-3" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-3" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[3]</a></sup> The asthenosphere is almost solid, although some of its regions could be molten (e.g., below <a href="https://en.wikipedia.org/wiki/Mid-ocean_ridge" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Mid-ocean ridge">mid-ocean ridges</a>). The lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature. However, the <a href="https://en.wikipedia.org/wiki/Rheology" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Rheology">rheology</a> of the asthenosphere also depends on the rate of deformation,<sup class="reference" id="cite_ref-4" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-4" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[4]</a></sup>which suggests that the asthenosphere could be also formed as a result of a high rate of deformation. In some regions the asthenosphere could extend as deep as 700 km (430 mi). It is considered the source region of mid-ocean ridge <a href="https://en.wikipedia.org/wiki/Basalt" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Basalt">basalt</a> (MORB).<sup class="reference" id="cite_ref-5" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-5" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[5]</a></sup></div> <div class="toc" id="toc" style="background-color: #f8f9fa; border: 1px solid rgb(162, 169, 177); display: table; font-size: 13.3px; padding: 7px;"> <input class="toctogglecheckbox" id="toctogglecheckbox" role="button" style="direction: ltr; display: none; opacity: 0; position: absolute; z-index: -1;" type="checkbox" /><br /> <div class="toctitle" dir="ltr" lang="en" style="direction: ltr; text-align: center;"> <h2 style="background: none; border: 0px; color: black; display: inline; font-size: 13.3px; line-height: 1.3; margin: 1em 0px 0.25em; overflow: hidden; padding: 0px;"> Contents</h2> <span class="toctogglespan" style="font-size: 12.502px;"><label class="toctogglelabel" for="toctogglecheckbox" style="color: #0645ad; cursor: pointer;"></label></span></div> <ul style="list-style-image: none; list-style-type: none; margin: 0.3em 0px; padding: 0px;"> <li class="toclevel-1 tocsection-1" style="margin-bottom: 0.1em;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#Characteristics" style="background: none; color: #0b0080; text-decoration-line: none;"><span class="tocnumber" style="color: #222222; display: table-cell; padding-left: 0px; padding-right: 0.5em; text-decoration: inherit;">1</span><span class="toctext" style="display: table-cell; text-decoration: inherit;">Characteristics</span></a></li> <li class="toclevel-1 tocsection-2" style="margin-bottom: 0.1em;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#Historical" style="background: none; color: #0b0080; text-decoration-line: none;"><span class="tocnumber" style="color: #222222; display: table-cell; padding-left: 0px; padding-right: 0.5em; text-decoration: inherit;">2</span><span class="toctext" style="display: table-cell; text-decoration: inherit;">Historical</span></a></li> <li class="toclevel-1 tocsection-3" style="margin-bottom: 0.1em;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#References" style="background: none; color: #0b0080; text-decoration-line: none;"><span class="tocnumber" style="color: #222222; display: table-cell; padding-left: 0px; padding-right: 0.5em; text-decoration: inherit;">3</span><span class="toctext" style="display: table-cell; text-decoration: inherit;">References</span></a></li> <li class="toclevel-1 tocsection-4" style="margin-bottom: 0.1em;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#Bibliography" style="background: none; color: #0b0080; text-decoration-line: none;"><span class="tocnumber" style="color: #222222; display: table-cell; padding-left: 0px; padding-right: 0.5em; text-decoration: inherit;">4</span><span class="toctext" style="display: table-cell; text-decoration: inherit;">Bibliography</span></a></li> <li class="toclevel-1 tocsection-5" style="margin-bottom: 0.1em;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#External_links" style="background: none; color: #0b0080; text-decoration-line: none;"><span class="tocnumber" style="color: #222222; display: table-cell; padding-left: 0px; padding-right: 0.5em; text-decoration: inherit;">5</span><span class="toctext" style="display: table-cell; text-decoration: inherit;">External links</span></a></li> </ul> </div> <h2 style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; border-bottom: 1px solid rgb(162, 169, 177); color: black; font-family: "Linux Libertine", Georgia, Times, serif; font-weight: normal; line-height: 1.3; margin: 1em 0px 0.25em; overflow: hidden; padding: 0px;"> <span class="mw-headline" id="Characteristics">Characteristics</span><span class="mw-editsection" style="font-family: sans-serif; font-size: x-small; line-height: 1em; margin-left: 1em; vertical-align: baseline; white-space: nowrap;"><span class="mw-editsection-bracket" style="color: #54595d; margin-right: 0.25em;">[</span><a href="https://en.wikipedia.org/w/index.php?title=Asthenosphere&action=edit&section=1" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Edit section: Characteristics">edit</a><span class="mw-editsection-bracket" style="color: #54595d; margin-left: 0.25em;">]</span></span></h2> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> The asthenosphere is a part of the upper mantle just below the <a href="https://en.wikipedia.org/wiki/Lithosphere" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Lithosphere">lithosphere</a> that is involved in <a href="https://en.wikipedia.org/wiki/Plate_tectonics" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Plate tectonics">plate tectonic movement</a> and <a href="https://en.wikipedia.org/wiki/Isostasy" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Isostasy">isostatic</a> adjustments. The lithosphere-asthenosphere boundary is conventionally taken at the 1300 °C <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Isotherm_(contour_line)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Isotherm (contour line)">isotherm</a>, above which the mantle behaves in a rigid fashion and below which it behaves in a <a href="https://en.wikipedia.org/wiki/Ductility_(Earth_science)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Ductility (Earth science)">ductile</a> fashion.<sup class="reference" id="cite_ref-GeolSoc_6-0" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-GeolSoc-6" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[6]</a></sup> <a href="https://en.wikipedia.org/wiki/Seismic_wave" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Seismic wave">Seismic waves</a> pass relatively slowly through the asthenosphere<sup class="reference" id="cite_ref-7" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-7" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[7]</a></sup> compared to the overlying lithospheric mantle, thus it has been called the <i><a href="https://en.wikipedia.org/wiki/Low-velocity_zone" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Low-velocity zone">low-velocity zone</a></i> (LVZ), although the two are not exactly the same.<sup class="reference" id="cite_ref-8" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-8" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[8]</a></sup><sup class="reference" id="cite_ref-9" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-9" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[9]</a></sup> This decreasing in seismic waves velocity from lithosphere to asthenosphere could be caused by the presence of a very small percentage of melt in the asthenosphere. The lower boundary of the LVZ lies at a depth of 180–220 km,<sup class="reference" id="cite_ref-Condie_10-0" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-Condie-10" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[10]</a></sup> whereas the base of the asthenosphere lies at a depth of about 700 km.<sup class="reference" id="cite_ref-Kearey_11-0" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-Kearey-11" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[11]</a></sup> This was the observation that originally alerted <a href="https://en.wikipedia.org/wiki/Seismology" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Seismology">seismologists</a> to its presence and gave some information about its physical properties, as the speed of seismic waves decreases with decreasing <a href="https://en.wikipedia.org/wiki/Stiffness" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Stiffness">rigidity</a>.</div> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> In the old <a href="https://en.wikipedia.org/wiki/Ocean" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Ocean">oceanic</a> <a href="https://en.wikipedia.org/wiki/Mantle_(geology)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Mantle (geology)">mantle</a> the transition from the lithosphere to the asthenosphere, the lithosphere-asthenosphere boundary (LAB) is shallow (about 60 km in some regions) with a sharp and large velocity drop (5–10%).<sup class="reference" id="cite_ref-12" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-12" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[12]</a></sup> At the <a href="https://en.wikipedia.org/wiki/Mid-ocean_ridge" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Mid-ocean ridge">mid-ocean ridges</a> the LAB rises to within a few kilometers of the ocean floor.</div> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> The upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Tectonic_plate" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Tectonic plate">plates of the Earth's crust</a> move about. Due to the <a href="https://en.wikipedia.org/wiki/Temperature" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Temperature">temperature</a> and <a href="https://en.wikipedia.org/wiki/Pressure" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Pressure">pressure</a> conditions in the asthenosphere, <a href="https://en.wikipedia.org/wiki/Rock_(geology)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Rock (geology)">rock</a> becomes <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Ductile" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Ductile">ductile</a>, moving at rates of deformation measured in cm/yr over lineal distances eventually measuring thousands of kilometers. In this way, it flows like a <a href="https://en.wikipedia.org/wiki/Convection" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Convection">convection</a> 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 <a href="https://en.wikipedia.org/wiki/Fault_(geology)" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Fault (geology)">faults</a>. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere, allowing the movement of <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Tectonic_plates" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Tectonic plates">tectonic plates</a>.<sup class="reference" id="cite_ref-13" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-13" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[13]</a></sup><sup class="reference" id="cite_ref-14" style="font-size: 11.2px; line-height: 1; unicode-bidi: isolate; white-space: nowrap;"><a href="https://en.wikipedia.org/wiki/Asthenosphere#cite_note-14" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;">[14]</a></sup></div> <h2 style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; border-bottom: 1px solid rgb(162, 169, 177); color: black; font-family: "Linux Libertine", Georgia, Times, serif; font-weight: normal; line-height: 1.3; margin: 1em 0px 0.25em; overflow: hidden; padding: 0px;"> <span class="mw-headline" id="Historical">Historical</span><span class="mw-editsection" style="font-family: sans-serif; font-size: x-small; line-height: 1em; margin-left: 1em; vertical-align: baseline; white-space: nowrap;"><span class="mw-editsection-bracket" style="color: #54595d; margin-right: 0.25em;">[</span><a href="https://en.wikipedia.org/w/index.php?title=Asthenosphere&action=edit&section=2" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Edit section: Historical">edit</a><span class="mw-editsection-bracket" style="color: #54595d; margin-left: 0.25em;">]</span></span></h2> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> Although its presence was suspected as early as 1926, the worldwide occurrence of the asthenosphere was confirmed by analyses of seismic waves from the 9.5 <a href="https://en.wikipedia.org/wiki/Moment_magnitude_scale" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Moment magnitude scale">M<sub style="font-size: 11.2px; line-height: 1;">w</sub></a> <a class="mw-redirect" href="https://en.wikipedia.org/wiki/Great_Chilean_earthquake" style="background-attachment: initial; background-clip: initial; background-image: none; background-origin: initial; background-position: initial; background-repeat: initial; background-size: initial; color: #0b0080; text-decoration-line: none;" title="Great Chilean earthquake">Great Chilean earthquake</a> of May 22, 1960.</div> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> <br /></div> <div style="margin-bottom: 0.5em; margin-top: 0.5em;"> <br /></div> <div style="background-color: white; box-sizing: border-box; color: #1f1f1f; font-family: "open sans", "helvetica neue", arial, sans-serif; font-size: 19px; margin-bottom: 1.3em; margin-top: 10px;"> Both the lithosphere and asthenosphere are part of Earth and are made of similar material. Lithosphere is made up of Earth's outermost layer, the crust, and the uppermost portion of the mantle. In comparison, the asthenosphere is the upper portion of Earth's mantle (which is also the middle layer of Earth). The lithosphere lies over the asthenosphere. In fact, if any material from the asthenosphere were to solidify, it would become part of the lithosphere.</div> <div style="background-color: white; box-sizing: border-box; color: #1f1f1f; font-family: "open sans", "helvetica neue", arial, sans-serif; font-size: 19px; margin-bottom: 1.3em; margin-top: 1em;"> Being closer to the Earth's core, the asthenosphere is a higher temperature as compared to the lithosphere and hence its rocks are plastic and can flow. In comparison, the lithosphere's rocks are more rigid. The asthenosphere is more dense and viscous in comparison to the lithosphere. The lithosphere is comprised of a large number of fragments, each of which is known as the tectonic plate. These tectonic plates are in constant motion and are floating over the plastic material underneath.<br /> <br /> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 0px 0px 10px; vertical-align: baseline;"> <mathjax><span class="mjx-chtml MathJax_CHTML" id="MathJax-Element-1-Frame" style="border: 0px; direction: ltr; display: inline-block; float: none; font-family: inherit; font-size: 17.6px; font-stretch: inherit; font-variant: inherit; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; vertical-align: baseline; white-space: nowrap; word-spacing: normal;" tabindex="0"><span class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; border: 0px; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mrow" id="MJXc-Node-2" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mstyle" id="MJXc-Node-3" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mrow" id="MJXc-Node-4" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mstyle" id="MJXc-Node-5" style="border: 0px; box-sizing: content-box; color: darkorange; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mrow" id="MJXc-Node-6" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mrow" id="MJXc-Node-7" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-mtext" id="MJXc-Node-8" style="border: 0px; box-sizing: content-box !important; display: inline-block; font: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><span class="mjx-char MJXc-TeX-main-R" style="border: 0px; box-sizing: content-box; display: block; font-family: ,; font-size: inherit; font-stretch: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0.401em 0px 0.514em; vertical-align: baseline; white-space: pre;">The asthenosphere</span></span></span></span></span></span></span></span></span></span></mathjax> <span style="border: 0px; font-family: inherit; font-size: inherit; font-stretch: inherit; font-style: inherit; font-variant: inherit; font-weight: 700; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">is a layer (zone) of Earth’s mantle lying beneath the lithosphere.</span></div> <ul style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; list-style-image: initial; list-style-position: initial; margin: 0px; padding: 10px 0px 10px 25px; vertical-align: baseline;"> <li style="border: 0px; font: inherit; margin: 0px 0px 10px; padding: 0px; vertical-align: baseline;"><div style="border: 0px; font: inherit; margin-bottom: 10px; padding: 0px; vertical-align: baseline;"> It is a layer of solid rock that has so much pressure and heat the rocks can flow like a liquid.</div> </li> <li style="border: 0px; font: inherit; margin: 0px 0px 10px; padding: 0px; vertical-align: baseline;"><div style="border: 0px; font: inherit; margin-bottom: 10px; padding: 0px; vertical-align: baseline;"> The rocks are also less dense than the rocks in the lithosphere</div> </li> <li style="border: 0px; font: inherit; margin: 0px 0px 10px; padding: 0px; vertical-align: baseline;"><div style="border: 0px; font: inherit; margin-bottom: 10px; padding: 0px; vertical-align: baseline;"> It is believed to be much hotter and more fluid than the lithospher</div> </li> <li style="border: 0px; font: inherit; margin: 0px 0px 10px; padding: 0px; vertical-align: baseline;"><div style="border: 0px; font: inherit; margin-bottom: 10px; padding: 0px; vertical-align: baseline;"> Asthenosphere extends from about 100 km (60 miles) to about 700 km (450 miles) below Earth’s surface</div> </li> </ul> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <img alt="https://en.wikipedia.org/wiki/Lithosphere#/media/File:Earth-cutaway-schematic-english.svg" src="https://d2jmvrsizmvf4x.cloudfront.net/ulxhIpGeTiiJ9fJiJATB_2000px-Earth-cutaway-schematic-english.svg.png" style="border: 0px; font: inherit; margin: 0px; max-width: 100%; padding: 0px; vertical-align: baseline;" /></div> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <br /></div> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <span style="font-family: "source sans pro" , "helvetica" , "arial" , sans-serif; font-size: 17px;">The asthenosphere is the ductile part of the earth just below the lithosphere, including the upper </span><a href="https://earthquake.usgs.gov/learn/glossary/?term=mantle" style="box-sizing: border-box; color: #4c2c92; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 17px; overflow-wrap: break-word;">mantle</a><span style="font-family: "source sans pro" , "helvetica" , "arial" , sans-serif; font-size: 17px;">. The asthenosphere is about 180 km thick.</span></div> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <span style="font-family: "source sans pro" , "helvetica" , "arial" , sans-serif; font-size: 17px;"><br /></span></div> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <img alt="asthenosphere" src="https://earthquake.usgs.gov/learn/glossary/images/MOHO.JPG" /></div> <div style="border: 0px; color: #333333; font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-numeric: inherit; line-height: inherit; padding: 10px 0px 0px; vertical-align: baseline;"> <br /></div> <h1 class="page-title" style="box-sizing: border-box; clear: both; color: #2d88ac; font-family: Arial, Helvetica, "Helvetica Neue", sans-serif; font-size: 21px; line-height: 1.1; margin: 0px; padding: 5px 0px 8px;"> Asthenosphere</h1> <br /> <section class="main-section col-sm-12" id="mainaside" style="box-sizing: border-box; clear: both; color: #333333; float: left; font-family: Arial, Helvetica, "Helvetica Neue", sans-serif; font-size: 13px; min-height: 1px; padding: 0px; position: relative; width: 690px;"><div class="block" id="block-encyclopediasearchstaticpageblockforinnerpage" style="box-sizing: border-box;"> </div> <div class="article-detail left-gap block block-" style="box-sizing: border-box;"> <div style="box-sizing: border-box;"> <b style="box-sizing: border-box; color: #515050; font-family: Arial, Helvetica, sans-serif;">asthenosphere </b><span class="noindex" style="box-sizing: border-box;">ăsthēn´əsfēr [<a href="https://www.infoplease.com/key-pronunciation-symbols" style="background-color: transparent; box-sizing: border-box; color: #2d88ac; text-decoration-line: none;">key</a>]</span>, 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 <a href="https://www.infoplease.com/encyclopedia/earth/geology-oceanography/info/lithosphere" style="background-color: transparent; box-sizing: border-box; color: #2d88ac; text-decoration-line: none;">lithosphere </a>. 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 <a href="https://www.infoplease.com/encyclopedia/earth/geology-oceanography/info/plate-tectonics" style="background-color: transparent; box-sizing: border-box; color: #2d88ac; text-decoration-line: none;">plate tectonics </a>). 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 <a href="https://www.infoplease.com/encyclopedia/earth/geology-oceanography/info/seismology" style="background-color: transparent; box-sizing: border-box; color: #2d88ac; text-decoration-line: none;">seismology </a>). 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 <a href="https://www.infoplease.com/encyclopedia/earth/geology-oceanography/info/earth" style="background-color: transparent; box-sizing: border-box; color: #2d88ac; text-decoration-line: none;">earth </a>.</div> <div style="box-sizing: border-box;"> <br /></div> <div style="box-sizing: border-box;"> <div class="widget etymology-list" id="etymology-anchor" style="border: 0px; box-sizing: border-box; color: #212529; font-family: Lato, Helvetica, Arial, sans-serif; font-size: 16px; font-stretch: inherit; font-variant-east-asian: inherit; font-variant-ligatures: no-common-ligatures; font-variant-numeric: inherit; letter-spacing: 0.2px; line-height: inherit; margin: 0px 0px 60px; padding: 0px; vertical-align: baseline;"> <h2 style="border: 0px; box-sizing: border-box; color: #265667; display: inline-block; font-family: "Open Sans", Helvetica, Arial, sans-serif; font-size: 22px; font-stretch: normal; font-variant: inherit; letter-spacing: 0.3px; line-height: 26px; margin: 0px 0px 0.5em; padding: 0px; vertical-align: baseline;"> History and Etymology for <em style="border: 0px; box-sizing: border-box; display: inline; font-family: inherit; font-size: inherit; font-stretch: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">asthenosphere</em></h2> <div class="et" style="border: 0px; box-sizing: border-box; color: #303336; font-family: "Open Sans", Helvetica, Arial, sans-serif; font-size: 18px; font-stretch: normal; font-style: inherit; font-variant: inherit; letter-spacing: 0.2px; line-height: 22px; margin-bottom: 20px; padding: 0px; vertical-align: baseline;"> Greek <em class="mw_t_it" style="border: 0px; box-sizing: border-box; font-family: inherit; font-size: inherit; font-stretch: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">asthenḗs</em> "weak" + <a class="mw_t_et_link" href="https://www.merriam-webster.com/dictionary/-o-#etymology" style="-webkit-tap-highlight-color: rgba(0, 0, 0, 0); background-color: transparent; background-image: linear-gradient(to right, rgb(151, 190, 206) 100%, transparent 0px); background-position: 0px 1.15em; background-repeat: repeat-x; background-size: 3px 1px; border: 0px; box-sizing: border-box; color: #265667; font: inherit; margin: 0px; outline: 0px; padding: 0px; text-decoration-line: none; text-transform: uppercase; vertical-align: baseline;">-O-</a> + <a class="mw_t_et_link" href="https://www.merriam-webster.com/dictionary/-sphere#etymology" style="-webkit-tap-highlight-color: rgba(0, 0, 0, 0); background-color: transparent; background-image: linear-gradient(to right, rgb(151, 190, 206) 100%, transparent 0px); background-position: 0px 1.15em; background-repeat: repeat-x; background-size: 3px 1px; border: 0px; box-sizing: border-box; color: #265667; font: inherit; margin: 0px; outline: 0px; padding: 0px; text-decoration-line: none; text-transform: uppercase; vertical-align: baseline;">-SPHERE</a> — more at <a class="mw_t_mat" href="https://www.merriam-webster.com/dictionary/asthenia#etymology" style="-webkit-tap-highlight-color: rgba(0, 0, 0, 0); background-color: transparent; background-image: linear-gradient(to right, rgb(151, 190, 206) 100%, transparent 0px); background-position: 0px 1.15em; background-repeat: repeat-x; background-size: 3px 1px; border: 0px; box-sizing: border-box; color: #265667; font: inherit; margin: 0px; outline: 0px; padding: 0px; text-decoration-line: none; text-transform: uppercase; vertical-align: baseline;">ASTHENIA</a></div> <div class="et_snote" style="border: 0px; box-sizing: border-box; color: #525a5b; font-family: "Open Sans", Helvetica, Arial, sans-serif; font-size: 18px; font-stretch: normal; font-variant: inherit; letter-spacing: 0.2px; line-height: 22px; padding: 0px; vertical-align: baseline;"> <span class="note-txt" style="border: 0px; box-sizing: border-box; font: inherit; margin: 0px; padding: 0px; text-transform: uppercase; vertical-align: baseline;">NOTE:</span> Term introduced by the American geologist Joseph Barrell (1869-1919) in "The strength of the earth's crust. Part VI. Relations of isostatic movements to a sphere of weakness—the asthenosphere," <em class="mw_t_it" style="border: 0px; box-sizing: border-box; font-family: inherit; font-size: inherit; font-stretch: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">Journal of Geology,</em> vol. 22 (1914), p. 659: "The theory of isostasy shows that below the lithosphere there exists in contradistinction a thick earth-shell marked by a capacity to yield readily to long-enduring strains of limited magnitude…To give proper emphasis and avoid the repetition of descriptive clauses it needs a distinctive name. It may be the generating zone of the pyrosphere; it may be a sphere of unstable state, but this to a large extent is hypothesis and the reason for choosing a name rests upon the definite part it seems to play in crustal dynamics. Its comparative weakness is in that connection its distinctive feature. It may then be called the sphere of weakness—<em class="mw_t_it" style="border: 0px; box-sizing: border-box; font-family: inherit; font-size: inherit; font-stretch: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">the asthenosphere</em>…"</div> <div> <br /></div> <div> <br /> <section style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"><h1 style="box-sizing: border-box; color: inherit; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 4.4rem; letter-spacing: -1pt; line-height: 1.1; margin: 20px 0px 10px;"> Asthenosphere</h1> <h2 style="box-sizing: border-box; color: inherit; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 2.8rem; line-height: 1.1; margin-bottom: 10px; margin-top: 20px;"> The Asthenosphere In Plate Tectonic Theory</h2> </section><br /> <div style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <ins class="adsbygoogle" data-ad-client="ca-pub-4803409109489353" data-ad-format="fluid" data-ad-layout="in-article" data-ad-slot="1410035154" data-adsbygoogle-status="done" style="box-sizing: border-box; display: block; height: 0px; text-align: center;"><ins id="aswift_0_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 749px;"><ins id="aswift_0_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 749px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="188" hspace="0" id="aswift_0" marginheight="0" marginwidth="0" name="aswift_0" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 188px; left: 0px; position: absolute; top: 0px; width: 749px;" vspace="0" width="749"></iframe></ins></ins></ins></div> <div class="netind_article" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> The asthenosphere is now thought to play a critical role in the movement of plates across the face of Earth's surface. According to plate tectonic theory, the lithosphere consists of a relatively small number of very large slabs of rocky material. These plates tend to be about 60 mi (100 km) thick and in most instances many thousands of miles wide. They are thought to be very rigid themselves but capable of being moved on top of the asthenosphere. The collision of plates with each other, their lateral sliding past each other, and their separation from each other are thought to be responsible for major geologic features and events such as volcanoes, lava flows, mountain building, and deep crustal faults and rifts.</div> <div style="box-sizing: border-box;"> <ins class="adsbygoogle" data-ad-client="ca-pub-4803409109489353" data-ad-format="fluid" data-ad-layout="in-article" data-ad-slot="1410035154" data-adsbygoogle-status="done" style="box-sizing: border-box; display: block; height: 0px; text-align: center;"><ins id="aswift_1_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 749px;"><ins id="aswift_1_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 749px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="188" hspace="0" id="aswift_1" marginheight="0" marginwidth="0" name="aswift_1" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 188px; left: 0px; position: absolute; top: 0px; width: 749px;" vspace="0" width="749"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> In order for plate tectonic theory to make any sense, some mechanism must be available for permitting the flow of plates. That mechanism is the semi-fluid character of the asthenosphere itself. Some observers have described the asthenosphere as the 'lubricating oil' that permits the movement of plates in the lithosphere. Others view the asthenosphere as the driving force or means of conveyance for the plates.</div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Geologists have now developed theories to explain the changes that take place in the asthenosphere when plates begin to diverge from or converge toward each other. For example, suppose that a region of weakness has developed in the lithosphere. In that case, the pressure exerted on the asthenosphere beneath it is reduced, melting begins to occur, and asthenospheric materials begin to flow upward. If the lithosphere has not actually broken, those asthenospheric materials cool as they approach Earth's surface and eventually become part of the lithosphere itself. On the other hand, suppose that a break in the lithosphere has actually occurred. In that case, the asthenospheric materials may escape through that break and flow outward before they have cooled. Depending on the temperature and pressure in the region, that outflow of material (<span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/4063/Magma.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">magma</a></span>) may occur rather violently, as in a <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/7257/Volcano.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">volcano</a></span>, or more moderately, as in a lave flow. Both these cases produce crustal plate divergence, or spreading apart. Pressure on the asthenosphere may also be reduced in zones of divergence, where two plates are separating from each other. Again, this reduction in pressure may allow asthenospheric materials in the asthenosphere to begin melting and to flow upward. If the two overlying plates have actually separated, asthenospheric material may flow through the separation and form a new section of lithosphere.</div> <div class="google-auto-placed ap_container" style="box-sizing: border-box; clear: none; height: auto; text-align: center; width: 748.813px;"> <ins class="adsbygoogle adsbygoogle-noablate" data-ad-client="ca-pub-4803409109489353" data-ad-format="auto" data-adsbygoogle-status="done" style="background-color: transparent; box-sizing: border-box; display: block; margin: auto;"><ins id="aswift_3_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 748px;"><ins id="aswift_3_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 748px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="187" hspace="0" id="aswift_3" marginheight="0" marginwidth="0" name="aswift_3" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 187px; left: 0px; position: absolute; top: 0px; width: 748px;" vspace="0" width="748"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> In zones of convergence, where two plates are moving toward each other, asthenospheric materials may also be exposed to increased pressure and begin to flow downward. In this case, the lighter of the colliding plates slides upward and over the heavier of the plates, which dives down into the asthenosphere. Since the heavier lithospheric material is more rigid than the material in the asthenosphere, the latter is pushed outward and upward. During this movement of plates, material of the downgoing plate is heated in the asthenosphere, melting occurs, and molten materials flow upward to Earth's surface. Mountain building is the result of continental collision in such situations, and great mountain chains like the Urals, Appalachian, and Himalayas have been formed in such a fashion. When oceanic plates meet one another, <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/3705/Island.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">island</a></span> arcs (e.g., Japan or the Aleutians) are formed. Great <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/4828/Ocean.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">ocean</a></span> trenches occur in places of plate convergence. In any one of the examples cited here, the asthenosphere supplies new material to replace lithospheric materials that have been displaced by some other tectonic or geologic mechanism.</div> <div class="google-auto-placed ap_container" style="box-sizing: border-box; clear: none; height: auto; text-align: center; width: 748.813px;"> <ins class="adsbygoogle adsbygoogle-noablate" data-ad-client="ca-pub-4803409109489353" data-ad-format="auto" data-adsbygoogle-status="done" style="background-color: transparent; box-sizing: border-box; display: block; margin: auto;"><ins id="aswift_4_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 748px;"><ins id="aswift_4_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 748px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="187" hspace="0" id="aswift_4" marginheight="0" marginwidth="0" name="aswift_4" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 187px; left: 0px; position: absolute; top: 0px; width: 748px;" vspace="0" width="748"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Therefore, whether scientists are considering the origin of compressed mountain ranges like the Himalayas, or the origin of the great ocean trenches (like the Peru-Chile trench), they also consider the activity of the asthenosphere, which keeps Earth's plates continually geologically active.</div> </div> <div class="netind_other" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> See also <a href="https://science.jrank.org/pages/1752/Continental-Drift.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">Continental drift</a>; <a href="https://science.jrank.org/pages/1757/Continental-Margin.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">Continental margin</a>; <a href="https://science.jrank.org/pages/1758/Continental-Shelf.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">Continental shelf</a>; <a href="https://science.jrank.org/pages/5259/Planetary-Geology.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">Planetary geology</a>; <a href="https://science.jrank.org/pages/5338/Plate-Tectonics.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">Plate tectonics</a>.</div> </div> <div class="netind_reference" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <h2 style="box-sizing: border-box; color: inherit; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 2.8rem; line-height: 1.1; margin-bottom: 10px; margin-top: 20px;"> Resources</h2> </div> <div class="netind_reference" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <h3 style="box-sizing: border-box; color: inherit; font-family: inherit; font-size: 2.6rem; font-weight: 500; line-height: 1.1; margin-bottom: 10px; margin-top: 20px;"> <small style="box-sizing: border-box; color: #777777; font-size: 16.9px; line-height: 1;">Books</small></h3> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Press, Frank, and Raymond Sevier. <i style="box-sizing: border-box;">Understanding Earth.</i> San Francisco: Freeman, 2000.</div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Tarbuck, Edward. J., Frederick K. Lutgens, and Dennis Tassa, eds. <i style="box-sizing: border-box;">Earth: An Introduction to Physical Geology,</i> 7th ed. Upper Saddle River, NJ: Prentice Hall, 2002.</div> <div class="google-auto-placed ap_container" style="box-sizing: border-box; clear: none; height: auto; text-align: center; width: 748.813px;"> <ins class="adsbygoogle adsbygoogle-noablate" data-ad-client="ca-pub-4803409109489353" data-ad-format="auto" data-adsbygoogle-status="done" style="background-color: transparent; box-sizing: border-box; display: block; margin: auto;"><ins id="aswift_5_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 748px;"><ins id="aswift_5_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 748px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="187" hspace="0" id="aswift_5" marginheight="0" marginwidth="0" name="aswift_5" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 187px; left: 0px; position: absolute; top: 0px; width: 748px;" vspace="0" width="748"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Fuchs, Karl, and Claude Froidevaux. <i style="box-sizing: border-box;">Composition, Structure, and Dynamics of the Lithosphere and Asthenosphere System.</i> Washington, DC: American Geophysical Union, 1987.</div> </div> <div class="netind_other" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> David E. Newton</div> </div> <div class="netind_sidebar" style="box-sizing: border-box; color: #333337; font-family: "Droid Serif", serif; font-size: 6.25px; font-variant-ligatures: normal; letter-spacing: normal;"> <h2 style="box-sizing: border-box; color: inherit; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 2.8rem; line-height: 1.1; margin-bottom: 10px; margin-top: 20px;"> KEY TERMS</h2> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> <small style="box-sizing: border-box; font-size: 17.85px;"><span style="box-sizing: border-box; font-weight: 700;">. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</span></small></div> <dl style="box-sizing: border-box; margin-bottom: 20px; margin-top: 0px;"> <dt style="box-sizing: border-box; font-weight: 700; line-height: 1.42857;"><span style="box-sizing: border-box;">Lithosphere</span></dt> <dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> —The outer layer of Earth, that extends to a depth of about 60 mi (100 km).</div> </dd> <dt style="box-sizing: border-box; font-weight: 700; line-height: 1.42857;"><span style="box-sizing: border-box;">Magma</span></dt> <dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> —Molten material exuded from below Earth's surface, generally consisting of rock-like materials rich in silicon and oxygen.</div> </dd> <dt style="box-sizing: border-box; font-weight: 700; line-height: 1.42857;"><span style="box-sizing: border-box;">Seismic wave</span></dt> <dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> —A disturbance produced by compression or distortion on or within the earth, which propagates through Earth materials; a seismic wave may be produced by natural (e.g. earthquakes) or artificial (e.g. explosions) means.</div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> The material of which the asthenosphere is composed can be described as plastic-like, with much less rigidity than the lithosphere above it. This property is caused by the interaction of <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/6748/Temperature.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">temperature</a></span> and <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/5479/Pressure.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">pressure</a></span> on asthenospheric materials. Any rock will, of course, melt if its temperature is raised to a high enough temperature. However, the melting point of any rock (or of any material) is also a function of the pressure exerted on the rock (or the material). In general, as the pressure is increased on a material, its melting point increases.</div> <div style="box-sizing: border-box;"> <ins class="adsbygoogle" data-ad-client="ca-pub-4803409109489353" data-ad-format="fluid" data-ad-layout="in-article" data-ad-slot="1410035154" data-adsbygoogle-status="done" style="box-sizing: border-box; display: block; height: 0px; text-align: center;"><ins id="aswift_1_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 749px;"><ins id="aswift_1_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 749px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="188" hspace="0" id="aswift_1" marginheight="0" marginwidth="0" name="aswift_1" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 188px; left: 0px; position: absolute; top: 0px; width: 749px;" vspace="0" width="749"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Materials that make up the asthenosphere tend to be slightly cooler than their melting point. This gives them a plastic-like quality that can be compared to <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/3056/Glass.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">glass</a></span>. As the temperature of the material increases or as the pressure exerted on the material increases, the material tends to deform and flow. If the pressure on the material is sharply reduced, so will be its melting point, and the material may begin to melt quickly. The fragile melting point/pressure balance in the asthenosphere is reflected in the estimate made by some geologists that up to 10% of the asthenospheric material may actually be molten. The rest is so close to being molten that relatively modest changes in pressure or temperature may cause further melting.</div> <div class="google-auto-placed ap_container" style="box-sizing: border-box; clear: none; height: auto; text-align: center; width: 748.813px;"> <ins class="adsbygoogle adsbygoogle-noablate" data-ad-client="ca-pub-4803409109489353" data-ad-format="auto" data-adsbygoogle-status="done" style="background-color: transparent; box-sizing: border-box; display: block; margin: auto;"><ins id="aswift_3_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 748px;"><ins id="aswift_3_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 748px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="187" hspace="0" id="aswift_3" marginheight="0" marginwidth="0" name="aswift_3" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 187px; left: 0px; position: absolute; top: 0px; width: 748px;" vspace="0" width="748"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> In addition to loss of pressure on the asthenosphere, another factor that can bring about melting is an increase in temperature. The asthenosphere is heated by contact with hot materials that make up the mesosphere beneath it. Obviously, the temperature of the mesosphere is not constant. It is hotter in some places than in others. In those regions where the mesosphere is warmer than average, the extra <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/3262/Heat.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">heat</a></span> may actually increase the extent to which asthenospheric materials are heated and a more extensive melting may occur. The results of such an event are described below.</div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><br /> <section style="box-sizing: border-box;"><h2 style="box-sizing: border-box; color: inherit; font-family: "Source Sans Pro", Helvetica, Arial, sans-serif; font-size: 2.8rem; line-height: 1.1; margin-bottom: 10px; margin-top: 20px;"> Evidence For The Existence Of The Asthenosphere</h2> </section><br /> <div style="box-sizing: border-box;"> <ins class="adsbygoogle" data-ad-client="ca-pub-4803409109489353" data-ad-format="fluid" data-ad-layout="in-article" data-ad-slot="1410035154" data-adsbygoogle-status="done" style="box-sizing: border-box; display: block; height: 0px; text-align: center;"><ins id="aswift_0_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 749px;"><ins id="aswift_0_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 749px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="188" hspace="0" id="aswift_0" marginheight="0" marginwidth="0" name="aswift_0" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 188px; left: 0px; position: absolute; top: 0px; width: 749px;" vspace="0" width="749"></iframe></ins></ins></ins></div> <div class="netind_article" style="box-sizing: border-box;"> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> Geologists are somewhat limited as to the methods by which they can collect information about <span style="box-sizing: border-box; font-weight: 700;">Earth's interior</span>. For example, they may be able to study rocky material ejected from volcanoes and lava flows for hints about properties of the interior regions. Generally speaking, however, the single most dependable source of such information is the way in which seismic waves are transmitted through Earth's interior. These waves can be produced naturally as the result of earth movements, or they can be generated synthetically by means of explosions, air guns, or other techniques.</div> <div style="box-sizing: border-box;"> <ins class="adsbygoogle" data-ad-client="ca-pub-4803409109489353" data-ad-format="fluid" data-ad-layout="in-article" data-ad-slot="1410035154" data-adsbygoogle-status="done" style="box-sizing: border-box; display: block; height: 0px; text-align: center;"><ins id="aswift_1_expand" style="background-color: transparent; border: none; box-sizing: border-box; display: inline-table; height: 0px; margin: 0px; padding: 0px; position: relative; visibility: visible; width: 749px;"><ins id="aswift_1_anchor" style="background-color: transparent; border: none; box-sizing: border-box; display: block; height: 0px; margin: 0px; opacity: 0; overflow: hidden; padding: 0px; position: relative; visibility: visible; width: 749px;"><iframe allowfullscreen="true" allowtransparency="true" frameborder="0" height="188" hspace="0" id="aswift_1" marginheight="0" marginwidth="0" name="aswift_1" scrolling="no" style="border-style: initial; border-width: 0px; box-sizing: border-box; height: 188px; left: 0px; position: absolute; top: 0px; width: 749px;" vspace="0" width="749"></iframe></ins></ins></ins></div> <div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> In any case, seismic studies have shown that a type of waves known as S-waves slow down significantly as they reach an average depth of about 62 mi (100 km) beneath Earth's surface. Then, at a depth of about 155 mi (250 km), their <span style="box-sizing: border-box; font-weight: 700;"><a href="https://science.jrank.org/pages/7161/Velocity.html" style="background: 0px 0px; border-bottom: 1px solid rgb(250, 250, 250); box-sizing: border-box; color: #999999; text-decoration-line: none;">velocity</a></span> increases once more. Geologists have taken these changes in wave velocity as indications of the boundaries for the region now known as the asthenosphere.</div> </div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="box-sizing: border-box; font-size: 2.1rem; margin-bottom: 30px;"> <br /></div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><h1 style="color: #2e3192; font-family: Arial, Helvetica, sans-serif; font-size: 1.4em; font-style: italic; margin-bottom: 5px; margin-left: 12px; margin-top: 0px;"> The Earth's Crust, Lithosphere and Asthenosphere<iframe allowtransparency="true" frameborder="0" scrolling="no" src="https://www.facebook.com/plugins/like.php?href=http%3A%2F%2Fwww.windows2universe.org/earth/interior/earths_crust.html&send=false&layout=button_count&width=100&show_faces=false&action=like&colorscheme=light&font&height=21&appId=325911867506691" style="border-style: none; border-width: initial; float: right; height: 21px; overflow: hidden; width: 100px;"></iframe></h1> <div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> <b>Crust</b>, the upper <a href="https://www.windows2universe.org/earth/Interior_Structure/interior.html" style="outline: none;">layer</a> of the Earth, is not always the same. Crust under the oceans is only about 5 km thick while continental crust can be up to 65 km thick. Also, ocean crust is made of denser minerals than continental crust.</div> <div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> The tectonic plates are made up of Earth’s crust and the upper part of the mantle layer underneath. Together the crust and upper mantle are called the <b>lithosphere</b> and they extend about 80 km deep. The lithosphere is broken into giant plates that fit around the globe like puzzle pieces. These puzzle pieces <a href="https://www.windows2universe.org/earth/interior/plate_tectonics.html" style="outline: none;">move</a> a little bit each year as they slide on top of a somewhat fluid part of the mantle called the asthenosphere. All this moving rock can cause <a href="https://www.windows2universe.org/earth/geology/quake_1.html" style="outline: none;">earthquakes</a>.</div> <div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> The <b>asthenosphere</b> is ductile and can be pushed and deformed like silly putty in response to the warmth of the Earth. These rocks actually flow, moving in response to the stresses placed upon them by the churning motions of the deep interior of the Earth. The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back.</div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> <br /></div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> Flow in the asthenosphere drags tectonic plates along by Rice University A 3D computer model of the asthenosphere by Rice University geophysicists finds that the convective cycling and pressuredriven flow can sometimes cause the asthenosphere to move even faster than the tectonic plates riding atop it. This 2D slice of data from the model shows stronger, faster moving sections of the asthenosphere (yellow) bracketed above and below by slower, more fluid regions (orange). Credit: A. Semple/Rice University New simulations of Earth's asthenosphere find that convective cycling and pressure-driven flow can sometimes cause the planet's most fluid layer of mantle to move even faster than the tectonic plates that ride atop it. That's one conclusion from a new study by Rice University geophysicists who modeled flow in the 100- mile-thick layer of mantle that begins at the base of Earth's tectonic plates, or lithosphere. The study, which is available online in the journal Earth and Planetary Science Letters, takes aim at a much-debated question in geophysics: What drives the movement of Earth's tectonic plates, the 57</div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> <br /></div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> interlocking slabs of the lithosphere that slip, grind and bump against one another in a seismic dance that causes earthquakes, builds continents and gradually reshapes the planet's surface every few million years? "Tectonic plates float on top of the asthenosphere, and the leading theory for the past 40 years is that the lithosphere moves independently of the asthenosphere, and the asthenosphere only moves because the plates are dragging it along," said graduate student Alana Semple, lead co-author of the new study. "Detailed observations of the asthenosphere from a Lamont research group returned a more nuanced picture and suggested, among other things, that the asthenosphere has a constant speed at its center but is changing speeds at its top and base, and that it sometimes appears to flow in a different direction than the lithosphere." Computational modeling carried out at Rice offers a theoretical framework that can explain these puzzling observations, said Adrian Lenardic, a study co-author and professor of Earth, environmental and planetary sciences at Rice. "We've shown how these situations can occur through a combination of plate- and pressure-driven flow in the asthenosphere," he said. "The key was realizing that a theory developed by former Rice postdoc Tobias Höink had the potential to explain the Lamont observations if a more accurate representation of the asthenosphere's viscosity was allowed for. Alana's numerical simulations incorporated that type of viscosity and showed that the modified model could explain the new observations. In the process, this offered a new way of thinking about the relationship between the lithosphere and asthenosphere." Though the asthenosphere is made of rock, it is under intense pressure that can cause its contents to flow. "Thermal convection in Earth's mantle generates dynamic pressure variations," Semple said. "The weakness of the asthenosphere, relative to tectonic plates above, allows it to respond differently to the pressure variations. Our models show how this can lead to asthenosphere velocities that exceed those of plates above. The models also show how flow in the asthenosphere can be offset from that of plates, in line with the observations from the Lamont group" The oceanic lithosphere is formed at mid-ocean ridges and flows toward subduction zones where one tectonic plate slides beneath another. In the process, the lithosphere cools and heat from Earth's interior is transferred to its surface. Subduction recycles cooler lithospheric material into the mantle, and the cooling currents flow back into the deep interior. Semple's 3-D model simulates both this convective cycle and the asthenosphere. She credited Rice's Center for Research Computing (CRC) for its help running simulations—some of which took as long as six weeks—on Rice's DAVinCI supercomputer. Semple said the simulations show how convective cycling and pressure-driven flow can drive tectonic movement. "Our paper suggests that pressure-driven flow in the asthenosphere can contribute to the motion of tectonic plates by dragging plates along with it," she said. "A notable contribution does come from 'slab-</div> </dd><dd style="box-sizing: border-box; line-height: 1.42857; margin-left: 0px;"><div style="color: black; font-family: Arial, Helvetica, sans-serif; font-size: 12.8px;"> pull,' a gravity-driven process that pulls plates toward subduction zones. Slab-pull can still be the dominant process that moves plates, but our models show that asthenosphere flow provides a more significant contribution to plate movement than previously thought." </div> </dd></dl> </div> </div> </div> </div> </div> </section></div> </div> </div> </div> </div>

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Asthenosphere From Wikipedia, the free encyclopedia Jump to navigation Jump to search The asthenosphere shown at a  su...

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