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rheological (or mechanical) layering rheological layers lithosphere: rigid & strong asthenosphere: plastic & weak mesosphere: plastic but stronger chemical layers crust: low density silicate mantle: medium density silicate core: iron-nickel metal lithosphere: temperature well below the melting temperature LVZ: partial melting asthenosphere: temperature near melting temperature mesosphere: temperature well below melting T STRONG WEAK GETTING STRONGER Brittle deformation of the lithosphere occurs by fault motion. Fault motion produces earthquakes Modern seismicity (earthquakes) records fault motion along plate margins. Seismicity is confined to the brittle lithosphere. Deep earthquakes occur in subducted lithosphere (Benioff -Waditi zone) At high temperature (near the melting T) rocks are weak can flow Ductile flow occurs in the solid state lithosphere is rigid, asthenosphere flows lithosphere: cold mantle LVZ: partial melting asthenosphere: hot mantle heating lithosphere makes asthenosphere cooling asthenosphere makes lithosphere sinking lithosphere at a subduction zone becomes asthenosphere rising asthenosphere at a MOR becomes lithosphere
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