unit seven.ppt - Earths Interior and Geophysical Properties...

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Earth’s Interior and Earth’s Interior and Geophysical Properties Geophysical Properties
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Introduction Introduction Deep interior of the Earth must be studied indirectly direct access only to crustal rocks and small upper mantle fragments brought up by volcanic eruptions or slapped onto continents by subducting oceanic plates deepest drillhole reached about 12 km, but did not reach the mantle Geophysics the branch of geology that studies the interior of the Earth Insert CO 17
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Evidence from Seismic Evidence from Seismic Waves Waves Seismic waves – vibrations from a large earthquake will pass through the entire Earth Seismic reflection – the return of some waves to the surface after bouncing off a rock layer boundary sharp boundary between two materials of different densities will reflect seismic waves Seismic refraction bending of seismic waves as they pass from one material to another having different seismic wave velocities
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Earth’s Internal Earth’s Internal Structure Structure Main zones within the Earth: C rust – the outer layer of rock that forms a thin skin on Earth’s surface Mantle – a thick shell of dense rock that separates the crust above from the core below Core the metallic central zone of the Earth
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The The Crust Crust Seismic waves – indicate crust is thinner and denser beneath the oceans than on the continents different seismic wave velocities are indicative of different compositions oceanic crust is mafic , composed primarily of basalt and gabbro continental crust is felsic , with an average composition similar to granite
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The Mantle The Mantle The mantle, like the crust, is made of solid rock with only isolated pockets of magma higher seismic wave velocities of mantle vs. crustal rocks indicative of denser, ultramafic composition crust and upper mantle together form the lithosphere , the brittle outer shell of the Earth that makes up the tectonic plates Beneath the lithosphere, seismic wave speeds abruptly decrease in a plastic low-velocity zone called the asthenosphere
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The Core The Core Primary evidence for existence and nature of Earth’s core specific areas on the opposite side of the Earth from large earthquakes do not receive seismic waves, resulting in seismic shadow zones P-wave shadow zone (103°-142° from epicenter) explained by refraction of waves encountering core-mantle boundary S-wave shadow zone (≥103° from epicenter) suggests outer core is a liquid careful observations of P-wave refraction patterns indicate inner core is solid
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The The Core Core
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  • Spring '14
  • AnatoleDolgoff

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