chapter_17_powerpt.CM-11e

chapter_17_powerpt.CM-11e - Earths Interior and Geophysical...

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Steve Kadel, Glendale Community College Earth’s Interior and Geophysical Properties Physical Geology 11/e, Chapter 17
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Introduction Deep parts of Earth must be studied indirectly Direct access is only available to crustal rocks and small upper mantle fragments brought up by volcanic eruptions or slapped onto continents from subducting oceanic plates Deepest hole ever drilled is 12 km deep and did not reach the mantle Geophysics is the branch of geology that studies the interior of the Earth includes the study of seismic waves and Earth’s magnetic field, gravity, and heat Box 17.1, Fig. 1
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Seismic Energy (From Tarbuck & Lutgens, 8e)
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Evidence from Seismic Waves Seismic waves or vibrations from a large earthquake (or nuclear bomb blast) will pass through the entire Earth Seismic reflection is the return of some waves to the surface after bouncing off a rock boundary Two materials of different densities separated by a sharp boundary will lead to reflection of seismic waves off the boundary Depth to the boundary can be calculated by measuring time Seismic refraction is the bending of seismic waves as they pass from one material to another with different seismic wave velocities
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Fig. 17.1 Seismic reflection
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Fig. 17.2 Fig. 17.2 Seismic refraction occurs when seismic waves bend as they cross rock boundaries
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Fig. 17.3 Seismic refraction can be used to detect boundaries between rock layers
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Earth’s Internal Structure Seismic waves have been used to determine the three main zones (based on composition) within the Earth: the crust , mantle and core The crust is the outer layer of rock that forms a thin skin on Earth’s surface The mantle is a thick shell of dense rock that separates the crust above from the core below The core is the metallic central zone of the Earth
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Fig. 17.5 Fig. 17.5 Earth’s interior
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The Crust Seismic wave studies have indicated that the crust is thinner and denser beneath the oceans than on the continents Different seismic wave velocities in oceanic (7 km/sec) vs. continental (~6 km/sec) crustal rocks 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 Crust The Moho (Mohorovicic discontinuity) Discovered in 1909 by Andriaja Mohorovicic Separates crustal materials from underlying mantle Identified by a change in the velocity of P-waves (From Tarbuck & Lutgens, 8e)
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This note was uploaded on 06/13/2011 for the course GEOL 1403 taught by Professor Mulcahey during the Spring '11 term at Lone Star College System.

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chapter_17_powerpt.CM-11e - Earths Interior and Geophysical...

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