Notes Part 2

Notes Part 2 - GEOL 240Lxg Notes 10-8-09 1.1 Samoa...

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GEOL 240Lxg Notes 10-8-09 Samoa Earthquake –subduction zone, magnitude 8.0, tension, normal fault, big tsunami , 10 km deep 1.1 Body waves o P waves (compressional waves): Travel at speeds of 6-8 km/s through the earth’s interior. Particle motion is parallel to direction of propagation. Also called primary waves (thus the P). similar to sound waves. o S waves (shear waves) Travel at speeds of 3-5 km/s through the earth’s interior. Particle motion is perpendicular to direction of propagation. Also called secondary waves (thus the S). Do not pass through liquids. Surface waves – Travel at speeds less than 3-4 km/s. They consist of dispersed wave trains (different frequencies travel at different velocities) that travel around the earth at its surface. o Rayleigh waves Particle motion is horizontal and perpendicular to the direction of propagation.
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o Love waves Particle motion is retrograde elliptical in direction of propagation. Snell’s Law Mode conversion 1.3 SV/SH Mode conversion 1.4 P/SV No mode conversion 1.5 SH Total Internal Reflection 1.6 o Example with light Fish tank
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o Example with air On a road o Example with water In a pool
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Earth with increasing P-wave and s-wave Structure of the Crust and Upper Mantle Only known the structure of the earth since the 1920’s Earth has a layered structure (onion) base on composition 3 main layers o Crust Moho o Mantle o Core Crust o Continental Crust Lower density, quartz SiO2, feldspars, basalt, variable thickness (20-50 km) o Oceanic crust Higher density, basalt, constant thickness (uniform in thickness about 10km)
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The crust (isostacy) floats on the denser mantle (ultra mafic minerals – Olivine ( Mg , Fe ) 2 Si O 4 , Pylaxene (Mg,Fe)SiO 3 ) below GEOL 240Lxg Notes 10-13-09 Earthquakes make seismic waves o Body waves P waves Mode conversion SV S waves SV o Mode conversion P SH o Do not mode convert o Surface waves Rayleigh waves Always have on any surface Love waves SH waves trapped in the crust by total internal reflection Require a low velocity surface layer
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Earth has a low velocity crust 2.1 Crust Lowest density of all the layers Low density silicates Floats on denser mantle “isostacy” o Continental Lowest density Variable thickness Deeper under mountains Shallower under low lying planes White rocks – quartz, feldspar o Oceanic Higher density Not much quartz or feldspar Dark/black rocks – basalt, mostly ultramafic minerals, olivine Basalt comes out of the mantle lowest part of mantle coming up Uniform thickness about 10km 2.2 Mantle 2.3 Upper mantle o Moho 650km Carbon
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o Graphite o Coal o Diamond Temperature in Earth 2.4 Core o Mostly iron, nickel (10%), sulfur (5%)
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This note was uploaded on 11/08/2009 for the course GEOL 240Lxg taught by Professor 12:30-01:50pm during the Fall '07 term at USC.

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Notes Part 2 - GEOL 240Lxg Notes 10-8-09 1.1 Samoa...

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