Lecture 4 - Earth Structure

Lecture 4 - Earth Structure - Lecture 4 Earth Structure...

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Lecture 4 Earth Structure
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Earth consists of a  series of concentric  layers or spheres  which differ in  chemistry  and  physical   properties. Chemical Layers Physical Layers
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How Do We Really Know What Earth’s Interior Looks Like? Meteorites Seismic Studies
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Bore Holes - max 13Km bore holes are drilled to investigate the subsurface geology
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Rock Drilling ODP (Ocean Drilling Program)
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Iron Meteorites
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Stony Meteorites
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High P & T Experiments
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Seismic Surveys seismic surveys also help us study the subsurface structure of the earth
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Seismic Reflection Studies
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Seismic Studies http://pangea.stanford.edu/~sklemp/ http://www.oceanmarine.com/
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Seismic Studies - Earthquakes
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Seismic Studies - Explosions
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How Do We Learn About the Inner Structure of the Planet? S e i s m c W a v
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Earth consists of a  series of concentric  layers or spheres  which differ in  chemistry  and  physical   properties. Chemical Layers Physical Layers
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Earth's Layered Structure Discovered using changes in seismic wave velocity Mohorovicic discontinuity (“Moho”) Velocity of seismic waves increases abruptly below 5-10 km of depth below ocean floor and 35-60 km depth on continents Separates crust from underlying mantle
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Seismic Studies Differential speed of seismic/sound waves due to density differences Pressure Waves (P) (Fast) Parallel to direction of motion Travel through liquids Shear Waves (S) (Slow) Perpendicular to direction of motion DO NOT travel through fluids (liquid or gas) Seismic waves refract & reflect at density boundaries within Earth
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Layers are Defined by Composition Crust Thin, rocky outer layer Varies in thickness Roughly 7 km in oceanic regions Continental crust averages 35-40 km Exceeds 70 km in some mountainous regions
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Seismology is the study of elastic waves that travel through the earth Two main wave types: Shear waves (S-waves): travel by shearing medium they pass through. S-waves can travel only through solids since particles need to be bonded to each other to propagate wave (similar to a bull whip) Compression waves (P-waves): travel by squeezing and expanding medium they travel through. They can travel through both solids and liquids (e.g., sound waves).
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Reflection and Refraction Seismic waves reflect and refract at the interface between layers within the Earth
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P- and S-Wave Reflection and Refraction P- and S-waves can reflect and/or refract across a variety of Earth’s internal boundaries
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Seismic Wave Travel Times
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Seismic wave speed varies as a function of the density and bulk and shear modulii of the material it is traveling through
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increase in S-wave speed in the strong lithosphere slight decrease in S- wave speed in weak asthenosphere increase in S-wave speed below the asthenosphere in the upper mantle increase in S-wave speed below the 410 km mantle discontinuity increase in S-wave speed below the 660 km upper/lower mantle transition
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Lecture 4 - Earth Structure - Lecture 4 Earth Structure...

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