Lecture02_Core

# Lecture02_Core - Lecture 2 From core to crust What is the...

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Lecture 2: From core to crust What is the Earth made of, and how do we know? http://rockbox.rutgers.edu/~bemis/PlanetEarth

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The “Hard-Boiled Egg” Earth Crust Mantle Core
We can sample the crust directly …But how do we know what’s beneath?

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How would you attempt to find out what’s in the mantle or the core? Or, for that matter, how thick they are? A. Look at rocks on the surface of the Earth. B. Consider how rocks reflect light. C. Consider how rocks transmit sound. D. Measure variations in gravity from place to place. E. Look at other planetary bodies.
An Introduction to Seismics Earthquakes cause “waves” like shock waves that travel in all directions, even straight through the Earth! Textbook: p. 318-327

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Basic Wave Motion Longitudinal Particle displacement is parallel to the direction of wave propagation Transverse Particle displacement is perpendicular to direction of wave propagation Combination Particles travel in clockwise circles Motion confined to surface All waves can be classified as having either transverse or longitudinal motion or a combination. Note that the wave moves energy not particles – the particles return to (approximately) their original compressional shear surface
Compressional: P (Primary) waves Wavelength is determined by distance between successive pulses of compression

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Shear (S-waves) resemble waves in a rope …wavelength is determined by the distance between successive peaks or troughs
P-waves: can travel through liquids. S-waves (shear) cannot.

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An Introduction to Seismics Seismic rays are perpendicular to wave fronts Seismic rays are reflected & refracted at a “ discontinuity - boundary separating rocks with different densities (velocities).
An Introduction to Seismics P and S waves 1 . Velocity of P & S waves increase with density (= mass/volume). Vary rock type, pressure, temperature 2. P waves slow down in liquids.

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