EAS100 Lecture Notes - Lecture 12: Plate Tectonics, Seismic Wave, Asthenosphere

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EAS 100 Lecture 12 Earthquakes and Tectonics on Planet Earth
Earthquakes and the Earths Interior
Seismic body waves will act differently depending on the density, strength, and rigidity of
material. (same principle as a laser passing through air and then water it appears to bend!)
Denser material allows waves to pass through at higher speeds!
We can use refractions, reflections, and speeds of these seismic waves to gain further
understanding about the composition of Earths interior.
Seismic body waves may:
Reflect needs a sharp boundary to turn it in a different direction
Refract adjustment in direction depending on the contrast in density. Waves may
refract gradually or abruptly. Waves often have an arc-shaped path of motion through
the Earth, as the interior gets progressively denser.
Remember S-waves cannot make it through the outer and inner core as they cannot pass
through liquids, therefore if S-waves make it through the interior of the Earth, they must bend
around the core.
Mohorovicic discontinuity the boundary between the Earths crust and the mantle where we
see a very rapid increase in velocity as we move further down.
Tectonics
The study of movement and deformation of Earths surface and crust.
Made up of plates of lithosphere, NOT plates of crust, that float on the asthenosphere
below. Asthenosphere is more clastic, which allows the more rigid lithosphere to move.
Tectonics is the study of watching these plates move around.
Ex: Explains why the Red Sea is shaped as it is! There is new crust being formed within it, in
hundreds of thousands of years it will likely be a massive sea!
History of Plate Tectonics
Leonardo Da Vinci found fossil sea shells high up in the Italian mountains in 1508, and
was able to deduce that the sea floor must have lifted up somehow
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Document Summary

Eas 100 lecture 12 earthquakes and tectonics on planet earth. We can use refractions, reflections, and speeds of these seismic waves to gain further understanding about the composition of earth"s interior. Seismic body waves may: reflect needs a sharp boundary to turn it in a different direction, refract adjustment in direction depending on the contrast in density. Waves often have an arc-shaped path of motion through the earth, as the interior get"s progressively denser. Remember s-waves cannot make it through the outer and inner core as they cannot pass through liquids, therefore if s-waves make it through the interior of the earth, they must bend around the core. Mohorovicic discontinuity the boundary between the earth"s crust and the mantle where we see a very rapid increase in velocity as we move further down. The study of movement and deformation of earth"s surface and crust: made up of plates of lithosphere, not plates of crust, that float on the asthenosphere below.

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