1. How has seismic study given us a model of earth’s crust and interior?

2. The study of the behavior of seismic waves has led to the development of our model of earth’s crust and interior

3. MOHOROVICIC
In 1909 Mohorovicic studied EQ waves that traveled short distances through the upper part of the lithosphere.

4. WHAT HE FOUND
20-30 km below the continents (different depths in different places) EQ increased their velocity
And
He knew this happened when they went through a more dense material so

5. CONCLUSION There must be a more dense material below the crust.
In fact they called this interface or boundary between the crust and the mantle, the MOHO, after him
Find the Moho on your handy dandy Reference table (pg. 10)

6. Studies of EQ waves gave us more information
The density and chemical composition of the different layers were inferred
ESRT PG 10

7. Sometimes called the M discontinuity it is the boundary between the crust and the mantle

8. The structure of the crust was seen
The crust is thicker under the continents than it is under the oceans however, while thinner the oceanic crust is more dense and more basaltic whereas continental crust is thicker, less dense and more granitic

9. ALSO
Pressure inside earth depends on weight of material lying over a given location- when materials are denser the pressure is millions of times greater
As you go into the earth temperature increases 1degree C for every 100m depth

10. EQ Shadow zone
Zone of the Earth that does not receive any earthquake waves
Between 102 degrees to 143 degrees from an EQ epicenter no P and S waves can be picked up. This is called the EQ shadow zone

11. They then noticed something else

12. THE CORE After 143 degrees we get P waves but no s waves.
Scientists concluded that below the surface of the earth there is a region that has two effects on EQ waves
1) P waves are changed in direction (Deflected) so that they miss the shadow zone and
2) s waves are stopped altogether- from this they inferrred that the outer core is a liquid

13. At 2900 km P waves are slowed and S waves are stopped- They hit the liquid outer core
At 5200 km there is recovery of the P wave velocity- suggests inner core is solid
From the shadow zone earth scientists have calculated that the boundary between the mantle and core is approx 2900 km

14. shadow zone animation
Shadow zone