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

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

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

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

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)

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

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

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

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

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

They then noticed something else

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

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

shadow zone animation Shadow zone