Using Earthquakes 1

Using SeismogramsIn the 1800s, seismographs

became more commonplace. Seismograms of a single earthquake could be collected from around the world so they can be carefully inspected.

Using SeismogramsScientists learned some

important facts:1.P-waves are faster than S-waves.

2.S-waves cannot go through fluids.

3.The density of Earth’s material changed (Discovered in 1909 by Mohorovičić. This changes the speed and refracts the wave).

4.The interior of the Earth has a specific structure.

Using SeismogramsScientists noticed that s-waves

never went much past halfway around the globe.

It was known that s-waves could NOT travel through a fluid. Also, material of different density would refract p-waves . . .

. . . so the explanation was easy.

Scientists also noticed that there were wide areas that would never record p-waves. Regardless of how big the quake was.

Using SeismogramsThe Earth has a molten core in its

center!

Because the area always seemed to be at an angle of 110 ̊ away from the earthquake, they calculated how big the core is.

Using SeismogramsThey called this

the shadow zone.

By making a graph of the seismic wave speed vs. the depth of the Earth, scientists were able to see other features.

Using Seismograms

With improved seismographs, we are able to see p and s-waves bouncing off the inside of the Earth!These are called ss or pp-waves when they have reflected once. (ppp-waves for three reflections.)In the shadow-zone, there are no direct p or s-waves, but there are pp, ss, ppp, and sss-waves.P-waves refracting in the core are called k-waves. When they re-emerge, they are called pkp-waves.K-waves that penetrate the solid, inner core are called i-waves.

Using Seismograms

Scientists have re-created how waves move through different types of rock (at different pressures and temperatures) in laboratories.

By comparing these recreations to what is seen from actual seismograms, we have deduced the structures that make up the Earth’s interior.

Using Seismograms

Earth’s LayersEarth’s layers can be viewed in two different ways:• Compositional Layers and • Mechanical Layers

Earth’s LayersCompositional Layers

These are layers divided by what they are made of.–Crust: Made of felsic and mafic rock, 0-65 km deep.–Mantle: Made of liquid and solid rock, 65-2890 km deep.–Core: Made of iron, nickel, and sulfur 2890-6396 km deep.

Earth’s LayersMechanical LayersDivided by how P and S waves move through them.–Lithosphere:

•Crust and top-most part of mantle. Most earthquakes start here P and S waves move through them.

–Asthenosphere:•In the mantle, P and S waves move through them, but will slow down and refract due to material change.

–Mesosphere:•Where the mantle becomes more solid and more dense, P and S waves speed up.

Earth’s LayersMechanical LayersDivided by how P and S waves move through them.–Outer Core:

•Liquid iron, nickel and sulfur. P waves slow down, S waves stop.

– Inner Core:•Solid iron and nickel. P waves speed up and refract due to state change.