Structure of the Earth (Learning Outcome)

What are Seismic shadow zones?

They are zone on earth where seismic waves are not detected (no seismic activity is detected)

What did we find out from seismic shadow zones?

Found out that earth had an outer liquid core and a solid inner core

Where are S waves seen?

In the hemisphere where the earthquake occurs

Where can P waves be seen?

They are detected in the hemisphere where the earthquake occurs and on the far side of the planet

Where is the S and P wave shadow zone?

S shadow: It is on the side of the planet that’s opposite to where the earthquake occurs

P shadow: It is the band below mid section of the planet

Describe why there is an S wave shadow zone. What does this reveal about our planet?

This is because S waves are unable to propagate through liquid, therefore, they stop at the core. This reveals that the outer core is liquid

Describe why there is a P wave shadow zone

P waves are able to propagate through a liquid outer core. But when they enter the liquid core they get refracted and bend inwards. They have a lower velocity in liquid outer core than in the mantle. When they exit the liquid outer core, they get refracted again and have P wave energy on the far side of the earth.

What happens if P waves encounter the inner core at a high angle? What does this reveal about our planet? Who discovered this?

The P waves will reflect towards surface of the planet and you can hear very faintly in the shadow zone when they hit the core. This reveals that there is a solid inner core. Inge Lehman who was a woman geoscientist.