1. Aim: How can we explain Earthquakes?

2. What is an Earthquake?
A natural rapid shaking of the lithosphere, due to release of energy stored in rocks
Most caused by movements along faults
Some caused by moving of magma in the lithosphere and with volcanic eruptions

3. Energy stored in rocks is given off as seismic (earthquake) waves.
What are seismic Waves?
Energy stored in rocks is given off as seismic (earthquake) waves.
Scientists study waves to find info about Earth’s interior.

4. Where do earthquakes start?
Earthquake starts at the focus – the point from which the waves are emitted
The location on Earth’s land or water surface directly above the focus is called the epicenter

7. How do we measure earthquakes?
Scientists measure and record earthquake waves using a seismograph

9. What are the different types of Earthquake waves?
3 types of seismic waves are produced AT THE SAME TIME but each behaves differently within earth

10. P-waves (Primary Waves)
Particles vibrate parallel to the direction of movement
Travel the FASTEST
Can pass through solids, liquids, and gases.

13. S-waves (secondary waves)
Particles vibrate perpendicular to the direction they are traveling
Second fastest wave
Can only pass through SOLIDS

16. Surface Waves Produced when a P- or S-wave comes to Earth’s surface.
Travel only on Earth’s solid surface.
Cause much of the surface shaking and damage.

19. Velocity of waves
Depends on properties of materials they are passing through.
Increase density and pressure, increase the speed

20. EARTHQUAKE SHADOW ZONES
At a certain angle from the epicenter both P and S waves disappear
P waves can again be detected beyond a certain point
NO S WAVES EVER APPEAR AGAIN
THE BAND IN WHICH NO WAVES ARE OBSERVED IS CALLED THE EARTHQUAKE’S SHADOW ZONE
However, scientists noticed something unusual. When the angle around the earth’s circumference from the epicenter is more than 102 (This is a distance of about 11,000 kms.) both the P and S waves disappear. Then the P waves can again be detected if the station is more than l43 (l6,000 kms.). NO S WAVE ARE EVER OBSERVED. THE RESULT IS A BAND OF ABOUT 41 OR 4500 KMS. wide in which no waves are observed. This region is called the earthquake’s shadow zone. Location of the shadow zone will depend on the focus of the EQ. Each EQ produces its own shadow zone.

21. EARTHQUAKE SHADOW ZONES
P WAVES DISAPPEAR FROM º -140º
S WAVES DISAPPEAR FROM 105º NEVER TO APPEAR AGAIN

22. Regents Questions

23. The study of how seismic waves change as they travel through Earth has revealed that
Earth’s outer core is liquid because S-waves are not transmitted through this layer
P-waves travel more slowly than S-waves through Earth’s crust
Seismic waves travel more slowly though the mantle because it is very dense
Earth’s outer core is solid because P-waves are not transmitted through this layer

24. What is the direct cause of most earthquakes?
Movement of bedrock along a fault line
Gravitational pull on bedrock by the Moon
Deposition of sediment in lakes and oceans
Heat exchange between the crust and the atmosphere

25. Sometimes faster and sometimes slower
Earthquakes generate P-waves and S-waves. Compared to the speed of the S-waves in a given Earth material, the speed of P-waves is
Always slower
Always faster
Always the same
Sometimes faster and sometimes slower