1. EARTHQUAKES! Video: Earthquakes 101
Chapter 12

2. Section 1
Earthquakes are caused by a sudden release of energy when rocks move along a fault.
Elastic rebound is thought to cause the rocks to move.

3. Anatomy of an Earthquake
Focus-location of first motion in Earth
Epicenter-spot on surface above the focus
The focus can be shallow or deep
Shallow foci cause the most damage

5. Seismic Waves Body Waves: Travel through the Earth Made up of:
-P waves: primary, fastest
-S waves: secondary, second fastest, travel through solids only

6. Earthquake Waves & Earth’s Interior

7. Seismic Waves and the Earth’s Interior
The speed and direction of seismic waves gives us information about the Earth’s structure
Waves travel at different speeds through different materials
Shadow Zones-areas where no body waves are detected

8. Comparing Seismic Waves

9. Seismic Waves (cont) Surface Waves Slowest moving waves
May cause the greatest damage
2 Types:
-Rayleigh
-Love

11. Earthquakes and Plate Tectonics
Most earthquakes occur at plate boundaries (converging and diverging) where the stress is the greatest

12. How do scientists calculate how far a location is from the epicenter of an earthquake?
Scientists calculate the difference between arrival times of the P waves and S waves
The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

13. How Seismographs or Seismometers Work, TB pg. 217
-measures ground motion and can be used to
determine the distance seismic waves travel
the pendulum remains Video link:
moves beneath it

14. Typical Seismogram- a graphical illustration of EQ waves

15. Locating Earthquakes

16. Locating Earthquakes

17. Locating Earthquakes

18. Section 2 Seismographs record vibrations in the ground
Magnitude: the strength of an earthquake, Richter scale or moment magnitude (more accurate)
Intensity (amount of damage)-modified Mercalli scale-from I-XII

19. How are Earthquakes Measured? Richter Scale

20. How are Earthquakes Measured? Mercalli Intensity Scale
Click Link for Interactive Demo

21. Section 3 Video: Tsunamis 101
Tsunamis can form when the epicenter is on the ocean floor
Damage to structures depends on how they are built and what type of ground they sit on

22. Predicting Earthquakes
No reliable way to predict earthquakes
Scientists are trying to detect changes that occur before an earthquake
Seismic gaps are areas of low earthquake activity, but have a history of strong activity-might be spot for future earthquake
Foreshocks-small earthquakes that precede a large earthquake