Earthquakes are caused by the sudden release of energy in the Earth's crust that generates seismic waves. There are three main types of faults that cause earthquakes by movement of tectonic plates. Scientists can measure the location and magnitude of earthquakes using seismographs to detect primary, secondary, and surface seismic waves, then calculating distances based on differences in arrival times of P and S waves at multiple locations. Large earthquakes can trigger tsunamis by displacing large volumes of water.

1. Earthquakes
Liz LaRosa http://www.middleschoolscience.com 2009
for my 5th
grade science class 2009

2. What is an earthquake?
• Used to describe both sudden slip on a fault,
and the resulting ground shaking and radiated
seismic energy caused by the slip
• Caused by volcanic or magmatic activity,
• Caused by other sudden stress changes in the
earth.

3. Three Types of Faults
Strike-Slip
Thrust
Normal

4. What causes earthquakes?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
– Plastic deformation – does not cause earthquakes
– Elastic deformation – rock stretches then reaches
a breaking point, releasing energy.

5. Elastic Rebound – deformed rock goes
back to its original shape
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

6. Focus – point inside the Earth where an
earthquake begins
Epicenter – point on Earth’s surface above focus

7. How Seismographs Work
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
the pendulum remains
fixed as the ground
moves beneath it

8. Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

9. Primary Waves (P Waves)
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

10. Secondary Waves (S Waves)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

11. Comparing Seismic Waves

12. Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive

13. 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

14. Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

15. Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

16. Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

17. How are Earthquakes Measured?
Richter Scale

18. How are Earthquakes Measured?
Mercalli Intensity Scale
Click Link for Interactive Demo
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

19. Earthquake Waves & Earth’s Interior

20. Seismic
Waves in
the Earth
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

21. Tsunamis
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

22. Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

23. Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt