1. Earthquakes

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 sudden stress changes in the earth.
Usually occur at or near plate boundaries
Some are strong and can be felt on the surface, some are weak and can only be felt by a seismograph

3. Three Types of Faults Strike-Slip Reverse Normal Three types of faults
Form depending on type of plate motion and complex reaction of earth’s lithospheric blocks
Strike-slip
Normal
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

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

7. How Seismographs Work
the pendulum remains fixed as the ground moves beneath it

8. Typical Seismogram

9. Earthquake Vocabulary
Seismology – The study of earthquakes
Seismograph – An instrument that records vibrations in the ground and determines the location and strength of an earthquake
Seismologist – A person who studies earthquakes
Seismic Wave – A wave of energy that travels through the Earth and away from an earthquake in all directions
Seismogram – a tracing of earthquake motion that is created by a seismograph

10. Primary Waves (P Waves)
A type of seismic wave that compresses and expands the ground
The first wave to arrive at a seismograph

11. Secondary Waves (S Waves)
A type of seismic wave that moves the ground up and down or side to side

12. Comparing Seismic Waves

13. 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

14. 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

15. Locating Earthquakes

16. Locating Earthquakes

17. Locating Earthquakes

18. How are Earthquakes Measured? Richter Scale

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

20. Earthquake Waves & Earth’s Interior

21. Seismic Waves in the Earth