1. Earthquakes

2. What is an Earthquake?
Earthquakes: Vibrations (seismic waves) within Earth materials -produced by the rapid release of energy
Earth’s crust is in constant motion due to tectonic forces
Earth’s crust can store elastic energy
When forces exceed the elastic limits and structural strength of the rocks, the rocks will break and/or move producing vibrations that travel outward in all directions

3. Earthquakes
The actual place underground where the rocks break producing vibrations is called the focus
The place on the surface directly above the focus is called the epicenter

5. What types of forces are created?
Tension Force:
stretching or pulling force
Makes a normal fault

6. Normal Fault

7. What types of forces are created?
Compression Force:
force pushing something together
Makes a reverse fault

8. Reverse Fault

10. What types of forces are created?
Shear Force:
a system of forces that operates against a body from different sides
Makes a strike-slip fault

11. Strike-Slip Fault

12. What causes Earthquakes?
Movement along faults: energy exceeds the friction holding the sides together and is suddenly released.
Movement of magma (volcanic)
Volcanic eruptions

13. Seismic Waves

14. 3 Types of seismic Waves P waves (primary waves) Compressional wave
Particles move back and forth in the same direction as the wave
Travels the fastest
Can pass through solids and liquids (gases also)
Does not cause damage

15. Types of Waves S wave (secondary wave, shear wave)
Particles move at right angles to the direction of the wave
Travels slower than P waves
Can pass through solids only
Does not cause damage

16. Types of Waves Surface wave Particles move in elliptical orbit
Originates on the surface after the P and S waves go straight up from the focus and reach the surface
The L wave causes the damage and will be the strongest at the epicenter
Travels the slowest

17. How do we Measure Earthquakes?
Earthquake are recorded by a seismograph

18. How do we Measure Earthquakes?
Intensity – a measure of the effects on an earthquake at a particular location
Magnitude: a measure of the strength or amount of energy released during an earthquake

19. How do we Measure Earthquakes?
Richter Scale: Measures the amplitude of earthquake waves on seismograms
Scale from 1-10
Each number is 10 times the amplitude of the number below

23. Earthquake Dangers
Most injuries and deaths are caused by falling objects and most property damage results from fires that start
Tsunami: seismic sea wave sometimes generated when an earthquake originates on the ocean floor

25. Tsunami—December 2004

26. Earthquake Dangers
Landslides