1. Earthquakes
Chapter 19

2. Earthquakes
Natural vibrations of the ground caused by strain along faults in Earth’s crust
Faults: the fracture or system of fractures along which movement occurs
San Andreas Fault: famous U.S. fault line (California)
N.American plate sliding past Pacific plate

3. Types of Faults Reverse Normal Strike-slip
From compression (convergent boundaries)
Normal
From tension (divergent boundaries)
Strike-slip
From shear (transform boundaries)

4. Types of Faults
Reverse Fault
Strike-slip Fault
Normal Fault

5. Elastic Rebound Theory
When two plate slide past each other, they eventually ‘snag’ on each other and begin to pull.
The ground can only ‘stretch’ so far and when that snag fails, the ground snaps back into place (like a rubber band)

6. Seismic Waves All Earthquakes release seismic waves
3 types of seismic waves:
P-Waves - primary, travel through all material, fastest, back & forth motion
S-Waves - secondary, travel through solids only, 2nd fastest, move up & down
L-Waves - surface, travel along surface, slowest, move back and forth AND up and down

7. Seismic Waves P-waves: S-waves:
S-waves:
L-waves:

8. Seismic Waves Used to determine the Earth’s layers
These waves move through Earth & will only pass through certain materials - tells scientists what’s inside the Earth

9. Locating Earthquakes
Seismometer: machine that picks up Earthquake waves
Because seismic waves travel at different speeds, they arrive at a seismometer at different times
Difference between P and S waves can tell how far away an earthquake occurred

10. Locating Earthquakes
Information from 3 seismometers is needed to plot where an earthquake occurred (triangulation)
Focus: point inside the Earth where the EQ begins/starts
Epicenter: point on the surface of Earth directly above the focus - reported in the news as the location of the EQ

11. Locating Earthquakes

12. Measuring Earthquakes
Richter Scale: measures Earthquake magnitude (energy)
Scale from 1-10
Strongest: 9.5 in Chile (1950)
Mercalli Scale: measures Earthquake intensity (damage)
Scale from I - XII
Used by insurance companies

13. Where do Earthquakes Occur?
Pacific Ring of Fire - 80%
Eurasian Belt - 15%
Mid-Ocean Ridges - 5%
United States
Most occur on West coast
Strongest Quake: St.Louis (1813)

14. Earthquake Hazards
Buildings fall, glass breaks, roads crack, bridges fall
Slope failure (landslides)
Tsunami
Safest place to be:
Away from buildings
In a doorway

15. Earthquake Prediction
Can we predict Earthquakes? NO
Best scientists can do is to say they think one may occur in the next 100 years
California: Parkfield experiences a magnitude 6 earthquake every years - last one was Sept.2004