1. Unit 5: Earthquakes
Mr. Ross Brown

2. What Causes Earthquakes?
Do now: Based on our earlier lessons, what causes earthquakes?

3. In this unit we will learn about:
The relationship between plate tectonics and earthquakes
How scientists locate and measure earthquakes
The ways earthquakes produce so much damage

4. What are Earthquakes? Vibrations in the Earth’s crust
Elastic Rebound Theory: as forces at the fault build up, stress increases. Rocks fracture  earthquake; rocks spring back to original shape

5. What are Earthquakes? Energy radiates outward in seismic waves
These stress other rocks which fracture and result in aftershocks
The area where slippage begins is the focus
The point on the surface directly above the focus is the epicenter

6. What are Earthquakes?

7. How does Focus Location Determine Earthquake Strength?
90% of earthquakes are Shallow-focus
Within 70 km of surface
Result in the most damage
Intermediate ( km deep)
Deep ( km deep)

8. Earthquake Focus Location

9. How does Focus Location Affect Damage from Earthquakes?

10. Aim: How Can We Compare Earthquake Zones?
Turn to page 5 in Reference Tables
Do now: There have been recent earthquakes in Nepal, Chile, and Haiti. Based on what we’ve learned and the chart, how can we compare these locations?

11. What are Major Earthquake Zones?
Pacific Ring of Fire
Mid–Ocean Ridges
Eurasian-Melanesian Belt
European and African/ Indian plates colliding

12. What Causes Fault Zones?
Fault Zone: groups of interconnected faults
At plate boundaries due to stresses when plates:
Subduct
Collide
Separate or Rift
Slide past each other or Strike Slip or Shearing
San Andreas Fault

13. Thought Question
Compare the damage resulting from earthquakes caused by slippage at 300 km to earthquakes caused by slippage at 50 km. Which results in more damage? Why?
Use complete sentences. Treat this like an essay on the Regents exam.

14. Thought Question Explain the Elastic Rebound Theory
What are the four types of plate movements that can cause earthquakes? Use complete sentences.

15. How Likely Is A Major Earthquake In Brooklyn?

16. How do we Detect and Record Earthquakes?
Seismograph
Records vertical motion of the ground
Records horizontal in east-west and north-south
Records as waves on paper or electronically

17. How do Earthquakes Travel?
P (primary) waves and S (secondary) waves
P waves are compression waves, rock moves in the direction of the wave
S waves are shear waves, rock moves perpendicularly to the wave
When these reach the surface, they can be converted to Surface Waves.
Slow moving, like ocean waves on the surface
Rise and fall; VERY destructive

18. Earthquake Waves

19. Thought Question
If a seismograph station measures P waves but no S waves, what can you conclude about the location of the earthquake?

20. How can we locate an earthquake’s epicenter?
Do now: Why is the location of an earthquake’s epicenter important to know?

21. How can we locate an earthquake’s epicenter?

22. How can we locate an earthquake’s epicenter?

23. How can we locate an earthquake’s epicenter?

24. How can we locate an earthquake’s epicenter?
Subtract P wave arrival time from S wave arrival time
Find that difference on the Reference Table

25. How can we locate an earthquake’s epicenter?

26. How do we Measure an Earthquake’s Severity?
Magnitude
The measure of energy released or the amount of ground motion
We used to use the Richter scale, now we use Moment Magnitude Scale
Largest ever: 8.9
Major is 7 or above
An earthquake <2.5 unlikely to be felt

27. How do Earthquakes Cause Damage?
Damage to buildings
Looser soil results in more damage
Tsunamis
Epicenter on ocean floor
Faultingrise or fall of ocean floordisturbs water
Could trigger underwater landslides