1. What is an Earthquake? Goal 
Homework 
Demonstrate the different motion of P and S-waves
1.Earthquake Vocab defined
Warm-up Take out last night’s HW, Update TOC, copy down HW
In your journal  Write a brief paragraph that explains in general terms what an earthquake really is. Include the words “plate boundary,” “fault,” and “elastic rebound” in your definition.

2. What are Earthquakes?
The shaking or trembling caused by the sudden release of energy
Usually associated with faulting or breaking of rocks
Continuing adjustment of position results in aftershocks
Near plate boundaries, there are many breaks in the rock called faults. Over time, as the plates gradually get pushed along, more and more pressure builds up at the faults. Elastic rebound occurs when a fault can’t take any more pressure and snaps. We experience this motion as an earthquake.

3. Earthquakes Seismology  Seismologist  study of earthquakes
scientist who studies earthquakes and seismic waves
Keep in mind: Seismologists don’t have to be right near an earthquake to study it. Why is this?
Real-time Data:
World Earthquake Map

4. Earthquake Vocabulary
Fault 
Deformation 
a break in the crust along which plates shift and slip past each other
rocks changing shape due to stress from tectonic motion
Sometimes, rock layers just gradually crunch together and bend.

5. Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur near the Pacific Ocean (Ring of Fire)
most of these result from convergent activity
more than 150,000 quakes strong enough to be felt are recorded each year

6. BREAK Earthquake Vocabulary Elastic rebound 
But if something can’t bend, then it will probably…
BREAK
Elastic rebound 
stress builds up to the point where the rock breaks and snaps back

7. What is the Elastic Rebound?
Explains how energy is stored in rocks
Rocks bend until the strength of the rock is exceeded
Rupture occurs and the rocks quickly rebound to an undeformed shape
Energy is released in waves that radiate outward from the fault

8. Elastic Rebound Elastic Rebound
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
Animation

9. At your table, take one minute to discuss the following:
Seismic Waves
At your table, take one minute to discuss the following:
What are seismic waves? How do they tell us about the interior of the Earth?

10. Seismic Waves
Seismic waves  Earthquake vibrations that travel through the Earth.
Different types of seismic waves travel through the Earth’s layers at different speeds.

11. Seismic Waves
When an earthquake occurs, seismic waves are shot out in all directions:
Some travel across the Earth’s surface (surface waves)
Some travel through the Earth (body waves)
P-waves
S-waves

12. What is a Seismograph? Seismographs
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
Animation

13. What property determines the speed at which seismic waves travel?
Surface wave
Density of the rock

14. Seismic waves travel best through MORE / LESS dense rock layers.
In other words, the vibrations unleashed by earthquakes travel best through…
dense, solid rock.
Surface wave

15. P and S-Waves
Both can be easily demonstrated with a Slinky!

16. Is any domino actually traveling along with the wave?
Seismic Waves
motion of wave
Is any domino actually traveling along with the wave?
Picture the molecules within the rock to be like dominoes knocking into each other.

17. Seismic Wave Motion with Surface Effects
Effects of Seismic Waves
Seismic Wave Motion with Surface Effects
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
Animation

18. Seismic Waves Seismic waves are like sound waves.
They travel best through solids materials.

19. through the entire earth slowest, but most damaging
Seismic Waves
P-waves
S-waves
L-waves
Full name
Where they travel
Relative speed
Type of motion
primary waves
Secondary waves
surface waves
(lateral)
through the entire earth
only through solid
on the earth’s surface
slowest, but most damaging
fastest
slower
up, down, and around
in and out
side to side

20. Earthquake Measurement
Section 5.2:
Earthquake Measurement
Seismogram
(printout of seismic waves)
Seismograph
(measuring instrument)
P-waves first
then S-waves
How do scientists find an earthquake’s start time?
By comparing the arrival times of P and S-waves.

21. Earthquake Epicenter:
Focus 
Epicenter 
Actual point of the shift along the fault (usually miles underground)
Closest point to the focus on the earth’s surface (always directly above the focus)

22. What is an Epicenter?
A point on the surface of the Earth directly above the FOCUS of the earthquake.
The point within the Earth from which earthquake waves originate.

23. Locating the Epicenter:

24. Earthquake Epicenter:
What does the red line in the graph represent?
What does the purple line represent?
Which location is the farthest away from the earthquake’s epicenter?
time/distance of S-waves
time/distance of P-waves
station C

25. Earthquake Epicenter:
4. What is the S-P time interval (ΔT) for
location C?
5. Which location is the closest to the earthquake’s epicenter?
6. How far is station A
from the epicenter?
23 – 12 = 11 minutes
station A
~1,700 km

26. Earthquake Strength 10 10 10 100 4  5  6  7 x 10 x 10 x 10 =
What is the measure of the strength of an earthquake called?
Magnitude
Richter scale 
Based on a factor of _____ for each level.
A magnitude 3 is ____ times as strong as a magnitude 2.
A magnitude 4 is ____ times as strong as a magnitude 3.
A magnitude 4 is _____ times as strong as a magnitude 2.
How much stronger is a magnitude 7 than a magnitude 4?
measures the strength of the ground motion 10 10 10
100
4  5  6  7
x x x =
1,000 times stronger

27. Earthquake Strength and Intensity
Haiti earthquake
What is the difference between this scale and the Modified Mercalli Intensity Scale (MMIS)?
List of greatest magnitude earthquakes

28. Earthquake Damage
Tokyo, Japan: 1923

29. Earthquake Damage
Japan: 2004
Magnitude = 6.6

30. Earthquake Damage
New Zealand: 2010
Magnitude = 7.1

31. Earthquake Damage
Mexico: 2010

32. Earthquake Damage
Oakland, CA: 2007

33. Earthquake Damage
Canterbury, England: 2010
Magnitude = 7.1

34. Earthquake Damage
Anchorage, Alaska: 1964

35. Earthquake Damage
Alaska: 1964

36. You and your partner are now going to practice locating an epicenter through this Power Point.
First you will practice finding Lag Times (the time difference between when P-Waves and S-Waves arrive at recording stations).
Second you will use your Lag Times to find the distance from the station to the epicenter

37. Use the data from the recording stations:
Station A: San Francisco, California
P-Wave arrival 3:02:20 S-Wave arrival 3:06:30
What is the time difference between P and S wave arrivals?
4:10

38. Use the data from the recording stations:
Station B: Denver, Colorado
P-Wave arrival 3:01:40 S-Wave arrival 3:05:00
What is the time difference between P and S wave arrivals?
3:20

39. Use the data from the recording stations:
Station C: Missoula, Montana
P-Wave arrival 3:01:00 S-Wave arrival 3:03:00
What is the time difference between P and S wave arrivals?
2:00

40. Difference in arrival times (LAG TIME):
San Francisco: 4:10 min.
2,800km
Denver, Colorado: 3:20 min.
2,000km
Missoula, Montana: 2:00 min.
1,100km

41. You may have used these is math before!
This is a compass…
You may have used these is math before!
We will be using a compass to draw a circle where the radius of the circle equals the distance from the seismograph to the epicenter.

42. Using the distance from the station to the epicenter:
San Francisco: 4:10
=2,800km
Open your compass to the EXACT distance on the scale.
1,000
2,000
3,000
4,000
5,000

43. . . . Use your carefully set compass to
draw a circle around each city. .
1,100km . .
2,800km
2,000km
You've found
the epicenter!