1. Do Now
Describe the last earthquake you can remember. (location, strength, time of day, how it felt, etc.)
Where do earthquakes occur?
Why do earthquakes occur?

2. Earthquakes / Epicenters
Objectives:
Define Elastic Limit
Identify 3 types of fault lines
Differ between P and S waves
Determine shadow zones of P and S waves

3. Where do earthquakes occur?
Occur at plate boundaries
Convergent: Plates move together
Divergent: Plates move apart
Transform: Plates are sliding

4. What Causes Earthquakes
When rock reaches its elastic limit an earthquake occurs.
Elastic Rebound: the sudden “bounce – back” of rock to its original shape
During elastic rebound, rock releases energy. Some of this energy travels as seismic waves that cause earthquakes.

5. Fault Lines When rock breaks, they move along surfaces called faults.
3 Types of faults
Normal
Reverse
Strike/Slip

6. Normal fault Force applied = Tensional
Movement = Rock above fault moves downward.
Before After
What plate boundary is a normal fault similar to?
Divergent

7. Normal Fault
Hanging wall slides below the foot wall.

8. Reverse Fault Force applied = Compressional
Movement = Rock above fault moves Upward.
Before After
What boundary is a reverse fault similar to?
Convergent

9. Reverse Fault Hanging wall slide up passed the foot wall Hanging Wall

10. Strike/Slip fault Force applied = Shearing
Movement = Rocks slide past each other.
Energy builds up until elastic limit is reached = Earthquake
Before After
What boundary is a strike/slip fault similar to?
Transform

11. Strike/Slip Fault Strike/Slip fault show how the fault line will
cause the 2 sides to
not line up.

13. Do Now
Define Elastic Limit
List and describe the 3 types of fault lines
State which applied force creates each type of fault

14. SEISMIC WAVES
When earthquakes occur, waves of energy SEISMIC WAVES travel outward from the earthquake focus
3 types of seismic waves are produced AT THE SAME TIME but each behaves differently within earth.

15. P (Primary) Waves
Primary waves or compression waves vibrate parallel to the direction of movement. (slinky)
Travel faster than any other wave (6-8 km/s)
Travel through solids, liquids, and gases

16. S (Shear) WAVE
Shear wave or secondary waves vibrate back and forth perpendicular to the direction the wave is moving
Slower than P waves (4-5 km/s)
TRAVEL THROUGH SOLIDS ONLY

17. SURFACE OR LONG WAVES
Vibrations travel along earth’s surface in a circular motion at relatively slow speeds (2 km/s) like waves in a pond
Do more damage
because they produce
more ground movement

19. Velocity and seismic waves
Velocity depends on the material they are passing through
Increase density and pressure – greater the velocity
Waves are refracted or bent as waves pass through material with different densities

20. Shadow Zone An area where earthquake waves seem to disappear.
P-Waves can travel through solid, liquid, and gas.
S-waves can travel through SOLID ONLY!
P-Waves enter liquid outer core = Wave slows down!
S-Waves enter liquid core = Waves disappear.

21. Shadow Zone
S-Waves do not make it through. Cant travel through liquid outer core.

22. P Wave and S Wave Chart / Locating Epicenters
Objectives:
Analyze P and S wave chart
Determine travel times of seismic Waves
Analyze seismograms
Locate epicenters

23. Determining distance to Epicenter
Epicenter – The location of an earthquake on the surface of the Earth above the focus.
Focus – Location within the Earth’s crust where the breaking of rock occurs
Surface

24. Seismograph / Seismogram
Geologist use an instrument to measure seismic waves called a seismograph.
Measures the arrival times of the P-Wave, S-Wave, and Surface Wave.
Which wave will always arrive first???
P (Primary) Wave = Faster Speed

26. P – S Wave Chart
Chart can be used to determine arrival times of P and S waves.
Can also be used to locate the distance to the epicenter from the seismic station.

27. This represents TIME (in minutes!)
Notice the vertical axis
This represents TIME (in minutes!)
Let’s enlarge a small section

28. 20 Between each minute, we notice that there are 3 segments.
If there are 60 seconds in a minute, each one of these segments must be ________seconds. 20

29. What would this time be?
2 minutes, 20 seconds

30. This represents DISTANCE (in thousands of Kilometers!)
Notice the horizontal axis
This represents DISTANCE (in thousands of Kilometers!)
Let’s enlarge a small section

31. So what would this distance be?
1,000km
2,000km
1,200km
1,400km
1,600km
1,800km
So what would this distance be?
Fill these in...
5,400km

32. There are also two curves on this chart that display the way different earthquake waves behave.

33. S-Wave
P-Wave

34. This chart can be used for answering many different questions!
Let's try a few examples
How long does it take an S-Wave to travel 5,000km?
Go to the chart!

36. Another example... Go to the chart!
The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be?
Go to the chart!

37. 3,600km

38. Another example... Go to the chart!
I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be?
Go to the chart!

39. Slide your scrap paper up until the tick marks match up with the curves…
Mark off 7 minutes on scrap paper…

40. LOCATING THE EPICENTER OF AN EARTHQUAKE
The difference in travel time between P and S waves can be used to determine the DISTANCE from a station to the epicenter
The farther the station , The longer the travel time.
TO DETERMINE THE EXACT LOCATION OF AN EPICENTER, you must have 3 seismic stations recording the same earthquake

41. Locating an Epicenter
Station A
Station C
Epicenter
Station B

42. Collecting data from the recording stations:
Station A: San Francisco, California
P-Wave arrival 3:02:20 S-Wave arrival 3:06:30
4:10

43. Collecting 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

44. Collecting 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

45. Find the distance to the epicenter for each station.
Using the P and S wave chart, Find the distance from each station to the epicenter.
San Francisco: 4:10
2,800km
Denver, Colorado: 3:20
2,200km
Missoula, Montana 2:00
1100km

46. Recording Board Difference in arrival times:
San Francisco: 41:0
2,800km
Open your compass to the EXACT distance on the scale.
1,000
2,000
3,000
4,000
5,000

47. . . . Use your carefully set compass to
draw a circle around each seismic station. . . .

48. How are earthquakes measured?
Seismographs measure an earthquakes Magnitude – The amount of energy released.
The Richter Scale measure local intensity. Describes how much energy is released.

50. Tsunamis
Tsunamis – Ocean waves caused by seismic waves.