1. Aim: What is an earthquake?
Do now: In your notes, explain where most earthquakes occur and Why?
Japan

2. Earthquakes
- are vibrations in the crust caused by moving crustal plates.
California

3. Focus - the origin (starting point) of the earthquake underground.
B. Epicenter – the location on the surface directly above the focus.

4. II. Causes of Earthquakes
the release of potential energy stored in rock.
energy is released in all directions

5. A. Elastic Rebound Hypothesis
- Deformation of rocks (stressing/bending) cause them to build up pressure (energy).
- When they break, the stored energy is released which results in the vibrations.

6. III. Measuring Earthquakes
Seismology – the study of earthquake waves (energy).
Seismographs –
instruments that
record earthquake
waves (energy).
*Seismos = earthquake

7. Seismogram – a graph produced by recording the ground motion on a seismograph.

8. Creation of Seismogram

9. Richter Scale: Measures the magnitude (strength) of an earthquake from the seismogram.

10. IV. Types of Seismic Waves (earthquake waves)
epicenter
created at the start of the earthquake.
What do you notice about the waves in the diagram?
wave motion through Earth helps scientists theorize about the inside of Earth and it’s layers.

11. How would you describe the motion of this wave?
A. Body Waves
Travel through the Earth’s interior.
1. P-waves (Primary/Compression Waves)
push-pull waves that compress and expand
the ground in the direction that the waves travel.
How would you describe the motion of this wave?

12. 2. S-Waves (Secondary/Transverse Waves)
move the ground at right angles (up and down)to the direction that they travel.
How would you describe the motion of this wave?

13. P- Wave S-Wave P & S Wave Animation What can this wave travel through?
Travels through
solids and liquids
Travel Faster
Arrives First
Travels through solids, Cannot go through
Liquids
Travel Slower
Arrives Second
How would you describe the speed of this wave?
When does this wave arrive compared to the other?

14. - Most destructive since they are on the surface
B. Surface Waves –seismic waves that travel along the Earth’s outer layers (crust).
- Follow P and S waves
- Most destructive since they are on the surface
China

15. C. Aftershocks and Foreshocks
movements of the crust that follow a major earthquake called aftershocks.
small vibrations called foreshocks come before a major earthquake.
Anchorage, Alaska

16. III. Earthquake Zones
The “Ring of Fire” is the area that surrounds the Pacific Plate which is marked with volcanoes and earthquakes.

17. Closure: Why would someone think that most
earthquakes cause little damage and little
loss of life?
Because most occur in
areas that are not
populated by people or
cities.
Review Book: p #1-10
Tokyo, Japan
Do the questions we did not do.

18. Aim: How do we locate Epicenters?
Based on the diagram, how many seismograph station locations are necessary to find the epicenter of an earthquake?

19. I. Locating an Earthquake Epicenter
The difference in arrival times of P and S waves help locate the epicenter.
The greater the difference, the greater the distance to the earthquakes epicenter.
Take a worksheet from the top bin to practice subtracting P and S wave times.

20. II. Distance to Epicenter (with one wave)
Using the ESRT page 11 we can translate the time into a distance.
… we can also use the same ESRT page to translate a distance into a time.
Examples:
A P-wave takes how long to travel 2600 km?
An S-wave travels how far in 4 min?
After 8 min and 20 sec. a P-wave travels?
An S-wave travels 4.0 x 103 km in…
5 min
1000 km
5000 km
14 min

21. Work on questions 1 - 8 ONLY!
Get an Earthquake P and S wave Travel Time worksheet from the top back bin.
Work on questions ONLY!

22. III. Distance to Epicenter (with two waves)
Where does the difference between the P and S wave exist on this chart?
“Spread Technique”
Ex: S-wave – P-wave = 00:04:45
1) Use the time axis to mark off the difference in time.
2) Match the P and S wave lines with the marks you made.
3) Read down from this intersection to find the equivalent distance.

23. Complete the worksheet

24. IV. P- Wave Travel Time (or s-wave travel time)
Use the distance from the previous step to find the travel time.

25. V. Origin Time The origin is when the earthquake began. (start)
Subtract the arrival time from the travel time
Origin (start) Travel Time Arrival (end)

26. V. Epicenter Location
Data from three or more seismographs must be used to find the exact location of an earthquake epicenter.
Epicenter
- Use the distance to epicenter value and a protractor to draw these circles.

27. Closure:
Looking at the chart on page11 of your ESRT, explain why the difference in travel time between the P and S wave increases as you move further from the epicenter of an earthquake.
- Since the p-wave is faster, it travels farther than the s-wave in the same period of time. This causes the difference in travel time between the two to increase as distance from the epicenter increases.
Review Book: p #1-10