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

2. Earthquakes
- are vibration of the Earth produced by the release of energy.
- Caused by moving plates at the boundaries.

3. A. Focus - the origin or starting point of the earthquake underground
A. Focus - the origin or starting point of the earthquake underground. Energy is released in all directions.
B. Epicenter – the location on the surface directly above the focus.

4. II. Causes of Earthquakes
Earthquakes are caused by 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. B. 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

7. Closure: Why do most earthquakes cause little damage and loss of life?
Because most occur in
areas that are not
populated.
L.A. Earthquake
Earthquake Destruction

8. AIM: How are Earthquakes Measured?
Do now:
If you were asked to measure a recent Earthquake, what information, observations or data would you use?

9. I. Measuring Earthquakes
Seismology – the study of earthquake waves.
Seismographs –
instruments that
record earthquake
waves. Data is
recorded on a
seismogram.

10. Seismogram/Seismograph

11. Seismogram – a graph produced by recording the ground motion.
*Seismos = shake
* Gramma = what is written

12. Richter Scale: Measures the magnitude (strength) of an earthquake.

13. 2. Moment Magnitude
- estimates the energy released by earthquakes.

14. II. Earthquake Waves A. Surface Waves – are seismic waves
that travel along the Earth’s outer layers.
- These are the most destructive
earthquake waves.

15. B. Body Waves
epicenter
Waves that travel through the Earth’s interior. This includes P and S waves.
These waves help us understand the Earth’s interior

16. 1. P-waves (Primary / Compression Waves)
- Are push-pull waves that compress and expand in the direction that the waves travel.
- Travel through solids, liquids, and gases.
- Have the greatest velocity of all earthquake waves.

17. 2. S- Waves (Secondary / Transverse Waves)
- Shake particles at right angles to the direction that they travel. (up and down)
- Travel only through solids. Cannot go through liquids.
- Slower velocity than P waves.

18. A seismogram records all three types of seismic waves – surface waves, P waves and S waves.
P & S Wave Animation

19. III. Earthquake Zones
About 95% of the major earthquakes occur in a few narrow zones.
Circum-Pacific Belt – the outer edge of the Pacific Ocean (Ring of Fire)
Mediterranean-Asian Belt - Mediterranean Sea

21. Aim: How do we locate Epicenters?
Do Now:
1) From the side table obtain the two tan sheets.
2)Describe the causes of earthquakes.
Earthquakes are caused by the rapid release of energy stored in rock that has been subjected to great forces (at plate boundaries where plates move).
This releases of energy causes the vibrations of an earthquake.

22. I. Locating an Earthquake epicenter
The difference in arrival times of P and S waves provides a way to locate the epicenter.
The greater the time interval between the arrival of the P wave and S wave, the greater the distance to the earthquakes epicenter.
Example:
S-wave - P-wave = 18 sec
B) S-wave - P-wave = 35 sec

23. II. Distance to Epicenter
A) Find the difference in arrival time between the first P wave and the first S wave on the seismogram.
B) Using ESRT page 11 and a piece of scrap paper, find the equivalent distance that matches the difference in time.
S-wave Arrival P-wave Arrival
**ESRT Page 11 and a piece of scrap paper **

24. S-wave – P-wave = 00:04:45 “Spread Technique”
1) Use the time axis to mark off this difference in time. Always use 0 to start.
2) Slide the scrap paper up the chart to match the P and S wave lines with the marks you made.
3) Once they are matched, as close as you can, read down from this intersection to find the equivalent distance.
“Spread Technique”

25. III. P- Wave Travel Time (or s-wave travel time)
Use the distance from the previous step to find the travel time.
- Move up to the wave you are looking for. (either P or S)

26. IV. Origin Time The origin is when the earthquake began. (start)
Subtract the arrival time (P- wave or S- wave) from the travel time (P- wave or S- wave)
Origin (start) Travel Time Arrival (end)

27. 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.