1. Do First
Questions:
What mechanical layer of the Earth are plates made of?
What mechanical layer of the Earth is moving causing the plates to move?

2. Agenda Quiz on these notes on Thursday Earthquake Notes
Mercalli Scale Practice

3. EARTHQUAKES: WHY? AND HOW?

4. Video

5. What are Earthquakes?
The shaking or trembling caused by the sudden release of energy due to the movements of plates
Usually associated with faulting (movement) or breaking of rocks at plate boundaries

6. Where do Earthquakes occur?
Earthquakes occur along fault lines where two plates meet
Earthquakes can occur at all three types of plate interactions
The most violent earthquakes occur at convergent boundaries
In the US, most earthquakes occur along the San Andreas fault in California
80% of all Earthquakes occur an area of the Pacific Ocean known as the “Ring of Fire”

7. Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur in the circum-Pacific belt
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on spreading ridge centers
more than 150,000 quakes strong enough to be felt are recorded each year

8. http://tinyurl.com/mshzd9f or

9. The Focus and Epicenter of an Earthquake
The focus or hypocenter is the point within Earth where faulting begins
The epicenter is the point directly above the focus on the surface

10. Elastic Rebound Theory
Explains how energy is spread during earthquakes
Rocks on opposite side of the fault are under pressure due to the force and shifting of the plates
Rocks bend until the strength of the rock is exceeded
Rupture occurs and the rocks quickly rebound /return to their original shape
Energy is released in waves that radiate outward from the fault

11. Elastic Rebound Theory

12. Elastic Rebound

13. Seismic Waves Seismic are energy waves released by earthquakes
There are two types:
Body waves
- P and S
Surface waves

14. Seismic Waves

15. Body Waves: P and S waves
Body waves travel through the interior of the Earth
P or primary waves
fastest waves
travel through solids, liquids, or gases
compressional wave, material movement is in the same direction as wave movement
S or secondary waves
slower than P waves
travel through solids only
shear waves - move material perpendicular to wave movement

16. Earthquake Waves P waves move through solids & liquids
Notes: Surface waves cause most damage (“L” waves – feel like ocean waves)
Body waves move through the earth
p & s are Body waves – move through the earth
S waves move through solids only!!!

17. Surface Waves Surface Waves
Travel just below or along the ground’s surface
Slower than body waves; rolling and side-to-side movement
Most destructive type of wave

18. Are you listening? Lets test your understanding!!
Is this a P or an S wave?
P wave!
S Wave
Surface waves cause most damage (“L” waves – feel like ocean waves)
Body waves move through the earth
Surface waves move along surface – not felt opposite side of earth

19. Effects of Earthquakes
Building Collapse
Avalanches and Landslides
Fire
Tsunamis
Liquefaction
occurs when water-logged soil acts like a liquid and causes sections of ground to sink or slide

20. Damage in Oakland, CA, 1989

21. Liquefaction

22. How are Earthquakes Measured?
Seismographs record earthquake waves
Seismograms show:
Amplitude of seismic waves (how much rock moves or vibrates)
Distance to the epicenter
Earthquake direction
Surface waves move along surface – not felt opposite side of earth

23. How Seismographs Work

24. Scales of Measurement 1. Richter Scale 2. Mercalli Scale
Measure the energy released by an earthquake
Measures magnitude using seismic wave data from a seismograph
2.0 to , each increase in number is a 10 times increase
2. Mercalli Scale
Measures the effects of an earthquake
Measures intensity using observation data
I (not felt) to XII (total destruction)

25. MERCALLI VS. RICHTER

26. MERCALLI VS. RICHTER

27. DYL What are two effects of Earthquakes?
Where in the world do most Earthquakes occur?

28. Resources