1. Earthquake Waves
Chapter 6-2

2. Focus and epicenter Actual location of fault
Up to 700 km below surface

3. Focus and epicenter Surface location directly above the focus
Actual location of fault
Up to 700 km below surface

4. P-waves Primary waves Compression waves
Travel in a horizontal direction
First to arrive at a distant location

5. S-waves Secondary waves - vibrate at right angles to p-wave
- particles move back
and forth but wave
moves forward
- second to arrive at
distant location

6. Surface Waves Surface waves - travel parallel to Earth’s surface
- have greatest height
- move like an ocean
wave
- last to arrive at
distant location
- are responsible for damage

7. Locating Epicenter
Time lag between P-wave and S-wave indicate how far the earthquake is from a seismograph station.
Lag Time

8. Locating Epicenter
The lag time tells us how far we are from an earthquake but not from which direction
Epicenter can be any where on radius of the circle

9. Locating Epicenter
At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake
Infinite number of possible
epicenters

10. Locating Epicenter
At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake
Possible
epicenter
Two seismograph stations narrow possible epicenters down to two
Possible
epicenter

11. Locating Epicenter
At least three seismograph stations are needed to pinpoint the epicenter of an earthquake
epicenter
Three epicenters narrows possible locations down to one

12. DEMO

13. Measuring Earthquakes
Mercalli Scale
- rates earthquake
according to level of
damage at a given
location
- 12 steps to scale
- same earthquake can
have different rating at
different locations

14. Measuring Earthquakes
Richter Scale
- rates earthquake’s
magnitude based
on size of seismic
waves
- works well with
small, nearby
quakes
- waves are
measured by a
seismograph

15. Measuring Earthquakes
Moment Magnitude Scale
- estimates the total
energy released by an
earthquake
- can rate all earthquakes
- scientists look at type
and strength of waves,
amount of movement,
and strength of rocks
that broke

16. Video
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