1. Earthquakes, Earth’s Interior and Geologic Hazards
Unit 3: The Dynamic Earth

2. What is an earthquake?
Shaking of the earth’s crust due to a release of energy/pressure along a fault line
Fault: crack in the earth’s crust where there is movement

3. What do earthquakes result from?
Movement along a plate boundary
Volcanic eruptions
Plate: section of the earth’s crust or lithosphere which moves-includes oceanic and continental crust (either, or both)

4. Elastic rebound theory
Explains movement
Says: strain builds up between 2 sections of crust, deforms them. When the stress overcomes friction, crust shifts and goes back to its original shape ( in new place).

5. Earthquake Anatomy Seismic waves: how energy travels through the
Earth from the EQ
Focus: point of origin
Of EQ underground
Earthquake Anatomy
Epicenter: where the EQ
Originates on the surface
focus

6. How do we measure Earthquake strength or magnitude?
Richter Scale- based on powers of ten (log scale), calculated from amplitude of highest S-Wave on seismogram
Measures from 1-10
1=1
2=10x more powerful
3=100x more powerful
How powerful would a magnitude 5 earthquake be then a magnitude 1? Then a 4?
Answer: 10,000 and 10x

8. How do we measure Earthquake Intensity?
Modified Mercalli Scale- based upon peoples observations, ranges from 1-12

10. Seismic Waves: Three types: P,S,L
P wave: primary, compress ional, body wave, travels through solid, liquids, and gases
S-Wave: Secondary, Shear, Transverse, body wave, travels through Solids only
L-wave: Longitudinal, surface wave, (p/s wave converts to this when reaches the surface), two types-Love and Rayleigh Wave

11. Diagram of Body Waves:

12. Diagram of a Surface Wave:

13. Do Now: Copy diagram and label
Earth’s Interior
Do Now: Copy diagram and label

14. What is it like inside the Earth?
Dense
Hot
Solid or liquid depending on the layer
SEE ESRT page 10
Outer core is a liquid,
Inner core is a solid

17. How do we know about the earth’s interior?
From earthquake data
From meteorites
Remember- P waves can travel through everything, S-waves can travel through solids only
Creates a Shadow Zone- 102° to 143° away from the epicenter
The speed of the seismic waves depends on the density of the material- more dense, faster waves
The Moho was discovered this way…

18. http://earthquake. usgs. gov/learn/animations/animation. php

19. Why is there a Shadow Zone?
Earth’s outer core is a liquid and seismic waves cannot travel through this zone.
P-waves are refracted and S-waves cannot travel through this at all.

20. Ring of Fire

22. Ring of Fire
Earthquakes and volcanoes are not distributed randomly- they occur in specific regions- usually along a zone where plate boundaries meet
Ring of Fire-zone along the Pacific Ocean that rings it, where earthquakes and volcanoes are the most common/active

23. Seismic hazards
Tsunamis: giant wave generated by a slip in the earth’s surface and thus an earthquake %20-%20Formation%20of%20a%20Tsunami
Building collapse, fires, water main breaks, gas main breaks result
Liquifaction-occurs when ground saturated with water actually flows like a liquid with intense shaking, occurs with loose sediment

25. Volcanic Hazards Lava, ash is deadly Mudflows or larhars are deadly
Toxic gases
Pyroclastic bombs, explosions are deadly
Cause acid rain
Landslides
Even though violent, lead to fertile soil

27. Seismic Risk Map (USA)