1. Unit 3: The Dynamic Earth
EarthQuakes!
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: