1. Earthquakes

2. Warm-up
What other damaging effects can be caused by earthquakes other than the earthquake itself?

3. Earthquakes Mostly caused by plate tectonics
Two plates moving in different directions (usually transverse)
Rock has a lot of friction, so they don’t slide easily
Stress builds over time (energy storage)
Stress is the force acting on a rock over a certain area
When stress overcomes the strength of the rock, movement occurs
The vibrations from this are felt as an earthquake (energy release)

4. Stress
Three kinds:
Compression
Tension
Shear

5. Faults
Fracture in the crust along which the earth moves
3 kinds

6. Reverse fault

7. Normal Fault

8. Strike-Slip Fault

9. Anatomy of an earthquake
Focus:
Where the actual earthquake occurred
Epicenter:
The point on the surface directly above the focus

10. Seismic waves 3 types, all move differently Body waves: Surface waves
Primary
Secondary
Surface waves

11. Primary waves P-waves Push-pull of rock First to arrive
Pass through the interior of the Earth
Can pass through solid rock and liquids (water and molten rock)
Body waves

12. Secondary Waves S-waves Second to arrive
Pass through the interior of the Earth
Only can pass through solids
Body waves

13. Surface Waves Last to arrive to arrive Travel through the surface only
Cause the most damage

14. Seismometer Instruments that measure motion of the ground
Hanging mass (pendulum) stays still while the Earth moves under it
The paper moves and the mass drags a marker across the paper
The bigger the squiggle, the more energy released
Records a seismogram, the graph showing the movement

15. Seismogram

17. Measuring Damage 3 scales: The Richter magnitude scale
The Modified Mercalli Intensity Scale
The moment magnitude scale

18. The Richter magnitude scale
assigns a magnitude number to quantify the size of an earthquake
measured with a seismometer
Measures how powerful it was
Logarithmic scale (meaning each # is 10x worse so a 3 is 10x stronger than a 2 and 100x stronger than a 1)

19. The Modified Mercalli Intensity Scale
The effect of an earthquake on the Earth's surface is called the intensity
 refers to the effects actually experienced at that place (damage assessment)
Non-scientific, but relevant
Very inaccurate judgement of the earthquake itself

21. The moment magnitude scale
Most precise
Measures actual energy released
Based on the area of the fault that moved at the same moment as an earthquake