1. Earthquakes and Seismic Waves
6th Grade: Section 2 Chapter 2

2. Review: Forces in the Earth’s Crust
Shearing is the movement that happens to the crust along a Transform Boundary
Tension is the movement that happens to the crust along a Divergent Boundary
Compression is the movement that happens to the crust along a Convergent Boundary

3. What are the 3 types of faults we have studied?
Normal Fault:
occurs when plates diverge
results from tension
The hanging wall slips below the footwall
Reverse Fault:
Occurs when plates converge
Results from compression
The hanging wall moves up above the footwall
Strike-slip Fault:
Occurs when plates slip past each other
Results from shearing
Sideways motion, not up and down

4. Where do Earthquakes come from?
PLATE TECTONICS!
When plates move and create faults, the force exerted on the crust (compression, tension, or shearing) creates Earthquakes

5. What is the definition of an Earthquake?
The shaking and trembling that results from tectonic plates shifting, causing rocks to break along fault lines and releasing energy throughout the earth’s interior.

6. What are the components of an Earthquake?
Focus: the area within the Earth’s lithosphere where the rock breaks, triggering the Earthquake
Epicenter: the point on the Earth’s surface directly above the focus

7. Earthquake components: Seismic Waves
Seismic Waves: the vibrations traveling through the Earth that carry the energy released during an Earthquake
3 types of Seismic Waves:
P waves (primary)
S waves (secondary)
Surface waves

8. Seismic Waves
P waves: seismic waves that compress and expand like an accordion
S waves: seismic waves that vibrate from side to side as well as up and down
Surface waves: when p and s waves reach the epicenter, and move across the surface of the Earth in the motion of waves like the ocean

9. P-wave motion: S-wave motion:
Waves in the Earth’s Interior: Slinky Demonstration:
P-wave motion:
They move the fastest and can move through solids and liquids
Can damage buildings when they reach the surface
S-wave motion:
Move more slowly than P waves
Cannot move through liquids

10. Common Questions after Earthquakes:
“How big was the quake?”
“Where was the earthquake centered?”

11. Measuring Earthquakes
1) Mercalli scale
2) Richter scale
3) Moment Magnitude Scale

12. Measuring Earthquakes
Mercalli Scale: 12 step rating based on how much damage the earthquake causes on the surface of the Earth
The same earthquake can have different ratings at different locations
--uses Roman numerals: I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII

13. Mercalli Scale:
I-III: People notice vibrations like those from a passing truck
IV-VI: Slight damage. People run outdoors.
VII-IX: Moderate to heavy damage. Buildings jolted off foundations or destroyed
X-XII: Great destruction. Cracks appear in the ground. Waves seen on the surface.

14. Measuring Earthquakes
The Richter Scale: a measurement of an earthquake’s magnitude (the size of the waves)
Scientists assign a magnitude by measuring an earthquake’s seismic waves
Scientists use a SEISMOGRAPH to measure the seismic waves on a Richter Scale
Provides accurate measurements for small, nearby earthquakes. But does not work well for large or distant earthquakes

15. Measuring Earthquakes
Moment Magnitude Scale:
Estimates the total energy released by an Earthquake
Measure the magnitude of the seismic waves, the strength of the rocks that broke, the distance that the fault slipped

16. Canterbury, Sept.4, 2010 magnitude= 7.1

17. Myanmar, March 25th 2011 magnitude 6.8

18. Virginia August 23 2011 magnitude 5.8

19. Great Chilean Earthquake: 1960, magnitude= 9.5

20. Magnitude: tells how much energy was released by the earthquake
Each one point increase in magnitude represents a release of 32 times as much energy
Earthquake with a magnitude of 5 releases 32 times as much energy as an earthquake with a magnitude of 4