1. By: R. Wallace, WFHS Modified from D. Garcia, WFHS
Earthquakes
By: R. Wallace, WFHS
Modified from D. Garcia, WFHS

2. Earthquakes and Plate tectonics
The Earth experiences stress due to forces within the Earth.

3. Forces pull and push on the crust.
Folds in sedimentary rocks, Australia
Folds in sedimentary rocks, Australia
Forces pull and push on the crust.
Rocks will bend and stretch to a certain point (elastic limit) and will change shape and volume, move up, down or sideways
When the force is great enough the rocks break, tilt and fold (deformation)
Folds in sedimentary rock in Australia

4. 3 types of stress *All can cause the rocks to fracture or crack.
Compression – squeezes the rocks and pushes them deeper down and higher up.
Tension – pulls on the rocks and cause it to be thinner in the middle and thicker at the ends.
Shearing – pushes rocks into opposite directions causing twisting and tearing.
*All can cause the rocks to fracture or crack.

6. Faulting: a break or crack along which rocks move due to stress
Possible result are earthquakes, landslides, formation of mountains and valleys

7. Faulted rocks Hanging wall – the one part that moves
Foot wall – the block of rock below the fault.

8. Types of Faults Normal Fault At divergent plate boundaries→
Foot wall
Hanging
wall →
Normal Fault
At divergent plate boundaries
Tension acts on the fault and causes the hanging wall to move down relative to the foot wall.
Ex. Sierra Nevadas – (Fault Block Mt: Block of land slides down between 2 normal faults)

9. Types of Faults Reverse fault At convergent plate boundaries
Hanging
wall →
Foot wall →
Reverse fault
At convergent plate boundaries
Compression acts on the fault and causes the hanging wall to move up and over relative to the foot fall.
Ex. Himalaya Mts contain many

10. Types of Faults Thrust fault: A special kind of Reverse Fault
Compression causes the hanging wall to slide over the foot wall

11. Types of Faults Lateral fault (aka Strike Slip)
At transform fault boundaries
Shearing causes blocks of rocks to horizontally slide past each other
Not much up and down motion.
Irregular surface snag each other and twist
Forces build up and the rocks break.

12. End of Part I

13. Earthquake Info
What are Seismic waves? Energy waves that make the ground vibrate during an earthquake.

14. Seismic waves
3 types – primary, secondary and surface
The point in the Earth’s interior where energy is released is the focus. Seismic waves travel outward from the focus.

15. Primary waves (P-waves)
Cause rock particles to move in the same direction as the wave is moving.
Push and pull
compression and stretch

16. Secondary Waves (S-waves)
Move through Earth by causing particles to move at right angles to the direction of the wave. SLOWER!!

17. Surface Waves aka Love waves (L-waves)
The point on the Earth’s surface directly above the focus is the EPICENTER.
Surface waves travel outward from the epicenter moving in an elliptical motion and cause most of the destruction during an earthquake.

18. Discovered in 1911 by A.E.H. Love

19. II. Locating an epicenter
Primary waves are the fastest (and slow down through liquid layers) and secondary waves are slower (stop at liquids).

20. Locating an epicenter

21. Using this information, scientist can determine the epicenter
Using this information, scientist can determine the epicenter. The farther apart the (time between) waves the farther away the epicenter is.

22. This is kind of like how GPS works…

24. STEPS TO DETERMINE EPICENTER
Analyze Richter Magnitude from 3 recording stations.
After it converts to P and S wave graph, get distance.
Where all 3 intersect → Epicenter

25. Mapping Earth’s Interior
The speed and path of seismic waves change at certain depths marking the boundaries of the Earth’s layers.
Seismic waves speed up when they reach the bottom of the crust.
The boundary between the crust and the upper mantle is the Moho discontinuity.

26. TSUNAMI!! Dec 24, 2004 Thailand

27. Measuring Richter (1930s) Mercalli Magnitude (size) of waves 1-10
Biggest reading recorded was in Chile !
Intensity
Compares modern EQ with ones from the past (before Richter scale)
I – XII (1-12)
1886 Charleston X

29. Major Earthquake Zones
The Pacific Ring of Fire - The points surrounding the Pacific Plate where it is subducted under the surrounding plates.
The Mid Ocean Ridge – A series of divergent boundaries
Eurasian Melanesian – A series of convergent boundaries from Europe to SE Asia