1. The Way Tectonic Plates Move
earthquakes
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The Way Tectonic Plates Move

2. Learning Targets:
Understand the anatomy of an earthquake – Elastic Rebound Theory
Know the types of seismic waves
2 types of Body Waves
2 types of Surface Waves
Understand the impacts of tsunamis

3. Earthquakes
Earthquake: a sudden release of energy into the earth’s crust
Almost constant small earthquakes
18 per year with 7 or greater magnitude
1 per year with 8 or greater magnitude
Earthquakes are most often caused by the build up and sudden release of stress caused by the movement of tectonic plates.
Which types of plate boundaries are prone to experiencing earthquakes? Convergent, transform, and divergent plate boundary.

4. Elastic Rebound Theory
When stresses build, rocks bend elastically

5. Elastic Rebound Theory
When stresses persist, energy continues to build in the rocks.

6. Elastic Rebound Theory
When the stresses are greater than internal strength of rocks, the rocks snap or fracture.

7. Elastic Rebound Theory
Although the rocks return to their original shape the stresses cause the rocks to move to a new position.

8. Elastic Rebound Theory
This movement releases the energy that was stored in the rocks, which creates an earthquake

13. Focus and Epicenter Focus: place where rocks first move
Can be anywhere from surface to 200 miles below ground
Most earthquakes are shallow (6-10 mi)
Why can’t earthquakes happen any deeper?
High temperatures makes rocks plastic; no stress builds up
The point where the rock ruptures is usually below the Earth’s surface. The point of rupture is called the earthquake’s focus.

14. Focus and Epicenter Epicenter: spot on surface above the focus
Most shaking happens at epicenter
Most damage may happen elsewhere
95% of epicenters are along plate boundaries
This is how plate boundaries are drawn
Just above the focus on the land surface is the earthquake’s epicenter

15. The point at which rock breaks, causing an earthquake, usually below the Earth’s surface is known as the focus.
The point on the surface of the Earth that is directly above the focus of an earthquake is called the epicenter.

17. Earthquake Zones Pacific Ring of Fire Mediterranean-Asiatic Belt
~80% of all earthquakes
Mediterranean-Asiatic Belt
~15% of all earthquakes
Other plate boundaries and intraplate
~5%

20. Transform Plate Boundaries - Shear Stress
Shallow earthquakes = more damage
A lot of the energy goes to the surface
Examples:
San Andres, California
Dead Sea, Jordan
Chaman, Pakistan
North Anatolian, Turkey
Queen Charlotte, Alaska
Forces that act in opposite but parallel directions causing two materials to slide past one another results in shear stress.

21. Convergent Plate Boundaries - Compression Stress
Deep earthquakes
Very powerful
Volcanic activity
Examples:
Himalayas
Aleutian Islands
Andes
Marianas and Mariana trench
Cascades
The stress that squeezes rocks together is compression.

22. Divergent Plate Boundaries Tension Stress
Weak, shallow earthquakes
New crust is thin
Stress is released frequently
Examples:
Mid-Atlantic ridge
Red Sea rift
East Africa rift
East Pacific rise
Rocks being pulled apart are undergoing tension.

23. Seismic Waves Earthquake energy travels in seismic waves
Study of seismic waves: seismology
Body Waves: seismic waves that travel through the interior of the Earth
Surface Waves: seismic waves that travel on Earth’s surface
Seismic waves that travel along the surface of the Earth are known as surface waves.
Seismic waves that travel through the solid body of the Earth are known as body waves.
Seismo = Earth & -ology = the study of

24. Body Waves – P- & S- Waves
1. P-waves
P = primary
Fastest & first wave to be detected
Can travel through solids, liquids, gases
Compression waves
A lot of power but not much damage done
The fastest and first detected body waves after an earthquake are P-waves.
The slower, more damaging body waves that are detected second after an earthquake are S-waves.

27. Body Waves – P- & S- Waves
S = secondary
Slower & second wave to be detected
Motion produces Shear stress
Only move through solids because liquids and gases have no shear strength
S-shaped
The fastest and first detected body waves after an earthquake are P-waves.
The slower, more damaging body waves that are detected second after an earthquake are S-waves.

30. Surface Waves Cause most damage
Surface waves travel along the ground outward from an earthquake’s epicenter.
Slowest of all seismic waves.

31. Surface Waves – Love & Rayleigh Waves
Love waves
Side-to-side motion
Like a snake

33. Surface Waves – Love & Rayleigh Waves
Rolling motion
Like ocean waves

37. Tsunamis Caused by underwater earthquakes
Water is very heavy. One cubic yard of water weighs almost one ton (2000 lbs)
Underwater earthquakes can result in massive ocean waves called tsunamis.

38. Power of water.

39. Tsunami 1