EARTHQUAKES

The Way Tectonic Plates Move

Learning Targets:

1. Understand the anatomy of an earthquake – Elastic Rebound Theory

2. Know the types of seismic wavesa) 2 types of Body Wavesb) 2 types of Surface Waves

3. Understand the impacts of tsunamis

Earthquakes

1. Earthquake: a sudden release of energy into the earth’s crust

a) Almost constant small earthquakes

b) 18 per year with 7 or greater magnitude

c) 1 per year with 8 or greater magnitude

Elastic Rebound Theory

1. When stresses build, rocks bend elastically

Elastic Rebound Theory

2. When stresses persist, energy continues to build in the rocks.

Elastic Rebound Theory

3. When the stresses are greater than internal strength of rocks, the rocks snap or fracture.

Elastic Rebound Theory

4. Although the rocks return to their original shape the stresses cause the rocks to move to a new position.

Elastic Rebound Theory

5. This movement releases the energy that was stored in the rocks, which creates an

earthquake

Focus and Epicenter

1. Focus: place where rocks first move

a) Can be anywhere from surface to 200 miles below ground

b) Most earthquakes are shallow (6-10 mi)

2. Why can’t earthquakes happen any deeper?

a) High temperatures makes rocks plastic; no stress builds up

Focus and Epicenter

3. Epicenter: spot on surface above the focus

a) Most shaking happens at epicenterb) Most damage may happen

elsewhere

4. 95% of epicenters are along plate boundaries

a) This is how plate boundaries are drawn

Earthquake Zones

1. Pacific Ring of Firea) ~80% of all earthquakes

2. Mediterranean-Asiatic Belta) ~15% of all earthquakes

3. Other plate boundaries and intraplate

a) ~5%

Transform Plate Boundaries - Shear Stress

1. Shallow earthquakes = more damage

a) A lot of the energy goes to the surface

2. Examples:a) San Andres, Californiab) Dead Sea, Jordanc) Chaman, Pakistand) North Anatolian, Turkeye) Queen Charlotte, Alaska

Convergent Plate Boundaries -Compression Stress

1. Deep earthquakesa) Very powerfulb) Volcanic activity

2. Examples:a) Himalayasb) Aleutian Islandsc) Andesd) Marianas and Mariana trenche) Cascades

Divergent Plate Boundaries Tension Stress

1. Weak, shallow earthquakesa) New crust is thinb) Stress is released frequently

2. Examples:a) Mid-Atlantic ridgeb) Red Sea riftc) East Africa riftd) East Pacific rise

Seismic Waves

1. Earthquake energy travels in seismic waves

2. Study of seismic waves: seismology

3. Body Waves: seismic waves that travel through the interior of the Earth

4. Surface Waves: seismic waves that travel on Earth’s surface

Body Waves – P- & S- Waves

1. P-waves a) P = primaryb) Fastest & first wave to be detectedc) Can travel through solids, liquids,

gasesd) Compression wavese) A lot of power but not much

damage done

Body Waves – P- & S- Waves

1. S-wavesa) S = secondaryb) Slower & second wave to be

detectedc) Motion produces Shear stressd) Only move through solids

because liquids and gases have no shear strength

e) S-shaped

Surface Waves

1. Cause most damage2. Surface waves travel along the

ground outward from an earthquake’s epicenter.

3. Slowest of all seismic waves.

Surface Waves – Love & Rayleigh Waves

1. Love wavesa) Side-to-side motionb) Like a snake

Surface Waves – Love & Rayleigh Waves

1. Rayleigh wavesa) Rolling motionb) Like ocean waves

Tsunamis

1. Caused by underwater earthquakes2. Water is very heavy. One cubic yard

of water weighs almost one ton (2000 lbs)

The Boxing Day tsunami - Geography Video.url

The Boxing Day earthquake.url