S6E5e

• What are earthquakes?• What conditions cause earthquakes?• What are some vocabulary words

associated with earthquakes?• How are earthquakes measured?• What are the results of earthquakes?• What does an earthquake feel like?

earthquakes

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http://earthquake.usgs.gov/learn/today/

Today in Earthquake History

http://earthquake.usgs.gov/learn/kids/

Latest Quakes

http://earthquake.usgs.gov/earthquakes/states/georgia/history.php

Georgia EarthquakesClick Past 8-30 days, too

What is an Earthquake?

1. The definition of an earthquake is… a sudden release of tectonic stress along a fault line. They can also result from volcanic activity. Earthquakes create vibrations that cause the breaking of rocks, violent shaking of Earth’s crust, and destruction of buildings.

2. These vibrations move in all directions through the earth. They begin at a point along a fault.

3. A fault is a break in earth’s crust.

How do faults form?

• The earth’s crust is constantly experiencing pressure from forces within and around it. This pressure builds up over time, and eventually causes the crust to break. This becomes a fault.

• Let’s experience it…

Kinds of Faults...

• Faults are divided into three main groups (WORKSHEET TIME!):

4. Normal fault - when two plates are moving apart and one side of the fracture moves below the other; (caused by tension and occur at divergent boundaries!)

5. Reverse fault or thrust fault - when two plates collide and one side of the fracture moves on top of another (caused by compression and occur at convergent boundaries!) A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°.

6. Strike-slip or Lateral (football plays) - when two plates slide past each other horizontally. (caused by shear stress or shearing and occur at transform boundaries!) *Most common fault to cause an earthquake.*

What is an Earthquake?

7. Focus: An earthquake begins along a fault (a crack in the earth’s surface) at a point called the focus.

8. Epicenter: Directly above the focus is a point on the earth’s surface called the epicenter.

*E comes before F so the epicenter is above the focus.*

Where does an earthquake begin?Draw Diagram

EpicenterFocus

9. Seismic WavesWhen the fault ruptures with a sudden movement energy is released that has built up over the years. The energy from an earthquake is released in the form of vibrations called 'seismic waves'… earthquakes! It is actually when these seismic waves reach the surface of the earth that most of the destruction occurs, which we associate with earthquakes.

10. Primary Wave (P-Wave) •First set of waves•Move side to side•FASTEST wave

11. Secondary Wave (S-Wave) •Second set of waves•Also, called a Shear Wave•Move up and down•Travel slow

12. Surface Wave•Move up and down & side to side•MOST DANGEROUS•SLOWEST Wave

Earthquake WavesThree Main Types:

13. Magnitude is a number that characterizes the relative size of earthquakes & is proportional to energy released

Mercalli Scale

What Kind Of Damage Do Earthquakes Cause?

Earthquakes can also cause landslides, sudden eruptions as in the case of a hot lava flow from a volcano

or giant waves called tsunamis. Sometimes new land mass are also formed. Such earthquakes are attributed

with the creation of the greatest undersea mountain range and the longest land mountain range. Liquefaction is also a danger of earthquakes in areas where the soil is

wet or where water is nearby.14. Aftershocks are the small earthquakes that follow a larger one. They are the minor readjustments along the fault after a quake. With time, these small quakes get less and less intense.

15. Liquefaction- When water-saturated soil is shaken in an earthquake, it can behave like a liquid. This is called liquefaction.

• When the soil acts like a liquid, it can cause great damage to the buildings standing on it.

• Liquefaction is what happens to the wet sand at the beach. The sand is hard when you stand on it, but becomes liquid-like when you stick your toes down in it.

*See the cornstarch demonstration*

16. Deformation

• the change in the shape of rock as a result of stress

Folding

17. Folding-the bending of the rock layers from stress is called folding.

18. Anticline-folds that arch up

19. Syncline-folds that sink down

20. Elastic Deformation

- Leads to earthquakes; it is the sudden return of elastically deformed rock to its undeformed shape

• Think of it as a stretched-out rubber band. You can only stretch it so far before it breaks. When it breaks, it releases energy. Then the unbroken pieces return to their original shape.

• (from the textbook)

San Francisco, 1989

San Francisco, 1989

Strongest Earthquakes

• 9.5 Chile, May 22, 1960• 9.2 Indian Ocean (Sumatra tsunami) Dec 26,2004• 9.2 Prince William Sound, Alaska, March 28, 1964• 9.1 Andreanof Islands, Aleutian Islands, Pacific, • March 9, 1957• 9.0 Great East Japan Earthquake and Tsunami, March 13, 2011• 9.0 Kamchatka, Russia, November 4, 1952• 8.8 Off the Coast of Ecuador, January 31, 1906• 8.7 Rat Islands, Aleutian Islands, Pacific,• February 4, 1965• 8.6 India-China Border, August 15, 1950• 8.5 Kamchatka, Russia, February 3, 1923• 8.5 Banda Sea, Indonesia, February 1, 1938• 8.5 Kuril Islands, Pacific, October 13, 1963• http://www.bbc.co.uk/news/world-asia-pacific-12725646

San Francisco, 1989

San Francisco, 1989

…And that was just a 7.2 on the Richter scale!

Haiti 2010

Haiti 2010

...and in the lower 48 states

• In the lower 48 states, there is a tie between the February 1812, New Madrid, Missouri earthquake and the January 1857, Fort Tejon, California earthquake--both magnitude 7.9--for the strongest earthquake recorded.

What does an earthquake feel like?

• Generally, during an earthquake you first will feel a swaying or small jerking motion, then a slight pause, followed by a more intense rolling or jerking motion. The duration of the shaking you feel depends on the earthquake's magnitude, your distance from the epicenter, and the geology of the ground under your feet.

How Long Does an Earthquake Last?

• For minor earthquakes, ground shaking usually lasts only a few seconds.

• Strong shaking from a major earthquake usually lasts less than one minute. For example, shaking in the 1989 magnitude 7.1 Loma Prieta (San Francisco) earthquake lasted 15 seconds;

• For the 1906 magnitude 8.3 San Francisco earthquake it lasted about 40 seconds.

• Shaking for the 1964 magnitude 9.2 Alaska earthquake, however, lasted three minutes.