1. Earthquakes

2. Introductory Clips

3. What is an Earthquake?
Earthquakes: Vibrations (seismic waves) within Earth materials are produced by the rapid release of energy
Earth’s crust is in constant motion because of tectonic forces
Earth’s crust can store elastic energy
When forces exceed the elastic limits and structural strength of the rocks, the rocks will break and/or move producing vibrations that travel outward in all directions

4. Catastrophic Forces—Components & Causes of an Earthquake

5. Earthquakes
The actual place underground where the rocks break producing vibrations is called the focus
The place on the surface directly above the focus is called the epicenter

7. What types of forces are created?
Tension Force:
stretching or pulling force
Makes a normal fault

8. Normal Fault

9. What types of forces are created?
Compression Force:
force pushing something together
Makes a reverse fault

10. Reverse Fault

12. What types of forces are created?
Shear Force:
a system of forces that operates against a body from different sides
Makes a strike-slip fault

13. Strike-Slip Fault

14. What causes Earthquakes?
Movement along faults: occurs when the energy exceeds the friction holding the sides of the fault together and is suddenly released.
Movement of magma (volcanic)
Volcanic eruptions

15. Fault lines & EArthquakes

16. Seismic Waves
Originate at the focus and travel outward in all directions
Foreshocks: small earthquakes that come before a major earthquake
Aftershocks: Are adjustments in the crust after in earthquake
Smaller than main earthquake, but can cause as much or more damage. They can continue for weeks to months. Not every earthquake produces aftershocks

17. Seismic Waves

18. 3 Types of seismic Waves P waves (primary waves) Compressional wave
Particles move back and forth in the same direction as the wave
Travels the fastest
Can pass through solids and liquids (gases also)
Does not cause damage

19. Types of Waves S wave (secondary wave, shear wave)
Particles move at right angles to the direction of the wave
Travels slower than P waves
Can pass through solids only
Does not cause damage

20. Types of Waves L wave (long wave, surface wave, ground wave)
Particles move in elliptical orbit
Originates on the surface after the P and S waves go straight up from the focus and reach the surface
The L wave causes the damage and will be the strongest at the epicenter
Travels the slowest

22. How do we Measure Earthquakes?
Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram

23. How do we Measure Earthquakes?
Intensity – a measure of the effects on an earthquake at a particular location
Magnitude: a measure of the strength or amount of energy released during an earthquake

24. How do we Measure Earthquakes?
Richter Scale: Measures the amplitude of earthquake waves on seismograms
Scale from 1-10
Each number is 10 times the amplitude of the number below

27. Measuring Earthquakes
Locating the epicenter
Lag time between the arrival of the P wave and the S wave to the seismograph station is converted to a distance
A circle with a radius that equals the distance is drawn around the station.
Two stations can narrow down the location to two places where the two circles intersect
Locating the focus: the lag-time of the L wave will determine the depth of the focus
Play Inside Earthquakes clip

29. Earthquake Dangers
Most injuries and deaths are caused by falling objects and most property damage results from fires that start
Tsunami: seismic sea wave sometimes generated when an earthquake originates on the ocean floor

31. Earthquake Dangers Seiche: rhythmic sloshing of small bodies of water
A seiche is the sloshing of a closed body of water from earthquake shaking. Swimming pools often have seiches during earthquakes.

32. Tsunami Clip—Discovery School
BRAINPOP
Tsunami by Brainpop

33. Earthquake Dangers
Liquefaction: unconsolidated materials that are water saturated may turn to a fluid causing some underground objects such as storage tanks to float to the surface
Ground fissures caused by liquefaction near the mouth of the Pajaro River in California during the 1989 Loma Prieta earthquake. When the surface of the ground oscillates, wet, sandy, and muddy soils can flow like a liquid. This is liquefaction. You can liquefy wet sand at the beach by pumping it up and down with your feet. Photo courtesy of the Loma Prieta Collection, Earthquake Engineering Research Center, UC Berkeley.

34. Earthquake Dangers
Landslides

35. Earthquake Safety
Protect yourself from falling objects (GET UNDER SOMETHING) or stand in a hallway or doorway (watch out for a swinging door)
Do not try to go outside during the earthquake
After the earthquake and before the aftershocks, go outside
Do not return to the building until it has been inspected

37. Seismology: The Science of Predicting Earthquakes
Write in your note book the following definition
Seismology: The Science of Predicting Earthquakes