Earthquakes

1. Earthquakes

2. Introductory Clips How Earthquakes work Investigating Earthquakes--San Francisco

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 elasticenergy • 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. 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

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

7. Normal Fault

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

9. Reverse Fault

11. 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

12. Strike-Slip Fault

13. The footwall occurs below the fault • The hanging wall occurs above the fault plane The two sides of a non-vertical fault are known as the hanging wall and footwall.

14. Forces in Earth’s Crust Anticlines and Synclines Compression can cause folds in the crust. Two types of folding are anticlines, which arch up, and synclines, which dip down. A B

15. Folded Mountain

16. Folded Mountain

17. Fault Block Mountains Tension and Normal Faults As tension forces pull the crust apart, two normal faults can form a fault-block mountain range.

19. Fault Block Mountains

20. Fault Block Mountain

21. Forces in Earth’s Crust The Kaibab Plateau Look at the sequence of drawings. In your own words, describe what happens in the last two diagrams.

22. Plateau

23. Plateau

24. 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

25. 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

26. Seismic Waves

27. 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

28. 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

29. 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

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

32. 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

33. 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

36. 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

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

40. Tsunami—December 2004

41. 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.

42. 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.

43. Earthquake Dangers • Landslides

44. 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