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

5. Focus, Epicenter, and Fault

7. Elastic Rebound Hypothesis

8. Three Types of Faults Strike-Slip Reverse Normal

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

10. Normal Fault

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

12. Reverse Fault

14. 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

15. Strike-Slip Fault

16. 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

17. 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 an 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

18. Seismic Waves

19. 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

20. 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

21. 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

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

24. How Seismographs Work the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

25. Seismograph

26. Seismogram

27. 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

28. 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

31. Measuring Earthquakes 8.2 Measuring Earthquakes  Momentum Magnitude • Derived from the amount of displacement that occurs along the fault zone • Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes. • Measures very large earthquakes

32. Moment Magnitude

33. How are Earthquakes Measured? Mercalli Intensity Scale Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

34. Notable Earthquakes

35. 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 Waves & Earth’s Interior

39. 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

42. Tsunami—December 2004

43. Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

44. 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.

45. 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.

46. Earthquake Dangers • Landslides

47. 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