1. NOTES

2. What are Earthquakes? A vibration of Earth’s crust caused by a sudden release of energy Caused by faulting or breaking of rocks Aftershocks – continued re- adjustment of Earth’s crust Foreshocks – small, often precede major e-quakes Usually occur at plate boundaries

3.  Explains how energy is released during an earthquake  Rocks deform or bend  Rocks rupture when pressure accumulates in rocks on either side of a fault and build to a level which exceeds the rocks' strength.  Finally, rocks rebound and return to their original shape when the accumulated pressure is released. Elastic Rebound Theory

4. Rocks rebound to original un- deformed shape Deformation Rupture and release of energy Fence Original position Fault Elastic Rebound Theory

5. Where do earthquakes happen? The point within Earth’s crust where faulting begins is the focus. This is where energy is released. The point directly above the focus on the surface is the epicenter.

6. Where do earthquakes occur? 85% around the Pacific belt 15% around the Mediterranean- Asiatic belt 5% along divergent boundaries and plate interiors  900,000 occur each year  31,000 are strong enough to be felt

7.  Seismology – study of earthquakes  Seismogram – the record of an earthquake  Seismograph – instrument used to record earthquakes (creates seismograms) Studying Earthquakes

8. Seismogram

9. Seismic Waves  Most of the damage and the shaking people feel during an earthquake is from the seismic waves. Two types of seismic waves:  Body waves travel through Earth  Surface waves travel along or just below the surface

10. Body Waves P (Primary) waves –fastest waves –travel through solids, liquids, or gases –compressional wave, material movement is in the same direction as wave movement S (Secondary) waves –slower than P waves –travel through solids only –shear waves - move material perpendicular to wave movement

11. Undisturbed material Focus Surface Primary wave (P-wave) Compression Expansion Undisturbed material Direction of wave movement Secondary wave (S-wave) Wavelength

12. How do seismic wave help us infer Earth’s internal structure?

14. Surface Waves: R and L waves Surface Waves Slower than body waves R (Rayleigh) – rolling motion L (Love) – side-to-side motion Especially damaging to buildings

15. Love wave (L-wave) Undisturbed material Rayleigh wave (R-wave) Rayleigh wave Love wave

16. How is an Earthquake’s Epicenter Located? P waves arrive first, then S waves, then L and R Average speeds for all these waves is known After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter

17. How is an Earthquake’s Epicenter Located? Time-distance graph showing the average travel times for P- and S-waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves

18. Which seismic station is closer to the epicenter? A B

20. How is an Earthquake’s Epicenter Located? Triangulation 3 seismograph stations are needed to locate the epicenter A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter

23. Measuring the Size & Strength of an Earthquake Intensity is a qualitative measurement  Mercalli Scale  Scale of I – XII  Measures damage/sensations

24. Mercalli Scale - Intensity Modified Mercalli Intensity Map –1994 Northridge, CA earthquake, magnitude 6.7

26. Measuring the Size & Strength of an Earthquake Magnitude is a quantitative measurement  Richter Scale  Measures total energy released  Amplitude of largest wave  Exponential scale (30-fold energy increase for each unit)  6.5 releases 30x more energy than 5.5  6.5 releases 900x more energy than 4.5 (30 x 30)  Strongest recorded: 9.5 (Chile 1960) 9.2 (Alaska 1964) 9.1 (Indian Ocean 2004) 9.0 (Japan 2011)

30. The Destructive Effects of Earthquakes  Ground Shaking  The most destructive of all earthquake hazards is ground shaking.  An area's geology, earthquake magnitude, the type of building construction, and duration of shaking determine the amount of damage caused. Fig. 8.13, p. 202, Fig. 8.15, p. 203

31. The Destructive Effects of Earthquakes  Liquefaction occurs when unconsolidated material is saturated with water and it loses its cohesive strength Fig. 8.14, p. 203

32. Liquifaction

33. The Destructive Effects of Earthquakes  Fire occurs when gas and water lines break Geo-inSight 4. and 7., p. 205

34. The Destructive Effects of Earthquakes  Tsunami: seismic sea wave caused by vertical displacement along a fault or an underwater landslide BEFORE AFTER Fig. 8.16, p. 207 2004, a magnitude 9.0 earthquake offshore from Sumatra generated the deadliest tsunami in history

35. Fig. 8-16b, p. 207 Stepped Art

36. Fig. 8.17, p. 208 The Destructive Effects of Earthquakes  Ground Failure – landslides and rock slides are responsible for huge amounts of damage and many deaths.

37. Destructive Effects of Earthquakes  Ground failure can result in building / road collapse Geo-inSight 5. and 6.; p. 205

38. Earthquake Prediction  Seismic risk maps help geologists in determining the likelihood and potential severity of future earthquakes based on the intensity of past earthquakes. Fig. 8.18, p. 209

39. Earthquake Prediction Earthquake Precursors – short-term and long-term changes within the Earth prior to an earthquake that assist in prediction.  Seismic gaps – locked portions of the fault where pressure is building  Surface elevation changes and tilting  Ground water table fluctuations  Anomalous animal behavior Fig. 8.19, p. 210