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Chapter 11: Earthquakes

Chapter 11: Earthquakes. Introduction. Earthquake : Vibration of the Earth produced by rapid release of energy Most often caused by slippage along a fault Energy is in the form of waves Focus : AKA Hypocenter Source of earthquake from which energy is released in all directions Epicenter :

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Chapter 11: Earthquakes

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  1. Chapter 11: Earthquakes

  2. Introduction • Earthquake: • Vibration of the Earth produced by rapid release of energy • Most often caused by slippage along a fault • Energy is in the form of waves • Focus: • AKA Hypocenter • Source of earthquake from which energy is released in all directions • Epicenter: • Surface location directly above the focus • Seismometer: • Instrument sensitive to vibrations • Located worldwide & used to measure earthquakes

  3. Focus & Epicenter

  4. Elastic Rebound • Stress applied along pre-existent fault • Stress builds up, straining the rock • Eventually, frictional resistance is overcome • Slippage occurs, releasing the built up strain • Vibrations (earthquake) occur as the rock elastically returns to original shape

  5. Foreshocks & Aftershocks • Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years • Adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks

  6. San Andreas Fault • Best studied fault system • Fault creep: • Slow, gradual displacement • Some segments slip at ~regular intervals • Results in small to moderate quakes • Stick-slip motion: • Storing elastic energy for hundreds of years before rupturing in great earthquakes • Quakes every 50 to 200 years

  7. Seismology • Study of earthquake waves • Dates back 2000 years to the Chinese • Seismographs: • Instruments which record earth’s movement relative to stationary mass • Stationary due to high inertia

  8. Vertical motion Seismographs Horizontal motion

  9. Parts of Waves • Frequency = 1/T • Types of seismic waves: • P-waves • S-waves • Surface waves T

  10. P-waves • Primary waves • Compressional waves ( AKA Push-pull waves) • Travel through liquids & solids

  11. S-waves • Secondary waves • Shake waves • Travel only through solids

  12. Surface Waves • Travel along Earth’s surface • Greatest amplitude, slowest velocity • Cause greatest destruction • AKA Long waves or L-waves

  13. Locating the Source • Epicenter located from difference in arrival time of P-wave and S-wave • Requires seismograms from three locations • AKA Triangulation

  14. Triangulation

  15. Practice Triangulation

  16. Practice Triangulation

  17. Practice Triangulation

  18. Practice Triangulation

  19. Practice Triangulation Luanda 1.2 cm = 1050 km 1.2 cm = x 1050 km distance

  20. Practice Triangulation Luanda 1.2 cm = 1050 km 1.2 cm = x 1050 km distance

  21. Practice Triangulation Luanda 1.2 cm = 1050 km 1.2 cm = x 1050 km distance

  22. Practice Triangulation Luanda 1.2 cm = 1050 km 1.2 cm = x 1050 km distance

  23. Measuring Earthquake Sizes • Intensity Scale • Mercalli Intensity Scale • Based on destruction of buildings • Magnitude Scales • Richter Magnitude (logarithmic) • Based on the Amplitude of the largest seismic wave recorded on seismogram

  24. Mercalli Intensity Scale

  25. Richter Magnitude Scale

  26. Earthquake Destruction • Seismic Vibrations • Tsunami • Landslides & Ground Subsidence • Fire

  27. Formation of Tsunamis

  28. Global Distribution of Earthquakes

  29. Evidence for Plate Tectonics

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