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Chapter 19 Notes

Chapter 19 Notes. Earthquakes. Stress and Strain. Earthquakes occur when stress builds up and causes movement in the Earth’s crust Compression: squeezing forces Tension: pulling forces Shear: opposing parallel forces/twisting Elastic deformation: initial response to stress

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Chapter 19 Notes

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  1. Chapter 19 Notes Earthquakes

  2. Stress and Strain • Earthquakes occur when stress builds up and causes movement in the Earth’s crust • Compression: squeezing forces • Tension: pulling forces • Shear: opposing parallel forces/twisting • Elastic deformation: initial response to stress • plastic deformation occurs under high stress just before breaking

  3. Faults • Normal fault: produced by tension forces • Reverse fault: produced by compression forces • Strike-slip fault: produced by shear forces

  4. Earthquake Waves • Body Waves • Primary (P-waves): compression waves; move parallel to the direction of wave motion • Secondary (S-waves): transverse waves; move at right angles to the direction of wave motion • Surface waves: move sideways and up and down

  5. Earthquake Waves • P-waves move fastest • Surface waves are slowest, last the longest, and are the most destructive

  6. Earthquake location • Focus: the origin of the EQ waves • Epicenter: “above” the center

  7. Earthquake Measurement • Seismometer: an instrument that records EQ waves • Seismogram: the record of EQ waves

  8. Time travel curves • The difference in arrival time of the P-waves and S-waves can show how far the waves have travelled.

  9. Clues to Earth’s Interior • EQ waves are reflected and refracted in different ways by the different materials inside the Earth

  10. Measuring Earthquakes • Richter Scale: • measures magnitude • energy released • numeric scale (no true upper limit) • Modified Mercalli Scale: • measures intensity • based on the amount of damage • Roman numerals I to XII

  11. Richter Scale

  12. Mercalli Isoseismic Map

  13. Locating an Earthquake • The P-wave and S-wave arrival times determine the distance a station is to an EQ • Three stations are required to locate the epicenter of an EQ

  14. Seismic Belts • Circum-Pacific and Mediterranean-Asian belts

  15. Earthquake Hazards • “Earthquakes don’t kill people, buildings do.” • Structural failures • Brittle building materials cause more damage • Building height oscillations • Land and soil failure • Soil liquefaction • Tsunami • Ocean wave generated by sea floor movement

  16. U.S. Earthquake Risk

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