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Intro to geology Plate tectonics Minerals Rocks Igneous rocks Volcanism Weathering & erosion

Intro to geology Plate tectonics Minerals Rocks Igneous rocks Volcanism Weathering & erosion Sediments and Sedimentary rocks Metamorphic rocks Rock record and Geologic time Rock deformation 19. Earthquakes 20. Evolution of continents 21. Exploring Earth’s Interior

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Intro to geology Plate tectonics Minerals Rocks Igneous rocks Volcanism Weathering & erosion

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  1. Intro to geology • Plate tectonics • Minerals • Rocks • Igneous rocks • Volcanism • Weathering & erosion • Sediments and Sedimentary rocks • Metamorphic rocks • Rock record and Geologic time • Rock deformation • 19. Earthquakes • 20. Evolution of continents • 21. Exploring Earth’s Interior • 17. Earth beneath the ocean, shorelines • 12. Mass wasting • 13. Hydrologic cycle and Groundwater • 14. Streams • 15. Deserts & winds • 16. Glaciers, Ice Ages • 18. Landscapes • 22. Energy and Mineral Resources • 23. Earth’s environment, Global Change, Human Impacts Where are we? Dynamic motions External factors Resources

  2. CHAPTER 19 Earthquakes • Some recent Earthquakes • What is an Earthquake • Seismology • Locating an Earthquake • Earthquake intensity and magnitude • Earthquake and plate tectonics • Earthquake destruction

  3. Earthquakes : Study questions • Know the definition of an earthquake and how it is related to fault movement • Foreshocks, aftershocks, elastic rebound • What is the difference between earthquake focus and epicenter? • Know the three different kinds of seismic waves, and their characteristic motion, and properties of propagation. • How is an earthquake epicenter located? • Earthquake depth and how they are related to different kinds of plate boundaries and increasing distance from a subduction zone. • Know the Richter magnitude scale and what each unit means with respect to increase in wave amplitude and energy. • Which factors contribute to the destruction caused by earthquakes?

  4. 2) What is an earthquake? Fault - crack in Earth where slip occurs Earthquake – vibration of earth, often caused by slippage along a fault Earthquake focus - fault slip location Epicenter – point on earth’s surface directly above focus From: Tarbuck/Lutgens: Earth

  5. Remember from Ch. 11: Rock deformation Fault definition: a fracture where displacement has occurred: rocks on either side of fault have moved relative to each other.

  6. fault 2) What is an earthquake? • elastic rebound • - plates are continually moving & fault is stuck • - crust starts deforming (stores elastic energy) • fault breaks, releases elastic energy, rock “snaps back” Fig. 19.12

  7. 2) What is an earthquake? aftershocks small earthquakes that follow an initial earthquake in same vicinity foreshocks small earthquakes that sometimes precede a large one by few days See Fig. 19.3

  8. seismic waves ancient Chinese seismograph instrument to record seismic waves 3) Seismology seismology - the study of earthquake “waves”, earthquakes, Earth seismogram- recording of ground shaking from seismographs

  9. Expansion/compression: push/pull motion Shear: side-to-side motion 3) Seismology Types of seismic waves “body waves” P-waves (“P” for primary) S-waves (“S” for secondary) travel in Earth’s interior “surface waves” travel on Earth’s surface Figure Story 19.5

  10. P-wave S-wave Surface-wave 3) Seismology Types of seismic waves Motion produced by the different wave types

  11. fastest Recipe: 1. Measure time between P and S wave on seismogram 2. Use travel-time graph to get distance to epicenter 3. Draw circle on a map with radius of that distance 4. Three or more circles should intersect at EQ! 4) Locating an earthquake P-waves & S-wave travel at different speeds

  12. 4) Locating an earthquake See Fig. 9.16 1. Measure time between P and S wave on seismogram 2. Use travel-time graph to get distance to epicenter 3. Draw circle on a map with radius of that distance 4. Three or more circles should intersect at EQ!

  13. 5) Earthquake Intensity and magnitude • RichterMagnitude • MomentMagnitude • Richter magnitude - concept introduced by Charles Richter in 1935 • Amplitude of the largest seismic wave recorded (P, S, or surface) and distance • Note: Logarithmic scale Fig. 19.7 • Related to physical properties of faulting • Proportional to seismic energy released • Proportional to area of fault break

  14. 5) Earthquake Intensity and magnitude • Large Earthquakes occur less frequently than smaller ones! Fig. 19.8

  15. 5) Earthquake Intensity and magnitude

  16. 6) Earthquake and plate tectonics • recall: fault types (from Ch. 11) See Fig. 19.10

  17. 6) Earthquake and plate tectonics Shallow: Normal faulting, transform faulting, thrust (=reverse) fault Intermediate+ Deep: subduction zones See Fig. 19.13 and 19.12

  18. 7) Earthquake destruction • important factors: Intensity & duration of shaking Soil type (soft? hard rock?) Building design • other effects: Liquifaction Tsunamis

  19. 7) Earthquake destruction • important factors: Intensity & duration of shaking Soil type (soft? hard rock?) Building design • other effects: Liquifaction Tsunamis Seismic hazard map (see Fig. 19.21)

  20. 7) Earthquake destruction • important factors: Intensity & duration of shaking Soil type (soft? hard rock?) Building design • other effects: Liquifaction Tsunamis Fig. 19.18

  21. Earthquakes : A few sample MC What does the elastic rebound theory describe? A. the build-up and release of stress during an earthquake B. the fluctuations in groundwater prior to an earthquake C. the formation of mountain ranges by successive earthquakes D. the uplift of the crust in response to erosion

  22. Earthquakes : A few sample MC What causes the up-and-down wiggles on the seismogram? A. electromagnetic pulses B. ground vibrations C. tsunami waves D. variations in air pressure

  23. Earthquakes : A few sample MC Which of the following correctly lists the order in which seismic waves arrive at a seismograph station? A. P waves  surface waves  S waves B. P waves  S waves  surface waves C. S waves  P waves  surface waves D. surface waves  P waves  S waves

  24. Earthquakes : A few sample MC An earthquake’s Richter magnitude is based on ______. A. the amount of energy released during an earthquake B. the amount of ground movement caused by seismic waves C. the distance between the earthquake and the seismograph station D. the observed effects on people and structures

  25. Earthquakes : A few sample MC The ground motion during a Richter magnitude 8 earthquake is ______ times greater than the ground motion during a Richter magnitude 6 earthquake. A. 2 B. 10 C. 100 D. 1000

  26. Earthquakes : A few sample MC How many seismograph stations are needed to locate the epicenter of an earthquake? A. 1 B. 2 C. 3 D. 4

  27. Earthquakes : A few sample MC Shallow earthquakes, less than 20 km deep, are associated with ___________. A. convergent plate boundaries B. divergent plate boundaries C. transform plate boundaries D. all of the above

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