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Earthquakes

Learn what an earthquake is, how faults contribute to earthquakes, different types of earthquake waves, and how scientists measure their intensity and magnitude. Explore the concepts of elastic rebound, fault creep, foreshocks, and aftershocks. Discover how seismographs and seismograms are used to study earthquake waves and how triangulation is used to locate earthquake epicenters.

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Earthquakes

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  1. Earthquakes

  2. What is an Earthquake? • Earthquake—the vibration of Earth produced by the rapid release of energy • Most often caused by slippage along a fault in Earth’s crust • Focus—the zone within Earth where rock displacement produces an earthquake • Produces waves that carry the energy throughout the Earth

  3. What is an Earthquake? • Earthquakes and Faults • A fault is a large fracture in Earth’s crust • Most earthquakes occur along plate boundaries

  4. What is an Earthquake? • Elastic Rebound • 1906 San Francisco Earthquake • San Andreas fault—780 miles • Boundary between the North American plate and the Pacific plate • Pacific plate moved as much as 15 feet northward past the North American plate • Sudden release of stored up energy in rocks that results in movement along a fault—acts like a stretched rubber band

  5. What is an Earthquake? • Fault creep—slow, gradual displacement which occurs relatively smoothly • Some segments regularly slip, producing small earthquakes • Stick-slip—remain locked and store elastic energy for a long time before releasing energy in a great earthquake • Fault scarp—cliff resulting from vertical displacement in which one side is lifted higher in relation to the other

  6. What is an Earthquake? • Foreshocks • Small earthquakes that precede a major earthquake by days or by several years • Aftershocks • Small earthquakes that are the result of adjustment of faults after a major earthquake

  7. Earthquake Waves • Seismology—study of earthquake waves • Seismographs—instruments that record earthquake waves • Seismograms—records from the seismographs

  8. Earthquake Waves • Body waves • P waves (primary waves) • Push/pull • Particles move in the same direction as the waves • Longitudinal • Change volume of intervening material • S waves (secondary waves) • Shake • Particles move at right angles to the waves • Transverse • Change shape of the material that transmits them

  9. Earthquake Waves • Surface waves • Travel along the ground • Moves ground like the ocean tosses a ship • Up and down motion and side to side motion

  10. Finding Earthquake Epicenters • Epicenter—location on the surface of the Earth directly above the focus • Scientists use triangulation to determine the epicenter • Distance of the wave from three different seismic stations

  11. Earthquake Intensity and Magnitude • Mercalli intensity scale • Assesses damage • Strength, distance from the epicenter, nature of surface materials, and building design • Richter scale • Measures magnitude • Amplitude of the largest wave recorded on the seismogram • Logarithmic scale—tenfold increase for every number—30 fold increase in magnitude

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