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    Earthquake Earthquake Presentation Transcript

    • Earthquake
      • Foci – location inside earth where an earthquake starts
      • Epicenter – Point on earth’s surface directly above the focus
    • Anatomy of Earthquakes
      • Amount of Damage is dependant on depth
      • Foci is close to surface – lots of damage
      • Foci is far from surface – little damage – energy has to travel a long way
    • Seismic waves – p 529
      • 3 Types: P, S, and L
      • L waves – surface waves – roll along the earth’s surface
      • Body waves: P and S waves
      • Body waves travel faster than surface waves- feel p and s waves first after an earthquake
    • Body waves
      • P wave- Primary wave -first to arrive
        • Ground squeezes and streches in the direction of wave travel
        • Travels through solids and liquids
      • S wave- secondary wave -second to arrive
        • Ground is perpendicular (90) to direction of wave travel
        • Travels through solids but not liquids
        • Another name for S-wave is shear wave
    • Smaller amplitude than surface (L) waves, but faster, P arrives first P and S waves
    • Two Types of Surface Waves Most of the destruction Larger amplitude than body waves
    • Why do P waves reach stations before S?
      • Outer core is Liquid – S waves can’t travel through, but p can p 530
    • Surface waves
      • L wave – Travels along the earth’s surface
      • Last to arrive
      • Ground motion is a rolling action like ripples on a pond
    • Seismology
      • Seismometers - instruments that record seismic waves
          • Records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape
    • A seismograph designed to record vertical ground motion The heavy mass doesn’t move much The drum moves
    • Lateral Movement Detector In reality, copper wire coils move around magnets, generating current which is recorded.
      • Seismograms tell :
      • How long an earthquake lasted and the amount of ground shaking
      • Magnitude – rates the strength of an earthquake
      • Higher the magnitude the stronger the earthquake
      • Each 1 step increase in magnitude = 10 times the size of seismic waves
      • Seismograms determine how fast seismic waves are travelling.
      • Look at p531
      • P waves = 5.5 min and S = 10 min
    • Earthquake focus and epicenter
    • Note how much bigger the surface waves are Body Waves Delay between P and S arrivals gives distance to epicenter
    • Graph to find distance to epicenter
      • Don’t need to know the next few slides, but it is cool to do ;)
      • Locating the epicenter of an earthquake
          • Three seismographs needed to locate an epicenter
          • Each station determines the time interval between the arrival of the first P wave and the first S wave at their location
          • A travel-time graph then determines each station’s distance to the epicenter
    • Locating Earthquake Epicenter
      • Locating the epicenter of an earthquake
          • A circle with radius equal to distance to the epicenter is drawn around each station
          • The point where all three circles intersect is the earthquake epicenter
    • Epicenter located using three seismographs
      • Earthquake Belts
      • 95% of energy released by earthquakes originates in narrow zones that wind around the Earth
          • These zones mark of edges of tectonic plates
    • Locations of earthquakes from 1980 to 1990 Broad bands are subduction zone earthquakes, narrow are MOR 80% of seismic energy around Pacific Rim