Chapter 13.pptx - Earthquakes Slides prepared by Amy...

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Earthquakes! Slides prepared by Amy Williamson Chapter 13
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What is an earthquake? Sudden shaking of the ground caused by the failure of a stressed fault Generated from tectonic stresses acting on rocks. Plate motion drives deformation on faults. Relationship between stress build up and earthquakes (Elastic Rebound Theory)
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Generalized tectonic plate motion
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Elastic Rebound Theory (Harry Reid, 1910)
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Recurrence interval : an estimate of the average amount of time between large earthquakes in a given location or on a given fault Does a rock have the same strength over time? Is stress applied at the same rate over time? Can’t we just predict when an earthquake occurs?
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Rock strength and forces vary over time The amount of stress released by an earthquake can vary as well This means that the recurrence interval is an average time computed over many earthquake cycles
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During an Earthquake
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Earthquake terminology Focus the place within Earth where earthquake waves originate Epicenter Point on the surface , directly above the focus
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Seismic Waves Body Waves (travel through the earth) P-Wave travels fastest and arrive at seismograms first S-Waves are the second waves to arrive at recording stations Surface Waves (travel on the surface of the earth) Last waves to arrive (slowest)
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Primary (P) Waves Push-pull (comP ressional) motion Travel through solid, liquids, and gases Fastest of all earthquake waves ( ~ 5km/s in continental crust)
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Secondary (S) Waves “Up-Down” shearing motion Travel only through solids Slower velocity than P-waves (arrive second at seismometers) ~ 3 km/s in continental crust
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Surface Waves (Rayleigh and Love) Retrograde circular motion (Rayleigh) Side to side motion (Love) ( Just over the surface) Slower than body waves (Slower than P and S waves) RIGHT TOP: Rayleigh Wave RIGHT BOTTOM: Love Wave
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Earthquake Early Warning?
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USGS
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How to measure seismic waves
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Locating Earthquakes Located using: Seismometers at 3 or more locations Difference in P and S wave time for distance
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  • Fall '08
  • INGALLS

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