Chapter 10: Earthquakes (Study Guide) – Flashcards
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How do we know about Earth's internal layers?
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Waves refract and reflect at boundaries
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How was the Moho discovered?
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Seismic waves travel faster through the mantle than through the crust. Seismic-velocity discontinuities define boundaries in the mantle.
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Earthquake
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A vibration caused by the sudden breaking or frictional slip on a fault (release of elastic energy) and the resulting ground shaking and radiated seismic energy caused by the slip
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What causes earthquakes?
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Sudden formation of a new fault, sudden slip on an existing fault, phase change, movement of magma, landslide or meteorite impact
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Where do earthquakes occur?
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Seismic belts/zones that coincide with plate boundaries (plate-boundary earthquakes); earthquakes that occur outside this zone are intraplate earthquakes. Happen between top 60km and 660 km of the Earth.
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What six hazards are associated with earthquakes?
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Groundshaking/displacement, landslides, tsunamis, fires, liquefaction, flooding
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P-Waves
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Compressional seismic waves that move through the body of the Earth. Primary wave; pressure or compressional wave (i.e. pushing/pulling a slinky). Travel fast through liquid and solid. Parallel.
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S-Waves
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Seismic shear waves that pass through the body of the Earth. Secondary wave; shear wave. Particles are moved up and down to propagate the wave (i.e. flicking a rope). Travel slow through only solids. Perpendicular.
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Body Waves
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P-Waves and S-Waves
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Surface Waves
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Seismic waves that travel across Earth's surface. Slow but destructive and produce the most damage. Lower frequency and decay more slowly, cause tall buildings to vibrate more.
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Love Waves
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Surface wave that are ripple/snake-like
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Rayleigh Waves
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Surface wave that ripple up and down
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How can seismologists pinpoint the location of an earthquake from seismographs?
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P-Waves travel faster than S-Waves; the interval between their time travel curve increases with distance. By matching the observed interval to the curves, the distance from the station to the epicenter can be found. S-P time indicates how far away the earthquake was. Must have distance of earthquake from three stations.
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Recurrence Interval
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The average time between earthquake events
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Slip Rate
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The average rate at which one side of the fault moves with respect to the other side
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Slip Rate Formula
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Slip Rate: Average slip per rupture/Recurrence interval
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Seismic Gap
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Places that haven't slipped recently; likely earthquake candidate if stress is building up on the locked portion of the fault, waiting to be released by a future major earthquake
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Induced Seismicity
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Seismic events caused by the actions of people. Commonly caused by waste-water injection, not fracking
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What is the relationship between earthquake magnitude and energy released by the earthquake?
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The higher the magnitude, the greater the energy released
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What is the relationship between earthquake magnitude and the amount of shaking felt near the epicenter of the earth?
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The higher the magnitude, the more intense the shaking near the epicenter of the quake
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What is the relationship between earthquake magnitude and how long shaking lasts?
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The higher the magnitude, the larger the fault area, the longer the duration of the earthquake, the longer the shaking lasts
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What is the relationship between earthquake magnitude and how often that size earthquake occurs worldwide?
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The higher the magnitude, the less frequently it occurs
