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Chapter 3

Chapter 3 - Earthquakes.docx

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Environmental Science
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Nick Eyles

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Chapter 3: Earthquakes What Causes Earthquakes? - Earthquake – a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the surface - Seimic Waves – a wave of energy produced by an earthquake - Elastic rebound theory – the sudden release of progressively stored strain in rocks results in movement along a fault 3.1 Indonesia/Sumatra Earthquake and Tsunami, December 26, 2004 – largest earthquake 9.3 Why do Earthquakes cause so much damage? - Focus – the point within the earth from which seismic waves originate in an earthquake - Epicenter – the point on the earth’s surface directly above the focus of an earthquake Body waves – within earth - P wave – a compressional wave (seismic wave) in which rocks vibrate parallel to the direction of the direction of wave propagation - S wave – a seismic wave propagated by a shearing motion, which causes rock to vibrate perpendicular to the direction of wave propagation Surface waves – a seismic wave that travels on the Earth’s surface - Love waves – a type of surface wave that causes the ground to move side to side in a horizontal plane perpendicular to the direction the wave is travelling - Rayleigh waves – a type of surface wave that behaves like a rolling ocean wave and causes the ground to move in an elliptical path How do we know where earthquakes occur? - Seismograph – a seismometer recording device that produces a perm record of earth motion - Seismogram – paper record of earth vibration Determining the location of an earthquake - Travel-time curve – a plot of seismic-wave arrival time against distance - Depth of focus – distance between the focus and the epicenter of an earthquake o Shallow focus : 0-70km deep o Intermediate focus: 70-350km deep o Deep focus: 350-670km deep Measuring the size of an earthquake - Intensity – a measure of an earthquake’s size by its effect on people and buildings - Modified Mercalli scale – scale expressing intensities of earthquakes (judged on amount of damage done) in Roman numerals ranging from I to XII - Magnitude – a measure of the energy released during an earthquake - Richter scale – a numerical scale of earthquake magnitudes - Moment magnitude – an earthquake magnitude calculated from the strength of the rock, surface area of the fault rupture and the amount of rock displacement along the fault What kinds of damage can earthquakes cause? - Ground motion – trembling and shaking of land can cause buildings to vibrate - Fire – broken gas and water mains -
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