chapter 19 notes earthquakes. stress and strain earthquakes occur when stress builds up and causes...
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Chapter 19 Notes
Earthquakes
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Stress and Strain
• Earthquakes occur when stress builds up and causes movement in the Earth’s crust
• Compression: squeezing forces• Tension: pulling forces• Shear: opposing parallel forces/twisting• Elastic deformation: initial response to stress• plastic deformation occurs under high stress
just before breaking
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Faults
• Normal fault: produced by tension forces
• Reverse fault: produced by compression forces
• Strike-slip fault: produced by shear forces
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Earthquake Waves
• Body Waves– Primary (P-waves): compression waves; move
parallel to the direction of wave motion– Secondary (S-waves): transverse waves; move at
right angles to the direction of wave motion
• Surface waves: move sideways and up and down
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Earthquake Waves
• P-waves move fastest
• Surface waves are slowest, last the longest, and are the most destructive
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Earthquake location
• Focus: the origin of the EQ waves
• Epicenter: “above” the center
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Earthquake Measurement
• Seismometer: an instrument that records EQ waves
• Seismogram: the record of EQ waves
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Time travel curves
• The difference in arrival time of the P-waves and S-waves can show how far the waves have travelled.
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Clues to Earth’s Interior
• EQ waves are reflected and refracted in different ways by the different materials inside the Earth
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Measuring Earthquakes
• Richter Scale: – measures magnitude – energy released– numeric scale (no true upper limit)
• Modified Mercalli Scale: – measures intensity– based on the amount of damage– Roman numerals I to XII
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Richter Scale
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Mercalli Isoseismic Map
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Locating an Earthquake
• The P-wave and S-wave arrival times determine the distance a station is to an EQ
• Three stations are required to locate the epicenter of an EQ
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Seismic Belts
• Circum-Pacific and Mediterranean-Asian belts
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Earthquake Hazards
• “Earthquakes don’t kill people, buildings do.”• Structural failures– Brittle building materials cause more damage– Building height oscillations
• Land and soil failure– Soil liquefaction
• Tsunami – Ocean wave generated by sea floor movement
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U.S. Earthquake Risk