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Published byWalter Powell Modified over 9 years ago
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Chapter 5: EARTHQUAKES &EARTH’S INTERIOR
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Earthquakes & earthquake hazards Earthquake –Sudden release of energy Seismology –Scientific study of earthquakes & seismic waves Seismic waves –Shock waves traveling out in all directions from earthquake’s source
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Earthquake Hazards & Predictions Primary hazard – ground motion –Collapsing buildings, bridges & other structures –Aftershocks
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Earthquake Hazards &Predictions Secondary hazards –Landslides –Fires –Ground liquefaction –Tsunamis
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Earthquake Hazards &Predictions
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Recent Tsunami –2004 Sumatra –Magnitude 9.1 –~ 30 ft –225,000 casualties –2011 Japan –Magnitude 9.0 –~25 ft. –15,000 casualties
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Earthquake prediction Short-term prediction & early warning –Precursor phenomena –Foreshocks Long-term forecasting Paleoseismology –Study of prehistoric earthquakes
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Earthquake Readiness Mercalli Intensity Scale –Based on observations & damage to structures –Subjective
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The Science of Seismology Seismograph –Instrument to detect & measure vibrations of Earth’s surface Seismogram –Record made by a seismograph
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Seismic waves Body wave –Travels through Earth’s interior Surface wave –Travels along Earth’s surface Focus –Where rupture occurs & earthquake’s energy is first released Epicenter –Point on Earth’s surface directly above earthquake’s focus
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Locating earthquakes P (Primary) or Compressional waves: –Alternating pulses of compression & expansion –Pass through all states of matter S (Secondary) or Shear waves: –Side to side or up &down movement –Pass only through solids –Travel slower than P waves
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Locating earthquakes Surface or L (Love) wave: –Pass around Earth, not through it –Cause most ground shaking & damage –Slower than P & S waves
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Locating earthquakes Finding the epicenter –S – P lag time –Triangulation (3 points needed)
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Measuring Earthquakes Richter Magnitude Scale –Magnitude vs. Intensity –Based on amplitudes of seismic waves shown on seismograph –Logarithmic scale 10 fold increase in amplitude = 1 unit increase 32-fold increase in energy = 1 unit increase
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Measuring Earthquakes Moment Magnitude Scale –Based on rupture size, rock properties, & amount of displacement along fault surface –Used for large earthquakes
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Studying Earth’s Interior Seismic discontinuity –Boundary inside Earth where seismic wave velocities change abruptly
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Studying Earth’s Interior 3 things can happen to seismic waves if they meet a boundary: –Refraction: waves bend as they pass from one material to another –Reflection: some or all of wave energy bounces back –Absorption: some or all of wave energy is blocked
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How geologists look into Earth’s interior Direct observation –Drilling –Xenoliths
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How geologists look into Earth’s interior Indirect observation –Magnetism –Astronomical observations Density –Meteorites
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A Multilayered Planet Crust –Outermost compositional layer of solid Earth, part of lithosphere Lithosphere = brittle & solid –Thickness varies 8 km (oceanic) 45 km (continental) –Moho boundary
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A Multilayered Planet Mantle –Middle compositional layer of Earth, between core & crust –Asthenosphere: mantle where rock is near melting Plastic & weak –Mesosphere –Mantle-core boundary
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Core –Innermost layer Where magnetic field is generated & most geothermal energy resides –Outer core (liquid) –Inner core (solid) A Multilayered Planet
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