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Understanding Earthquakes: Causes, Waves, and Impacts

Learn about earthquake phenomena like Elastic Rebound Theory and Seismic Waves, explore Earth's layers, measuring methods, and predicting dangers. Get insights on locating and measuring earthquakes, the Richter scale, and more.

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Understanding Earthquakes: Causes, Waves, and Impacts

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  1. CH 8 Earthquakes • Produced by the rapid release of elastic energy in rock causing vibrations • Elastic Rebound Theory = the rock springs back into it original place • Occur at faults and plate boundaries

  2. Vocab • Focus – point within earth where earthquake originates • Epicenter - point on land surface directly above the focus • Aftershocks – follows the main EQ • Foreshocks – EQs that precede the main earthquake • Seismographs – instrument that records EQ waves • Seismograms – the record made by a seismograph

  3. Earthquake Waves • Primary (P) waves • Body wave, arrives first, fastest, pass through everything, push/pull wave • Secondary (S) waves – • Body wave, arrives second, slower, pass through solids only, sideways/snake wave • Longitudinal (L) waves – • Surface waves, arrive last, liquefy ground, do most damage, up/down wave

  4. Locating an Earthquake • Determined by the difference in arrival times between P and S waves • Know the graph on page 225 • Need at least 3 points to determine the location (triangulation) • EQ zones – circum-Pacific belt and oceanic ridge system

  5. Measuring Earthquakes • Richter scale • Based on size of largest wave • Scale from 1 - 10 • Moment magnitude • More precise • From displacement that occurs along the fault line • Estimates the energy released

  6. Earthquake Destruction • Contributing factors • Intensity of eq • Duration of eq • Foundation of building • Structure/materials of building • Damage prevention • Reinforced concrete • Shock absorbers • Counter weights

  7. Earthquake Dangers • Collapsing structures #1 • Fires #2 • Landslides • Tsunamis • Move fast: 500–950 km/hr (300-600 mph) • Very long wavelengths • Barely noticeable in open ocean

  8. Predicting Earthquakes • Short range prediction are unsuccessful • Long range forecasts are based on the idea that EQs are cyclic. • Land movement • Strain in rocks • Radon gas emissions • Strange animal behavior • Volcanoes • Foreshocks • Seismic gap theory

  9. Earth’s Layers • Earth’s interior consists of 3 major zones (chemical composition) • Crust – thin, rocky outer layer • Oceanic and continental • Mantle – most of earth’s volume • Upper and lower mantle • Core – iron/nickel alloy with extreme pressures • Inner (solid) and outer (liquid)

  10. Earth’s Interior • Lithosphere • Solid and rigid • The crust and upper mantle • Asthenosphere • Softer and flows • Rest of the mantle • Moho Discontinuity • Boundary that separates the crust from mantle • Shadow zone • Know differences between oceanic and continental crust

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