Chapter 5: EARTHQUAKES &EARTH’S INTERIOR

1. Chapter 5: EARTHQUAKES &EARTH’S INTERIOR

2. 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

3. Earthquake Hazards & Predictions Primary hazard – ground motion Collapsing buildings, bridges & other structures Aftershocks

4. Earthquake Hazards &Predictions Secondary hazards Landslides Fires Ground liquefaction Tsunamis

5. Earthquake Hazards &Predictions

6. Earthquake Hazards &Predictions • RecentTsunami • 2004 Sumatra • Magnitude 9.1 • ~ 30 ft • 225,000 casualties • 2011 Japan • Magnitude 9.0 • ~25 ft. • 15,000 casualties

7. Earthquake prediction Short-term prediction & early warning Precursor phenomena Foreshocks Long-term forecasting Paleoseismology Study of prehistoric earthquakes

8. Earthquake Readiness Mercalli Intensity Scale Based on observations & damage to structures Subjective

9. The Science of Seismology Seismograph Instrument to detect & measure vibrations of Earth’s surface Seismogram Record made by a seismograph

10. 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

11. Locating earthquakes P (Primary) or Compressionalwaves: 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

12. Locating earthquakes Surface or L (Love) wave: Pass around Earth, not through it Cause most ground shaking & damage Slower than P & S waves

13. Locating earthquakes Finding the epicenter S – P lag time Triangulation (3 points needed)

14. 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

15. Measuring Earthquakes Moment Magnitude Scale Based on rupture size, rock properties, & amount of displacement along fault surface Used for large earthquakes

16. Studying Earth’s Interior Seismic discontinuity Boundary inside Earth where seismic wave velocities change abruptly

17. 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

18. How geologists look into Earth’s interior Direct observation Drilling Xenoliths

19. How geologists look into Earth’s interior Indirect observation Magnetism Astronomical observations Density Meteorites

20. 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

21. 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

22. Core Innermost layer Where magnetic field is generated & most geothermal energy resides Outer core (liquid) Inner core (solid) A Multilayered Planet