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Megathrust Earthquakes

Learn about megathrust earthquakes, elastic waves, plate tectonics, and earthquake engineering. Explore the Chile 2010 and Sumatra 2004 quakes, and the challenges of earthquake prediction and preparedness.

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Megathrust Earthquakes

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  1. Megathrust Earthquakes Noel Bartlow Splash spring 2010

  2. Earthquakes – what are they? • Slip on faults • Elastic Waves make the ground shake • Magnitude – a measure of energy released • Logarithmic scale – a magnitude 8 is 32 times bigger than a magnitude 7, and a magnitude 9 is about 1000 times bigger than a magnitude 7!

  3. Elastic Waves • Body Waves • P-waves – the fastest wave • P for pressure, or primary • S-waves – slower than P-waves • S for shear, or secondary • Surface Waves • Love Waves and Rayleigh waves –slower than S-waves • Produce the strongest shaking

  4. Seismographs • Instrument which records how the ground shakes Makes a Seismogram

  5. Plate Tectonics • Two types of plate: Oceanic and Continental • Three types of plate boundaries: • Transform boundaries • Spreading Ridges (divergent boundaries) • Subduction Zones (convergent boundaries)

  6. Subduction Zones • Oceanic plate going underneath continental plate • Ocean trenches • Cause of Megathrust earthquakes

  7. Chile 2010 • Magnitude 8.8 Megathrust • Rupture length ~400 km • Rupture width ~100 km • 35 km depth

  8. Videos from Chile

  9. Sumatra 2004 • Generated a large, destructive tsunami • Rupture was ~800 km long, 100 km wide • Magnitude 9.1 • Third largest earthquake since 1900, after great Chilean quake of 1960 (9.5) and 1964 Alaska quake(9.2) • 30 km deep

  10. Tsunami video • Skip to 5:40, then 7:25 • http://www.youtube.com/watch?v=FCWfRs1frYE

  11. Earthquake Prediction • Can we predict earthquakes? • Short answer: no • Faults constantly build up strain, then rupture in an earthquake at an unpredictable time • What we can do • Earthquake risk forecast, for 30 or 50 year intervals • Ground motion predictions when the earthquake does happen, how will the ground move?

  12. What can we do about it? • Earthquake Early Warning, Tsunami early warning • Discussion: • What should people do when they hear the alarm or feel shaking? • How well prepared is your home? Your school?

  13. Earthquake Engineering • Types of failure: • Pancake • Liquifaction

  14. Videos from Chile Part II http://www.youtube.com/watch?v=K7uagxbiSGY http://www.youtube.com/watch?v=m1ndL-Nk8WQ

  15. Another Sumatra Tsunami video

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