Megathrust Earthquakes Noel Bartlow Splash spring 2010 Earthquakes
Megathrust Earthquakes Noel Bartlow Splash spring 2010
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!
Elastic Waves • Body Waves – P-waves – the fastest wave • P for pressure, or primary – S-waves – slower than Pwaves • S for shear, or secondary • Surface Waves – Love Waves and Rayleigh waves –slower than S-waves – Produce the strongest shaking
Seismographs • Instrument which records how the ground shakes Makes a Seismogram
Plate Tectonics • Two types of plate: Oceanic and Continental • Three types of plate boundaries: – Transform boundaries – Spreading Ridges (divergent boundaries) – Subduction Zones (convergent boundaries)
Subduction Zones • Oceanic plate going underneath continental plate • Ocean trenches • Cause of Megathrust earthquakes
Chile 2010 • Magnitude 8. 8 Megathrust • Rupture length ~400 km • Rupture width ~100 km • 35 km depth
Videos from Chile
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
Tsunami video • • Skip to 5: 40, then 7: 25 http: //www. youtube. com/watch? v=FCWf. Rs 1 fr. YE
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?
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?
Earthquake Engineering • Types of failure: – Pancake – Liquifaction
Videos from Chile Part II http: //www. youtube. com/watch? v=K 7 uagxbi. SGY http: //www. youtube. com/watch? v=m 1 nd. L-Nk 8 WQ
Another Sumatra Tsunami video
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