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Cascadia subduction zone and Mexico City

Cascadia subduction zone and Mexico City. Similar size to the amount of crust that moved during the Sumatra earthquake. Cascade Subduction Zone. Dark red area indicates cooler crust storing energy Lighter red zone could possibly rupture Areas of silent earthquakes?. 1700 Cascadia earthquake.

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Cascadia subduction zone and Mexico City

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  1. Cascadia subduction zone and Mexico City

  2. Similar size to the amount of crust that moved during the Sumatra earthquake. Cascade Subduction Zone

  3. Dark red area indicates cooler crust storing energy Lighter red zone could possibly rupture Areas of silent earthquakes? 1700 Cascadia earthquake

  4. Drop in elevation 1700 Cascadia earthquake 10:57 Vegetation exposed to sea water and dies

  5. Layers of sediment are shaken loose of the continental shelf Deposited on the ocean floor 1700 Cascadia earthquake 19 times in the past 10,000 years

  6. Organic layers are overlain by tsunami deposits 7 cycles the last 3500 years 1700 Cascadia earthquake

  7. Silent earthquakes • Creep events that release large amounts of strain energy without detectable seismic shaking • Last 2-3 weeks, 14.5 month recurrence • A few centimeters at depths 30-50 KM • Equal to Mw 6-7

  8. Movement is detected using Global Positioning Satellite technology Change in movement from compression to extension Silent earthquakes

  9. Silent earthquakes • Significance • Understand how much silent earthquakes reduce overall energy • Large earthquakes every 200-700 years Graph showing slip associated with silent earthquakes

  10. Mexico

  11. Silent earthquakes

  12. Yellow: GPS data Slow slip or silent earthquakes Early- 2002, mid-2006 Red/Green: seismic stations Circled area, earthquakes Silent earthquakes: indicative of earthquakes

  13. Shallow and then becomes more steep under Mexico City Mexican subduction zone

  14. Mexico City Earthquake • 50 x 170 kilometers of displacement along the subduction zone • M 8.1 • Mexico city is 400 kilometers away • City was built on the sediments of Lake Texcoco

  15. Cocos tectonic plate is subducting under the North American Plate Two plates lock Stress builds and energy is stored Stress exceeds frictional force Release of energy in terms of an earthquake Mexican subduction zone

  16. Earthquakes are more shallow than other subduction zones Mexican subduction zone

  17. Mexico City • Drained Lake Texcoco • Clay sedimentary layers • Low frequency surface waves amplified • 1-2 second frequencies • Matched the periods of buildings 6-16 stories

  18. Top floors fail-resonance T-shaped structures Flexible structures between stiff structures Common Building Failures

  19. Hammering Building Failures Soft story collapse

  20. Not all subduction zones are created equally but are capable of producing large earthquakes.

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