1 Earthquakes, Tsunamis, and the Oregon Coast When will the next Megaquake occur? Why are tsunamis so destructive? How much of the coast is affected? When will the next Megaquake occur? Why are tsunamis so destructive? How much of the coast is affected?

2 Tsunamis  Sudden shifting of the ocean floor due to earthquakes, volcanic eruptions, and submarine slumping.  open ocean: short heights, long wavelengths (>100 km), and long periods mph!!!  shallow water: their length shortens and their height increases dramatically.  These are NOT tidal waves  Sudden shifting of the ocean floor due to earthquakes, volcanic eruptions, and submarine slumping.  open ocean: short heights, long wavelengths (>100 km), and long periods mph!!!  shallow water: their length shortens and their height increases dramatically.  These are NOT tidal waves

3 Tsunami Animation

4 Sumatra 2004, >275,000 Dead!

5 Before

6 After

7 Courtesy of Mate 3 rd Class Tyler J. Clements/U.S. Navy

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12 Tsunami -- Sea floor deformation

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17 Geologic record in Coastal Estuaries

18 Multiple events recorded in coastal sediments

19 Detective Story Tracking down details of the last big event

20 Records of a tsunami in Japan for which there was no earthquake

21 Stumps of drowned trees revealed by winter storms

22 Tree ring dating Careful dating of the drowned trees correlates with Japanese tsunami

23 Recurrence interval

24 Tsunami risk, PNW

25 Cascadia Core Sites: 1999 = gray, 2002 = yellow Older existing cores = white Washington Channels defined by 8 days of multibeam survey, now classified! Turbidite Paleoseismology: Extending the earthquake record

26 Paleoseismology can address these questions through development of long temporal and spatial histories of past earthquakes This works better in the submarine environment than on land because of continuous sedimentation.

27 Turbidites are easy to capture, but what do they mean?

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29 A time predictable model, over 10,000 years of record, fits the actual recurrence data quite well. This means that if this is correct, we can predict the time, but not the size of the next Cascadia great earthquake, about 200 years from now for a full margin rupture, and overdue for a southern margin rupture.

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31 Know this sign and where to go!

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