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? 2 Earthquake Zones Plate boundaries Spreading ridges Collisions Sliding Earthquakes require strong, brittle rock Accumulated strain (“elastic”) shallow deep 3 Tsunami  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 400-500 mph!!!  shallow water: their length shortens and their height increases dramatically.  These are NOT tidal waves 4 Tsunami Animation http://nctr.pmel.noaa.gov/animate.html 5 Sumatra 2004, >275,000 Dead! Sumatra 2004, >275,000 Dead! 6 Before 7 After 8 Courtesy of Mate 3 rd Class Tyler J. Clements/U.S. Navy 9 10 . volcanic eruptions, and submarine slumping.  open ocean: short heights, long wavelengths (>100 km), and long periods 40 0-5 00 mph!!!  shallow water: their length shortens and their height. >275,000 Dead! Sumatra 2004, >275,000 Dead! 6 Before 7 After 8 Courtesy of Mate 3 rd Class Tyler J. Clements/U.S. Navy 9 10 11 12 Japanese 8.9 Earthquake and Tsunami (March 11, 2011) ~18,000 dead video:. http://www.youtube.com/watch?v=TRDpTEjumdo 13 14 Tsunami Sea floor thrust fault 2004 Sumatra M9.3, 1200km fault, 15m slip 15 Mega-Slumps can trigger tsunami 16 17 18 19 Geologic record in Coastal Estuaries 20 Multiple events recorded in