Tham khảo bài thuyết trình 'geography and oceanography - chapter 6', khoa học tự nhiên, địa lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Earthquakes, Tsunamis, and the Oregon Coast When will the next Megaquake occur? Why are tsunamis so destructive? How much of the coast is affected? Earthquake Zones Plate boundaries -- Spreading ridges -- Collisions -- Sliding Earthquakes require strong, brittle rock Accumulated strain (“elastic”) shallow deep 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 Tsunami Animation Sumatra 2004, >275,000 Dead! Before After Courtesy of Mate 3rd Class Tyler J. Clements/. Navy Japanese Earthquake and Tsunami (March 11, 2011) -- ~18,000 dead video: Tsunami -- Sea floor thrust fault 2004 Sumatra , 1200km fault, 15m slip Mega-Slumps can trigger tsunami Geologic record in Coastal Estuaries Multiple events recorded in coastal sediments Detective Story Tracking down details of the last big event Records of a tsunami in Japan for which there was no earthquake Stumps of drowned trees revealed by winter storms Tree ring dating Careful dating of the drowned trees correlates with Japanese tsunami Recurrence interval Tsunami risk, PNW 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 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. Turbidites are easy to capture, but what do they mean? T19 Cascadia: The Movie This sequence shows the Cascadia Holocene event sequence. The slides are timed at 1 sec = 400 years. Event pulses that correlate at all sites are shown by flashes of the “locked zone” in red. Event “size” shown by intensity of red shading T18 T17a T17 T16a T16 T15 T14b T14 T13 T12a T12 T11 T10R2 T10d T10c T10R1 T10b T10a T10 T9a T9 T8 T7 T6 T5a T5 T4 T3 T2 T1 (AD 1700) A time predictable model, over 10,000 years of record, fits the actual recurrence data quite well. 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. Know this sign and where to go!
