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EARTHSC 2GG3 (199)


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Earth Sciences
Sergei Basik

Tsunami  Tsunami(seismic sea wave) : an abnormally long wavelength wave produced by sudden displacement of water  Near Field Tsunami: tsunami that strikes areas adjacent to its point of origin  Far Field Tsunami: tsunami that strikes areas distant from its point of origin (ex. Indonesia tsunami) (usually bigger and more damaging that near field) Tsunami Wave  Long wavelengths (ex. 400 km long with amp of 50 cm  Velocity dependent of water depth  The wave is so big that there is frictional interaction with the ocean bottom  Eave slows down in shallower water  Wave increases its height as the water become more shallow near the coast  As wave gets closer to shore (shallow)  slows down  increases in height, wall of water Velocity of Tsunami  C= sq rt (gD) C – velocity in metres per second G - gravitational acceleration (9.8) D – Depth in meters  Depends on water depth and gravity  Near shore tsunamis are much slower (112 km/h)  less velocity Run-up Height & Run-out Distance  Storm Surge – not as forceful  Tsunami – forces of waves pushed up making it run up further inland (run-up height of 30-60 m even hundreds of metres) Tsunami Hazards  Lack of warning: difficult to disseminate information btw and within countries (which authorities to call?)  Multiple Waves : time btw waves typically more than 30 min; 2 or 3 waves often worse than first  Contaminated water leading to disease Subduction-Zone Earthquake and Tsunami Creation Steps: 1) ocean plate subducts to continental plate 2) bulge of displaced water 3) bulge releases and waves from this release roar to neares coastline Sumatra Tsunami  9.1 magnitude earthquake in the subduction-zone btw Indian and Burma Plate  3 largest earthquake since 1900  Caused 15-m offset  max you can get  Paleoseismic studies show that giant seismic events occur every 230 years in that area  Tsunami waves generated by the event rose 10m or more above sea level Chile Tsunami  Tsunami laid sediments (TLS) – indicator of tsunami  Microfossils also present which were only found in deep sea areas, topsoil sand deposited by 1960 Subsea Reverse Fault Earthquake and Tsunami Creation  Causes tsunami to go in both directions  Offset in two places  No bulge necessarily like the Sumatra tsunami Volcanic Eruption Tsunami  5% of tsunamis are caused by volcanic eruptions  Collapse of a large volcanic caldera located near sea level can pull a large volume if water and generate a tsunami  Submarine volcanic eruption can drive sea water upward and generate a tsunami  These types of tsunamis impact only the local area while earthquake-generated tsunamis can dis
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