New tsunami forecast for the Atlantic CoastlineOk, I give, that image isn’t a tsunami, that’s the st

New tsunami forecast for the Atlantic CoastlineOk, I give, that image isn’t a tsunami, that’s the storm surge from Hurricane Sandy pouring into Brooklyn, New York in 2012 (with the Manhattan Bridge in the background). But, aside from the fact that a tsunami probably wouldn’t leave that fence standing, the storm surge of Hurricane Sandy showed just how vulnerable the cities on the Atlantic coast are to rising water.When most people on the Atlantic Coast think of flooding, they think of hurricanes. After all, it just happened. But, over 80 years ago on the coast of Canada, there was a different kind of flood. It was local, but an area of the Grand Banks was hit in 1929 with a tsunami that left thousands of people homeless and killed nearly 30 people.Tsunamis are much more common in the Pacific and Indian oceans where there are subduction zones. In a large subduction zone earthquake, part of the earth’s crust itself rises upwards, pushing up the water on top of it and generating a gigantic wave as the uplifted water rushes away. The Atlantic Ocean doesn’t have subduction zones; it can’t generate tsunami like this, so what happened in 1929?Well, there was an earthquake in 1929 that set off this tsunami, a magnitude 7.3 event, but it wasn’t a subduction earthquake, it was a strike-slip earthquake. This is the same type of earthquake that happens along the San Andreas Fault; 2 plates gliding past each other, but none of them moved upwards.One other factor is required to generate this tsunami; an avalanche. More specifically, a submarine avalanche. Off the coast of North America, there are a series of large channels that carry sediment out onto the abyssal plain on the ocean floor. The 1929 earthquake was large enough to set off an avalanche in one of these chasms. That avalanche carried material from the continental shelf to the deep ocean floor plain, and in the process released substantial energy.The energy from this landslide was enough to set off a major tsunami even though everything from it happened under water. The Earthquake itself didn’t cause the tsunami and it wasn’t even the right type of earthquake to trigger a tsunami. If one of these earthquakes happened today, no one would think to send off a tsunami warning until it actually hit land (and of course, there is no tsunami warning system in the Atlantic Ocean).So the question is how much of a risk does this pose to populated areas such as New York or Boston along the U.S. East Coast? New research presented at the meeting of the Seismological Society of America 2013 by Boston College researcher John Ebel suggests it’s entirely possible and very difficult to predict.In 2012, 280 kilometers (170 miles) off the coast of Boston, there was a series of small earthquakes. None of these were greater than magnitude 4.0, but these earthquakes along the continental shelf were the same type of setting as the quake in 1929. There were about 15 other small earthquakes along the continental shelf, in places from Newfoundland to Cape Cod as well.None of these earthquakes was large enough to trigger a similar landslide, but this process is poorly understood, and there’s likely a variety of conditions that could trigger a landslide. The earthquakes themselves are likely happening along old faults in the crust left over from when North America split away from Europe over 100 million years ago. Therefore, the earthquakes are rare, but since we have so little data on them, it’s also nearly impossible to estimate how likely they are in the future.These earthquakes may be rare, but if they happen occasionally, the entire East Coast of the U.S and the Atlantic coasts of Ireland, France, Spain, and Portugal could be at risk from similar phenomena. A large earthquake might be rare at one spot or on one fault, but given how many similar faults there are across the entire North Atlantic, these types of tsunamis could be much more common than anyone had ever thought.For comparison, the storm surge from Hurricane Sandy peaked at 11 feet above mean low tide; that’s just over 3 meters. The runup from the 1929 Newfoundland tsunami was 10 meters. Basically, everything in this image other than the bridge would be under water if the water came up that much.-JBBPhoto credit:Photo: Bebeto Matthews/APhttp://gizmodo.com/5958416/hurricane-sandy-the-craziest-before-and-after-shotsSeismic source info from 1929 earthquakehttp://www.bssaonline.org/content/77/6/1984.shorthttp://www.bssaonline.org/content/85/4/1003.shortPress report on new research:http://phys.org/news/2013-04-tsunami-east-coast.htmlSandy runup:http://originalweatherblog.blogspot.com/2012/10/sandy-proceeding-as-forecast.html -- source link

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