Seiches

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Seiches

Post #1 by GrannyGrottbags » Wed Aug 21, 2013 9:03 am

Long, slow waves are known as seiches.
They can occur in any landlocked body of water, such as a lake and are often by strong winds.
In some cases they can be created by earthquakes thousands of miles away.
Norwegian fjords are particularly sensitive to the natural occurrence because of their great depths.
Back in 1950, the Assam earthquake triggered waves in 29 fjords in Norway and in English reservoirs.
However, the latest finding is the first known recording of Norwegian seiches caused by an earthquake for over half a century.

How 2011 Japanese earthquake created freak 5ft waves that terrified locals on the other side of the world - in Norway
The waves, known as seiches, can occur in any landlocked body of water
They are sometimes triggered by earthquakes thousands of miles away
This is the first known recording of Norwegian seiches caused by an earthquake for over half a century
When 5ft waves were suddenly seen rising from the Aurland-Flåm fjord in Norway, locals were terrified.

They described the event, which occurred in 2011, as ‘like a maelstrom’ and as if ‘the sea was boiling.’
Some captured the waves on their mobile phones, watching the water ebb and flow to great heights for several hours at a time.
Now, a new study has revealed that the mystery waves were in fact made by the huge magnitude-9.0 earthquake that devastated Japan in 2011.
The freak waves, known as seiches, can occur in any landlocked body of water, such as a lake, for a variety of reasons.
Often they are caused by strong winds, but in some cases they can also be created by earthquakes thousands of miles away.
Experts initially thought the waves in 2011 were caused by an underwater landslide.
But the explanation didn’t account for reports of coastal flooding at the same time in other fjords in Norway.
Fjords pointing northeast toward Japan, in five towns, started moving half an hour after the Japan earthquake and continued to do so for almost three hours.
‘I realised there must be a connection with the big earthquake in Japan,’ Stein Bondevik, a geologist at Sogn og Fjordane University College in Sogndal, told LiveScience.
‘I was so excited I couldn't sleep that night thinking about it.’
Bondevik and his team used videos taken by eye witnesses and built a computer model to test their theory by timing the ebb and flow of the oscillations.He found that these seiches were triggered from horizontal S waves caused by the 2011 Tohoku earthquake.

An S-wave is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving.
Mr Bondevik claims that in fjords pointed northeast, the S-waves from the Japan earthquake moved the ground back and forth by 0.4 inches.
According to researchers, Norwegian fjords are particularly sensitive to the natural occurrence because of their great depths.
Back in 1950, the Assam earthquake triggered waves in 29 fjords in Norway and in English reservoirs.
However, the latest finding is the first known recording of Norwegian seiches caused by an earthquake for over half a century.
Read more: http://www.dailymail.co.uk/sciencetech/ ... z2caYWqduz
http://www.dailymail.co.uk/sciencetech/ ... quake.html

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