Seiches: Panama Canal & Norwegian Fjords

After the great tsunami of 2004, much-needed new attention was placed on the destructive force of large earthquakes, especially those capable of producing large tsunami events.  As a result of this increased awareness, many projects were begun to address the lack of tsunami warning systems around the world.

One project was the creation of a Caribbean-wide seismic network to identify seismic events which could generate a tsunami in this particularly vulnerable region.  My colleague Dan McNamara (USGS) led the multi-institutional project to build this network, where one of the stations was placed on an island found within the Panama Canal, station BCIP of the CU network.

Once the station had been in place for some time, and the data analyzed, a signal was identified in the long period (100 -200 seconds) that demanded further investigation.  As the title of this post suggests, it turned out that the source of this was standing water waves propagated through Lake Gatun, contributed by the ships passing through the canal.

A paper describing this phenomenon was written and can be found here.  This provides an example of how sloshing water, much like ocean tides, will readily couple with the surrounding land to create and propagate seismic waves through the earth itself, and how these may be successfully recorded and detected with a land-based seismometer.

Another seiche phenomenon was also recently identified resulting from the Tohoku event in March 2011 in Japan.  Namely, placid fjords in Norway started sloshing some 30 minutes after the earthquake in Japan, caused by the seismic waves of the event propagating around the globe.  A startling video of this can be found here, with an in-depth article found here.  I can’t understand what the people in the video are saying, but they must be very confused since conventional news of the quake most likely had not yet reached them.

So, two examples of seiches and how they relate to seismology: seiches produced by man-made sources and recorded as seismic waves on land, and seiches produced by a large earthquake very far away causing waves in still waters having no obvious local source.

Richard

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