Observations of the Japanese Tsunami

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Natural disasters like the recent earthquake in Japan have impacts far beyond the local devastation.  Our societies are connected by personal and economic ties, which make even far away events seem close at hand.  However, powerful earthquakes can, quite literally, be felt around the world.  

Although he is 17,000 km away from Japan, intrepid graduate student Pete is living in a house a few meters above sea level on the coast of Chile.  When the tsunami warnings went out, Pete and I immediately began exchanging email.  Thankfully, Pete's distance gave him ample time to get to safety and enough time to attempt to sample the wave.  Pete has been using low cost pressure sensors to measure the tide in Melimoyu Bay and the outflow of the nearby river, and he made sure that two of the sensors were set in the Bay prior to the arrival of the tsunami waves.  

While the full saga will hopefully appear on the Patagonia blog (it involves spending the night on a hill in the forest), I'd like to share Pete's initial scientific findings.  The image below is the record of water depth at one location during the passage of the tsunami.  

The gray line is the water level we would expect from the tide alone.  Some interesting things to note:

  1. The wave arrived at about 3AM on Sunday morning, approximately 24 hours after the earthquake.  This means that the wave traveled about 700 kph (440 mph).  This is only 60 mph slower than the cruising speed of an Airbus A340, although the Airbus would probably need to refuel and would have a tough time landing at the airstrip in Melimoyu.
  2. The wave consisted of a series of wave packets.  The number, shape, and frequency of the waves gives information on the path that the wave took to get to Melimoyu.  Wave speed of a tsunami depends on the wave length and the depth of the ocean.  Longer waves travel faster and the waves travel faster in deep water.
  3. The waves persist for several hours, and Pete reported that the Bay was still doing funny things 12 hours later.  Some of the length is due to dispersion as the wave traveled across the Pacific, but there is likely a component due to the wave "echoing" in the islands and fjords.  

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This page contains a single entry by Andy Pershing published on March 14, 2011 10:32 AM.

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