Friday, April 8, 2011
The National Data Buoy Center (sorry, no Gurl Center) of NOAA describes the Deep-ocean Assessment and Reporting of Tsunamis (DART) program. Each DART gauge is designed to detect and report tsunamis, by looking at the pressure of the disturred column of ocean water.
Maps are available here to show the location of these sensors, such as the map below for the eastern side of Japan.
The image below shows the vauation in ocean height for the 24 hours and the 4 minutes surrounding the earthquake. Note the red onset of the higher frequency changes in ocean thickness on March 11 - that's the origin of the tsunami. It is soon followed by the maximum change of 1 meter, relatively small in the open ocean compared to the wave buildup when it approaches the shore.
For comparison sake, a normal period of four days showing diurnal tidal fluctuations with amplitudes of 0.5 meters looks like this: