Water Quality Sonde Detects Tsunami Signal Over 4,000 Miles Away

The waters were still frigid off the pier at Dockton Park, in the Quartermaster Harbor, just outside of Seattle. This is to be expected in March, so far north in Washington State, and the team for the King County Department of Natural Resources & Parks were well prepared in their cold-weather gear. Tsunami-Topo-Map-Washington.jpg

They were heading out to retrieve a fixed 6600EDS V2 sonde, which had been previously deployed to monitor depth, among other parameters. This retrieval was standard procedure; extract the data and inspect the condition of the sonde – a typical day on the job.

What wasn’t typical, however, was the nature of the data that had been recorded. Where they usually saw a consistent rise and fall of the tides there was now a curious period where the record had become “sloshed.” It was as if, for a full three days of tide action, some new force had been introduced that changed the readings. To understand how this happened, we will have to dive back into recent history.

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On March 11, 2011, Japan was rocked by the most powerful earthquake ever recorded off its coast, and the fifth most powerful earthquake recorded world-wide. This earthquake was so intense that it moved the main island of Japan eight feet to the east, and shifted the Earth on its axis by estimates of between four inches to 25 centimeters.

Worse still for the Japanese people, the quake generated destructive tsunami waves reaching heights of 133 feet which made it as far as six miles inland in some cases. Aside from the tragic loss of life and destruction of property the earthquake and tsunami also contributed to the now world-infamous Fukushima Daiichi nuclear disaster.

From its epicenter, some 232 miles from Tokyo, the tsunami traveled west to crash into the island. To the east however, the quake energy was free to travel across the Pacific Ocean relatively undaunted. As it traveled greater distances it continued to lose energy until it eventually drifted into the west coast of the Americas. By the time it reached the U.S. a good deal of its power had been dispersed, so much so that a casual observer out for a stroll may not have perceived any change. Tsunami-Dockton-YSI-photo.jpg

However, because the King County team was already using an integrated monitoring system, they were in the perfect position to catch this event. At the pier in Dockton Park the fixed 6600EDS V2 sonde’s pressure transducer was exactly what was needed to catch the subtle change in conditions caused by the event over 4,000 miles away.

The sonde itself is mounted to the underwater dock piling so that water level changes with the local tides in Dockton Park can be measured and quantified. As mentioned earlier, this requires trained professionals to regularly retrieve the sonde from its fixed position so that data can be extracted and so the sonde can be inspected for the next deployment.

Following the earthquake event, after the energy had traveled across the Pacific, the water depth in Quartermaster harbor rose by about two to five centimeters. The wave energy generated by the initial tsunami and aftershocks were measured for a full three days.

Tsunami-YSI-Water-Quality-Sonde.jpgBecause the King County team were already sampling for depth at an average of 15-minute intervals they found beautifully correlated data that shows the tsunami effect. In the graph above you can see the nature of the tides preceding the event. In the bracketed area they have highlighted the “sloshing” effect created by the earthquake energy. Following the event, after all of the energy had dissipated, readings returned back to their expected values. When providing this data to YSI, Marine Biologist for King County, Kimberle Stark simply said, “Pretty cool!”

Of course, the sonde is just part of the equation, and much credit must be given to the professionals over at King County. They have taken the time to understand their equipment and have taken the appropriate steps to regularly maintain and condition their sonde between deployments. Due to their diligence and proper use of their equipment they were able to capture some really interesting data generated half-way around the globe.

 

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Data from the 6600EDS V2 sonde showing water level.  The tsunami effect can be clearly seen as a distortion of the readings, or 'sloshing'.  Data courtesy of the King County Department of Natural Resources & Parks.

Figure 1 - Quartermaster Harbor, Washington Monitored by the King County Department of Natural Resources & Parks
Figure 2 - Illustration depicting the epicenter of the 2011 earthquake off the coast of Japan, and those sites effected.
Figure 3 - An integrated weather station at Dockton Park in Quartermaster Harbor. Credit: Bob Kruger
Figure 4 - 6600EDS V2 legacy sonde at the Seattle Aquarium. Credit: Shawn Larson
To learn more about what the team over at King County, Washington is up to, visit their website at: green.kingcounty.gov/marine  

 

 

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