Radar shows that ocean currents off the coast of Hokkaido, Japan, changed abruptly during the March tsunami. Larger arrows show faster current flows. Blue and red dots are radar stations. (Credit: Belinda Lipa)

“It could be really useful in areas such as southeast Asia where there are huge areas of shallow continental shelf,” reports John Largier, an oceanographer at the University of California, Davis and author of a new paper published in the journal Remote Sensing.

Largier and collaborators from Hokkaido and Kyoto universities in Japan and San Francisco State University used data from radar sites at Bodega Bay, Trinidad, Calif., and two sites in Hokkaido, Japan, to look for the tsunami offshore.

Rather than picking up the actual tsunami wave—which is small in height while out at sea—the radar senses changes in currents as the wave passes.

The researchers could see the tsunami once it entered shallower coastal waters over the continental shelf. As the waves enter shallower water, they slow down, increase in height, and decrease in wavelength until finally hitting the coast.

The continental shelf off the California coast is quite narrow, and approaches to the coast are already well-monitored by pressure gauges, Largier says. But radar detection could be useful, for example, on the East Coast or in Southeast Asia, where there are wide expanses of shallow seas.

The work was supported by the National Science Foundation, the California Coastal Conservancy, the Sonoma County Water Agency, and the National Oceanographic and Atmospheric Administration.

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