This collection of images illustrates the damage from the March 2011 Japanese Earthquake. Image Credit/BBC
Three Earth observing satellites are helping scientists explain the enormous destructive force of the tsunami summoned by the Tohoku-Oki Earthquake centered off northeast Japan in March.
The magnitude 9 quake on March 11 and the events that followed killed more than 15,000 people, left several thousand more missing, while destroying or damaging an estimated 600,000 buildings, according to the website Earthquake-Report.com. Multiple meltdowns were recorded at the Fukushima Nuclear Power Plant, and the estimates for the destruction range to over $200 billion.
Scientists from NASA and Ohio State University, funded by NASA, have used the observations from the radar altimeters on three satellites to detect a merging of smaller tsunamis into a larger single destructive wall of water that pounded Japan’s Pacific coastline. Long hypothesized as a possibility, the merging of multiple tsunamis doubled the damages, according to Y. Tony Song of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and C.K. Shum, an Ohio State University researcher.
The two men presented their findings this week at the annual meeting of the American Geophysical Union in San Francisco,Calif.
According to their work and previous research, undersea ridges and other rugged subsurface formations caused at least two wave fronts spotted by the satellites to merge into a double high wave far out to sea but headed for landfall in northeastern Japan.
The discovery helps explain how tsunamis can cross ocean basins to cause massive destruction at some locations, while leaving others unscathed, according to a NASA statement on the presentation. The data raise hope that scientists may be able to improve tsunami forecasts.
The NASA-Centre National d’Etudes Spaciales Jason-1 satellite passed over the tsunami on March 11. So did two other spacecraft, the NASA-European Jason-2 and the European Space Agency’s EnviSAT.
All three spacecraft carry radar altimeters, which measure sea level changes to an accuracy of a few centimeters, NASA reported. Each satellite crossed the tsunami at a different location, measuring the wave fronts as they occurred.
The scientists used simulations of the observations to piece together the story of destruction.
“It was a one in 10 million chance that we were able to observe this double wave with satellites,” Song told a media briefing at the AGU meeting, according to the NASA statement.
“Researchers have suspected for decades that such ‘merging tsunamis’ might have been responsible for the 1960 Chilean tsunami that killed about 200 people in Japan and Hawaii, but nobody had definitively observed a merging tsunami until now,” Song said. “It was like looking for a ghost. A NASA-French Space Agency satellite altimeter happened to be in the right place at the right time to capture the double wave and verify its existence.”