'Double tsunami' doubled Japan destruction

December 05, 2011

SAN FRANCISCO - Researchers have discovered that the destructive tsunami generated by the March 2011 Tōhoku earthquake was a long-hypothesized "merging tsunami" that doubled in intensity over rugged ocean ridges, amplifying its destructive power before reaching shore.

Satellites captured not just one wave front that day, but at least two, which merged to form a single double-high wave far out at sea - one capable of traveling long distances without losing its power. Ocean ridges and undersea mountain chains pushed the waves together, but only along certain directions from the tsunami's origin.

The discovery helps explain how tsunamis can cross ocean basins to cause massive destruction at some locations while leaving others unscathed, and raises hope that scientists may be able to improve tsunami forecasts.

At a news conference Monday at the American Geophysical Union meeting in San Francisco, Y. Tony Song, a research scientist at NASA's Jet Propulsion Laboratory (JPL); and C.K. Shum, professor and Distinguished University Scholar in the Division of Geodetic Science, School of Earth Sciences at Ohio State University, discussed the satellite data and simulations that enabled them to piece the story together.

"It was a one-in-ten-million chance that we were able to observe this double wave with satellites," said Song, the study's principal investigator. "Researchers have suspected for decades that such 'merging tsunamis' might have been responsible for the 1960 Chilean tsunami that killed many in Japan and Hawaii, but nobody had definitively observed a merging tsunami until now."

"It was like looking for a ghost," he continued. "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."

Shum agreed. "We were very lucky, not only in the timing of the satellite, but also to have access to such detailed GPS-observed ground motion data from Japan to initiate Tony's tsunami model, and to validate the model results using the satellite data. Now we can use what we learned to make better forecasts of tsunami danger in specific coastal regions anywhere in the world, depending on the location and the mechanism of an undersea quake."

The NASA/Centre National d'Etudes Spaciales Jason-1 satellite passed over the tsunami on March 11, as did two other satellites: the NASA/European Jason-2 and the European Space Agency's EnviSAT. All three carry a radar altimeter, which measures sea level changes to an accuracy of a few centimeters.

Each satellite crossed the tsunami at a different location. Jason-2 and EnviSAT measured wave heights of 20 cm (8 inches) and 30 cm (12 inches), respectively. But as Jason-1 passed over the undersea Mid-Pacific Mountains to the east, it captured a wave front measuring 70 cm (28 inches).

The researchers conjectured ridges and undersea mountain chains on the ocean floor deflected parts of the initial tsunami wave away from each other to form independent jets shooting off in different directions, each with its own wave front.

The sea floor topography nudges tsunami waves in varying directions and can make a tsunami's destruction appear random. For that reason, hazard maps that try to predict where tsunamis will strike rely on sub-sea topography. Previously, these maps only considered topography near a particular shoreline. This study suggests scientists may be able to create maps that take into account all undersea topography, even sub-sea ridges and mountains far from shore.

Song and his team were able to verify the satellite data through model simulations based on independent data, including the GPS data from Japan and buoy data from the National Oceanic and Atmospheric Administration's Deep-ocean Assessment and Reporting of Tsunamis program.

"Tools based on this research could help officials forecast the potential for tsunami jets to merge," said Song. "This, in turn, could lead to more accurate coastal tsunami hazard maps to protect communities and critical infrastructure."

Song and Shum's collaborators include Ichiro Fukumori, an oceanographer and supervisor in JPL's Ocean Circulation Group; and Yuchan Yi, a research scientist in the Division of Geodetic Science, School of Earth Sciences at Ohio State.
-end-
This research was supported by NASA.

Contact: Y. Tony Song via Alan Buis (818) 354-0474; alan.buis@jpl.nasa.gov
C.K. Shum, (614) 292-7118; ckshum@osu.edu

Written by Pam Frost Gorder, (Ohio State, 614) -292-9475; Gorder.1@osu.edu

Ohio State University

Related Tsunami Articles from Brightsurf:

Landslide along Alaskan fjord could trigger tsunami
Scientists noted that the slope on Barry Arm fjord on Prince William Sound in southeastern Alaska slid some 120 meters from 2010 to 2017, a slow-moving landslide caused by glacial melt that could trigger a devastating tsunami.

Scientists improve model of landslide-induced tsunami
MIPT researchers Leopold Lobkovsky and Raissa Mazova, and their young colleagues from Nizhny Novgorod State Technical University have created a model of landslide-induced tsunamis that accounts for the initial location of the landslide body.

Rethinking tsunami defense
Careful engineering of low, plant-covered hills along shorelines can mitigate tsunami risks with less disruption of coastal life and lower costs compared to seawalls.

'Tsunami' on a silicon chip: a world first for light waves
A collaboration between the University of Sydney Nano Institute and Singapore University of Technology and Design has for the first time manipulated a light wave, or photonic information, on a silicon chip that retains its overall 'shape'.

Tsunami signals to measure glacier calving in Greenland
Scientists have employed a new method utilizing tsunami signals to calculate the calving magnitude of an ocean-terminating glacier in northwestern Greenland, uncovering correlations between calving flux and environmental factors such as air temperature, ice speed, and ocean tides.

Salish seafloor mapping identifies earthquake and tsunami risks
The central Salish Sea of the Pacific Northwest is bounded by two active fault zones that could trigger rockfalls and slumps of sediment that might lead to tsunamis, according to a presentation at the 2019 SSA Annual Meeting.

Heading towards a tsunami of light
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation.

Paradigm shift needed for designing tsunami-resistant bridges
Researchers argue in a new study that a paradigm shift is needed for assessing bridges' tsunami risk.

How large can a tsunami be in the Caribbean?
The 2004 Indian Ocean tsunami has researchers reevaluating whether a magnitude 9.0 megathrust earthquake and resulting tsunami might also be a likely risk for the Caribbean region, seismologists reported at the SSA 2018 Annual Meeting.

Preparing for the 'silver tsunami'
Case Western Reserve University law professor suggests how to address nation's looming health-care and economic crisis caused by surging baby-boom population.

Read More: Tsunami News and Tsunami Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.