December 5, 2011 – NASA Finds “Merging Tsunamis” Doubled Japan Destruction: NASA satellite data, on the major and destructive tsunami generated by the March 11, 2011 magnitude 9.0 Tohoku-Oki earthquake off Japan’s northeastern coast, were used to confirm the existence of long-hypothesized “merging tsunamis” capable of traveling long distances without losing power. The NASA/French Space Agency Jason-1 satellite (left) passed over the tsunami 7 hours and 30 minutes after the earthquake and was able to “see” a large wave resulting from merging tsunami jets. The NASA/European Jason-2 satellite (right) passed over the region 8 hours and 20 minutes after the earthquake and observed the normal tsunami wave.
Researchers have discovered the major tsunami generated by the March 11, 2011 Tohoku-Oki quake centered off northeastern Japan was a long-hypothesized “merging tsunami.” The tsunami doubled in intensity over rugged ocean ridges, amplifying its destructive power at landfall.
Data from NASA and European radar satellites captured at least two wave fronts that day. The fronts merged to form a single, double-high wave far out at sea. This wave was capable of traveling long distances without losing power. Ocean ridges and undersea mountain chains pushed the waves together 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. The data raise hope that scientists may be able to improve tsunami forecasts.
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. A NASA-French Space Agency satellite happened to be in the right place at the right time to capture the double wave and verify its existence.”
The Jason-1 satellite passed over the tsunami on March 11, as did two other satellites: Jason-2 and EnviSAT. All three satellites carry radar altimeters, which measure sea level changes to an accuracy of a few centimeters. Each satellite crossed the tsunami at a different location, measuring the wave fronts as they occurred.
This data will be used 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.
Scientists believe that 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 its destruction appear random. For that reason, hazard maps that try to predict where tsunamis will strike rely on sub-sea topography. Previously, these maps considered only topography near a particular shoreline. This suggests scientists may be able to create maps that take into account all undersea topography, even sub-sea ridges and mountains far from shore.
The satellite data was verified through model simulations based on independent data, including 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. This, in turn, could lead to more accurate coastal tsunami hazard maps to protect communities and critical infrastructure.
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