Photograph from Kyodo/Reuters
Rescue workers, appearing small against the rubble in red and orange uniforms, search through the remains of Noda-mura village, in the Iwate Prefecture in northern Japan, on March 14, 2011.
To cause the tsunami that wreaked devastation here and along the east coast of Japan, the earthquake three days earlier in the northwest Pacific Ocean had to have produced, at minimum, energy that was equivalent to 475 megatons of TNT, according to the estimates that scientists at the U.S. Geological Surveyhave developed.
That's equivalent to the energy content of 326 million barrels of crude oil, close to the amount the world consumes in four days.
The energy in an earthquake is one of the few forces of nature that is closely measured by scientific instruments. Seismograph readings enable scientists to estimate the energy that an earthquake radiates through the earth, shaking buildings near and far. Even so, the instruments do not capture the whole picture, for example, the energy dissipated as heat through friction.
With a magnitude of 9.0, last year's earthquake was the largest to rock Japan and among the largest ever measured.
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