Fukushima quake 'heard at edge of space'

The great Tohoku earthquake that struck Japan in 2011, triggering a powerful tsunami that killed more than 16000 people, was so massive that its effects were even felt at the edge of space.
The Magnitude 9.0 quake on March 11, 2011, that triggered a tsunami and caused nuclear accidents at three reactors in the Fukushima Daiichi Nuclear Power Plant, sent a ripple of sound through the atmosphere that was picked up by the European Space Agency's Goce satellite, scientists say.
The ESA spacecraft encountered the signal as it passed over the Pacific some 30 minutes after the onset of the magnitude 9.0 quake, and then again 25 minutes later as it moved across Europe.

The satellite's super-sensitive instrumentation was able to detect the disturbance as it passed through the thin wisps of air still present 255 km above the Earth, the 'BBC News' reported.
It has long been considered that major quakes will generate very low-frequency acoustic waves, or infrasound - a type of deep rumble at frequencies below those discernible to the human ear. However, no spacecraft in orbit has had the capability to record them, until now.
"We've looked for this signal before with other satellites and haven't seen it, and I think that's because you need an incredibly fine instrument," said Dr Rune Floberghagen from ESA.

"Goce's accelerometers are about a hundred times more sensitive than any previous instrumentation and we detected the acoustic wave not once, but twice - passing through it over the Pacific and over Europe," the mission manager said.

Goce's prime purpose is to map very subtle differences in the pull of gravity across the surface of the Earth caused by the uneven distribution of mass within the planet.
These variations produce almost imperceptible changes in the velocity of the satellite as it flies overhead and which it records with those high-precision accelerometers.
However, this gravity signal is very weak, and that means Goce must fly incredibly low to sense it - so low, in fact, that it actually drags through the top of the atmosphere.

Today is the second anniversary of the quake and tsunami that claimed around 16,000 lives and destroyed property.