Satellite recorded Japan quake

(File photo, AP)
(File photo, AP)
Washington - A European Space Agency satellite circling Earth was able to detect the massive 2011 earthquake that ravaged Japan, killing nearly 16 000 people and causing massive destruction, a new study said on Sunday.

"The atmospheric infrasounds following the great Tohoku earthquake... induced variations of air density and vertical acceleration of the Goce platform," said a report published in the journal Geophysical Research Letters.

The Gravity Ocean Circulation Explorer (Goce) is the European Space Agency super-sensitive satellite that acts like an orbital seismologist.

Scientists argue that earthquakes not only create seismic waves that travel through Earth's interior, but large tremors also cause the surface of the planet to vibrate like a drum. This produces sound waves that travel upward through the atmosphere.

Goce is designed to capture and register these signals.

Shock waves

According to the report, the magnitude 9.0 tremor on 11 March 2011 sent shock waves through the atmosphere that was picked up by the satellite.

"These signals were detected at two positions along the Goce orbit corresponding to a crossing and a doubling of the infrasonic wave front created by seismic surface waves," the study said.

It noted that perturbations up to 11% of air density and a vertical acceleration of air waves were observed following the quake.

"These perturbations were due to acoustic waves creating vertical velocities up to 130 metres per second," the report pointed out.

The satellite first recorded the signal as it passed over the Pacific Ocean about 30 minutes after the quake and then again 25 minutes later as it moved across Europe.

"Seismologists are particularly excited by this discovery because they were virtually the only Earth scientists without a space-based instrument directly comparable to those deployed on the ground," said Raphael Garcia from the Research Institute in Astrophysics and Planetology in France.

"With this new tool, they can start to look up into space to understand what is going on under their feet."
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