Tremors of mega Japan earthquake were also felt in space

Written By Unknown on Selasa, 12 Maret 2013 | 22.10

WASHINGTON: The massive earthquake that hit Japan on March 11, 2011 was also felt in space by ESA's hyper-sensitive GOCE satellite.

The massive earthquake sent ripples of sound - called infrasound - upwards through the atmosphere.

These sound waves caused changes in air density that were detected by ESA's GOCE gravity satellite as it crossed the wavefront.

Earthquakes not only create seismic waves that travel through Earth's interior, but large quakes also cause the surface of the planet to vibrate like a drum. This produces sound waves that travel upwards through the atmosphere.

The size of these waves changes from centimetres at the surface to kilometres in the thin atmosphere at altitudes of 200-300 km.

Only low-frequency sound - infrasound - reaches these heights. It causes vertical movements that expand and contract the atmosphere by accelerating air particles.

Since it was launched in 2009, GOCE has been mapping Earth's gravity with unrivalled precision, orbiting at the lowest altitude of any observation satellite.

But at less than 270 km up, it has to cope with air drag as it cuts through the remnants of the atmosphere.

The cleverly designed satellite carries an innovative ion engine that instantly compensates for any drag by generating carefully calculated thrusts. These measurements are provided by very precise accelerometers.

While the measurements ensure that GOCE remains ultra-stable in its low orbit to collect ultra-precise measurements of Earth's gravity, atmospheric density and vertical winds along its path can be inferred from the thruster and accelerometer data.

Exploiting GOCE data to the maximum, scientists from the Research Institute in Astrophysics and Planetology in France, the French space agency CNES, the Institute of Earth Physics of Paris and Delft University of Technology in the Netherlands, supported by ESA's Earth Observation Support to Science Element, have been studying past measurements.

When GOCE passed through these waves, its accelerometers sensed the vertical displacements of the surrounding atmosphere in a way similar to seismometers on the surface of Earth. Wave-like variations in air density were also observed.

Raphael Garcia from the Research Institute in Astrophysics and Planetology said, "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.

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


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