AsianScientist (Mar. 13, 2013) – Satellites map changes in the Earth’s surface caused by earthquakes but in the first ever recorded study, an orbiting satellite has sensed sound waves from a quake directly in space.
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. Soundwaves produced from the quake travel upwards through the atmosphere, with sizes that start at centimeters at the Earth’s surface, to kilometers at high altitudes.
In a study published in the journal Geophysical Research Letters, researchers found that the 9.0 magnitude 2011 Tohoku earthquake that triggered a massive tsunami sent ripples of low-frequency sound – called infrasound – upwards through the atmosphere.
These soundwaves were detected by the European Space Agency’s GOCE gravity satellite as it crossed the wavefront. Orbiting at less than 270 km above the Earth, the GOCE satellite has to cope with air drag as it cuts through the remnants of the atmosphere. It compensates for any drag using its ion engine that generates carefully calculated thrusts. These measurements are provided by very precise accelerometers.
When the GOCE satellite passed through the soundwaves, 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.
“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 lead author Raphael Garcia from the Research Institute in Astrophysics and Planetology. “With this new tool they can start to look up into space to understand what is going on under their feet.”
On Monday, Japan remembered the 20,000 people who died in the earthquake and tsunami that devastated its northeastern coast two years ago. Approximately 150,000 people remain displaced from their homes.
The article can be found at: Garcia RF et al. (2013) GOCE: the first seismometer in orbit around the Earth.
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Source: ESA; Photo: ESA/IRAP/CNES/TU Delft/HTG/Planetary Visions.
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