Satellite ‘Hears’ Earthquake From Space
Japan's Tohoku earthquake in 2011 was felt by the GOCE satellite.
CREDIT: ESA/IRAP/CNES/TU Delft/HTG/Planetary Visions
A satellite that was originally designed to monitor gravity variations across the Earth’s surface also recently functioned as the world's first space-based earthquake detector, a new study shows.
And that could have consequences that go far beyond our home planet, since other geologically active planets — such as Venus — could be studied from orbit.
In a recent paper published in Geophysical Research Letters, scientists describe how the ESA's GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite detected sound waves from the 2011 earthquake off the coast of Japan.
Quakes that shake the ground also produce sound waves that travel vertically through the atmosphere. They're too low frequency to be heard by human ears, but GOCE, though designed to study minute changes in the Earth's gravity caused by variations in the distribution of mass throughout the planet, was in a perfect position to pick up on those waves – not too high up or too low, and at just the right latitude.
Astrophysicist Raphael Garcia of the University of Tolouse explained: "The upper atmosphere is moving on its own dynamics. At high latitudes, the dynamic is strongly influenced by magnetic storms."
Thus, the acoustic signal from tiny changes in air density caused by the earthquake's rumblings would have been lost among the swirling upper atmosphere if the satellite was parked at high latitudes.
GOCE was also at just the right altitude, 167 miles (270 km) up, where the signals aren't too muffled (as they are lower down) or distorted (higher altitudes result in loss of the highest frequencies). And if it were even higher, outside the Earth's atmosphere entirely, there wouldn't have been any air for the acoustic signals to pass through.
While science has had the ability to track earthquakes from space for some time, previous methods have relied on radar. This is the first time an earthquake has been "heard" from space.
The technique might make it possible to study quakes on other planets. "On Venus, you cannot deploy your seismometer on the ground, because the surface temperature is very high," Garcia said. "So maybe studying these waves generated by these quakes may be the only way to infer what is going on."