How Earthquakes Make Spacewaves

Nov. 12 -- The 7.9 Denali earthquake that ripped across Alaska last year may have to be reclassified as a "spacequake." That monster temblor sent out seismic waves that rippled through the Earth's atmosphere and, for the first time, were detected far above the ground by scientists.

Using the latest in satellite technology, scientists in Europe and the United States captured a clear signal as pressure waves generated by the earthquake moved through the ionosphere, a region of charged particles in the Earth's very thin upper atmosphere.

The finding may lead to better techniques for monitoring earthquakes, particularly quakes on the ocean floor where there are no seismographs. But even if that never comes to pass, the finding is intriguing because it proves that earthquakes can even impact the air around us.

Disrupted Signals

The research, sponsored chiefly by the European Space Agency, builds upon work in the 1960s that showed that when a fault moves, the displacement sends out an acoustic signal, or radio wave, that moves up through the atmosphere. It's sort of like the sound wave generated by the vibration of a loud speaker in a sound system.

It was an interesting finding, but a bit frustrating.

"It was not really easy to do any interesting work on it," says geophysicist Juliette Artru, because no one was quite how to grapple with an event that takes place more than 50 miles above the ground.

Artru was working on her doctorate at the Institute de Physique du Globe in Paris when she hit on a challenging idea.

The ionosphere can be a pain in the neck sometimes because of its well known tendency to interfere with radio waves, including signals from Global Positioning System satellites. Thus that region of the Earth's atmosphere might be particularly sensitive to outside interference, like a sound wave from the ground.