http://www.ouramazingplanet.com/japan-earthquake-rattled-upper-atmosphere-1842/

“Scientists detected a disc-shaped rise in electron density in the ionosphere about seven minutes after the earthquake. Concentric waves of fluctuating electron density then flowed out in the ionosphere from this disk at speeds of about 450 to 500 mph (720 to 800 kph). All in all, this disruption was about three times greater than the next largest one ever seen, which came after the 2004 magnitude 9.3 Sumatra earthquake.

The ripples that flowed from the initial disc-shaped disturbance in the ionosphere appear to be linked to the tsunami, a connection that has the potential to save lives. “This signature in space that we can see with GPS could provide early warning that a tsunami is coming,” researcher Jann-Yenq “Tiger” Liu, an atmospheric scientist at Taiwan’s National Central University, told OurAmazingPlanet.”