Chen said that a tsunami could be triggered by the movement of the Earth's plates during an earthquake. The earthquake and tsunami waves will be transport along the Earth's surface and vertical displacements due to these waves in ground and sea surfaces will produce acoustic waves propagating upward to the atmosphere and ionosphere.

Once the acoustic waves arrive ionosphere, they could travel horizontally away from the epicenter with velocity four times faster than tsunami, Chen revealed.

These are the so-called seismo-traveling ionospheric disturbances (STID). The STID has inference not only to the GPS navigation, but also to the satellite communications.

It was the very first time for scientists to observe such clearest and strongest tsunami-induced STID seen during 11 March 2011 Japan Tohoku by dense ground-based GPS receiver networks.

The team used high dense GPS receivers along Japan and Taiwan and detected the signal of STID after the earthquake. The concentric structures of ionospheric disturbances induced by the tsunami waves were found.

From the propagation times of ionospheric disturbances and tsunami waves, it is found that the ionospheric disturbances arrived Taiwan around 1.5 hours after the earthquake onset while the tsunami waves arrived Taiwan around 4 hours after the earthquake onset, which means there is a 2.5-hour of leading time for warning.

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