Traveling Coseismic Ionospheric Disturbance
observed with a dense GPS array

Heki, K. and J.-S. Ping, Earth, Planet. Sci. Lett., 236, 845-855, 2005.

Seismic waves propagating through the ionosphere were observed after the 2003 Tokachi-Oki Earthquake, Hokkaido (Mw=8.0). Their apparent velocity (~1 km/sec), period (~300 sec), time lag (~10 minutes after the earthquake), and directivity (southward beam) suggest that they are acoustic waves induced by the sudden uplift of the sea surface.