Fig. 2.

(a) and (b) Travel-time diagrams of slant TEC time series filtered from 1 to 10 mHz for satellites 15 and 21–22 respectively, as observed by the GPS receivers of GEONET. The plain grey line has a 3.5 km/s slope, the dashed grey line 1 km/s, the magenta plain line 225 m/s and the dashed magenta line of the panel (b) 171 m/s. Those four lines all have an origin at the seismic origin time and should be shifted by the time of arrival of the wave at the maximum of ionization to correspond to real travel-time diagrams. (c) Sample of filtered TEC maps showing the gravity wave emitted by the rupture. Dashed circles are centered on the epicenter location and drawn every 500 km. A movie containing the whole sequence of ionospheric anomalies observed after the earthquake (from 5:30 UT to 9:00 UT) can be viewed at the following link: http://ganymede.ipgp.fr/~tohoku/ (movie1).