Co-seismic ionospheric disturbances due to 2004 Sumatra-Andaman earthquake

The Coseismic Ionospheric Disturbances (CID) due to the 26th December 2004 earthquake of Mw 9.2, which occurred in the Sumatra-Andaman subduction zone, are analyzed using cGPS-aided Total Electron Content (TEC) measurements. For the CID analysis, data from nearby seven Sumatran GPS Array (SuGAr) and two International GNSS Stations (IGS) located to the south of the epicenter, at a distance of 500–1000km (near-field) and two IGS stations located to the north-west of the epicenter at a distance of 2000km (far-field) are considered. The CIDs with a propagation velocity of 595–694m/s arrived within 2–10min after the earthquake, depending upon the distance of a station from the epicentre. Variations in the CIDs can be prominently seen at the nearest cGPS Station SAMP immediately after the earthquake. NTUS, being the farthest station shows some small variations. The delay in the occurrence of variations at GPS sites can also be associated with rupture propagation. Because all the stations used in our analysis are located south of the epicenter and rupture of the earthquake propagated in the north, the trend of rupture propagation could not be analyzed clearly.