Analysis of GPS-based TEC and electron density by the DEMETER satellite before the Sumatra earthquake on 30 September 2009

Abstract

An analysis of ionospheric total electron content (TEC) variations obtained using Global Positioning System (GPS) measurements and electron density observations by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER)/ISL before the Sumatra earthquake (magnitude 7.6) on 30 September 2009 is presented. The data used are global TEC maps created in the IONEX format to estimate the spatial scale of ionospheric irregularities associated with this earthquake and DEMETER/ISL observations to analyse plasma parameter changes during earthquakes. This study for the first time integrates ground-based GPS receiver and space-based DEMETER/ISL observations to probe seismo-ionospheric anomalies before a large earthquake. The pre-seismic behaviour of the TEC was detected within a few days before the main event. The anomaly appeared as local TEC enhancement in the vicinity of the forthcoming earthquake epicentre. These structures were generated in the ionosphere at a similar local time at 1, 3 and 5 days prior to the main shock. The equatorial anomaly trough moved northwards (5°) on the earthquake day and 7.5° southwards the next day. The results demonstrate that both enhanced and reduced anomalies in the ionospheric electron density appeared before the Sumatra earthquake. The results from International GNSS Service (IGS) GPS data demonstrate that TEC variations can be used to detect seismo-ionospheric signatures.