Ionospheric anomalies detected by GPS TEC measurements during two strong earthquakes in Indonesia

This paper reports the ionospheric anomalies observed during two strong earthquakes (M>6.0) which occurred in Southern Sumatra, Indonesia during 30 September–1 October 2009. The Global Ionospheric Maps (GIMs) of total electron content (TEC) provided by the International GNSS Service (IGS) network has been utilized. The solar and geomagnetic conditions were quiet during the two earthquakes. The upper and lower bound of inter-quartile range (IQR) were constructed to detect the abnormal earthquake-induced variations in TEC other than the diurnal and day-to-day pattern. Anomalous enhancements of TEC were detected 2–13 days before and 1–2 days after the earthquakes. The present results are in good agreement with previous observations reported by various researchers.