Fig. 4From: Monitoring of the ionosphere TEC variations during the 17th August 1999 Izmit earthquake using GPS dataVertical TEC observations, as observed from KANT, MERT and TUBI reference stations, during the period 13–22 August, 1999 (days 225#x2013;234). The star indicates the time of the earthquake (00.01 UT) and the circle indicates a low anomaly before the earthquake.Back to article page