Changes in total electron content associated with earthquakes (M > 5) observed from GPS station, Varanasi, India

Abstract

The total electron content (TEC) derived from the global positioning system (GPS) at Varanasi (latitude 25.3° N, longitude 82.99° E), India has been measured during 2007 and 2010. We have chosen nine earthquakes (M > 5) that occurred within 2000 km of Varanasi during 2007 and 2010 to study the changes in TEC associated with these earthquakes. A monthly median (MM) of the TEC and associated inter quartile range (IQR), upper bound (UB) and lower bound (LB) are utilized as a reference for identifying abnormal signals during all nine earthquakes. The results show anomalous reductions and enhancements in the TEC. These pre-earthquake ionospheric anomalies appear within 5 days prior to earthquakes. A possible mechanism responsible for ionospheric anomalies associated with earthquakes is discussed.