Statistical Behavior of Electron Density in the Ionosphere before 2016 Manipur Earthquake from GPS Observation Stations at North East India

The abnormalities in the ionosphere Total Electron Content (TEC) is linked to the deformation, stress accumulation and earthquake preparation processes in the earth’s crust and show anomaly prior to the occurrence of earthquakes. Detail analysis on TEC variation prior to 2016 Mw = 6.7 Imphal (India) earthquake is carried out using three Global Positioning System (GPS) Continuously Operating Reference Stations (CORS) installed each at Cherrapunjee (Meghalaya), Khanapara (Assam) and Madankamdev (Assam). TEC time series prior to earthquake indicates strong consistent anomalies at regular intervals on 5th, 9th, 25th, and 27th of December 2015. The time at which the TEC deviation is maximum and minimum as anomaly time is studied in detail to understanding TEC-earthquake epicenter distance relationship. It is observed that for positive anomaly, i.e., when TEC crosses upper limit defined by statistical method, at detected anomaly time, TEC concentration increases towards the epicenter. For negative anomaly when TEC crosses lower limit, TEC concentration decreases towards the epicenter. It is also observed that with distance the magnitude of TEC anomaly decreases and the maximum anomalous values are observed near to the earthquake epicenter. The study indicates need of a real time TEC monitoring system for effective precursor detection.