Application of the T2-Hotelling test for investigating ionospheric anomalies before large earthquakes

Abstract

In view of the frequent occurrence of large earthquakes, researchers have been always looking for ways to study and analyze these risky phenomena. Today, abnormal changes in ionosphere are taken as a means for this purpose. This article concentrates on the application of the T2-Hotelling test for detecting significant changes in the Total Electron Content (TEC) as an ionospheric parameter. The Global Ionosphere Maps (GIMs) are used for this purpose. The basic assumption is that TECs are normally distributed. This has been analyzed by using ten normality tests. Proposed method statistically analyzes the mean TEC changes using two samples of TECs. The first or the reference sample is 30 days long. The second or the target sample which is a moving one in time is 4 days long. The method is applied to the entire globe and therefore is a global method in nature. TECs associated with high solar and/or geomagnetic activity are not used when the reference sample is made. A sample of 12 earthquakes, occurred in 2010, with the moment magnitudes greater than 6 is used to analyze the efficiency of the proposed method. For 75% of the earthquakes in this study, proposed method confirms the seismo-ionospheric anomalies some of which have been already reported in the other researches. The rest of the studied quakes conform to the assertion that seismo-ionospheric anomalies might not be clearly visible even for some large earthquakes.