Ionospheric Irregularities Signature Correlation on ROT Variation for Earthquake Detection and Epicenter Estimation: Case Study of Tohoku (2011) & Turkey-Syria (2023) Earthquakes

Natural Phenomena such as earthquakes, volcanic eruptions, solar storms cause variation of Total Electron Contents (TEC), and Global Navigation Satellite System (GNSS) has been used to monitor these ionospheric variations. Especially, Rate of TEC Index (ROTI) which can be derived from geometry-free combination of signals and S_4, sigma_phi indices that denotes scintillation of signal have been used to detect ionospheric irregularities. However, ROTI shows different calculation result with respect to different sampling rate and averaging time interval, and S_4,sigma_phi indices are unsuitable for small and fast-moving ionospheric irregularities. Thus, in this paper, we suggest a method of detecting ionospheric irregularities due to earthquakes using ROT and have studied the method of estimating epicenter of the earthquakes. ROT fluctuations and observed at different times depending on the location of the satellite and the reference stations. By estimating this time difference using Inter-Station Cross Correlation, it is possible to estimate the speed of ionospheric irregularities. The location of the epicenter can be estimated using the geometric relationship between the reference stations and the Ionospheric Pierce Point (IPP) where ROT fluctuation had occurred. Algorithm of epicenter estimation was analyzed based on actual data, and we had proposed the fields where these methods are applicable.