Manifestation of earthquake preparation zone in the ionosphere before 2021 Sonitpur, Assam earthquake revealed by GPS-TEC data

Abstract

Global Positioning System (GPS) Continuously Operating Reference Station (CORS) data analysis shows that the ionosphere's electron density variability is linked to the deformation and stress accumulation in the Earth's crust. Anomalies in ionosphere total electron content (TEC) variability before 2021 M6.4 Sonitpur, Assam earthquake were detected using L1 and L2 GPS frequencies that showed three distinct abnormalities on April 3, 9, 10, 2021. Pearson's correlation coefficient (r) of TEC decreases in the CORS that lies away from the earthquake epicenter, indicating the possibilities of a positive relationship between TEC variability and earthquake epicenter. TEC concentration also decreases towards the epicenter within the earthquake preparation zone (EPZ). It is also observed that the Pearson's correlation coefficient (r) of TEC decreases linearly near the EPZ. The study demonstrates the possibilities of determining the TEC anomalous zone in the ionosphere that coincides with the EPZ in the crustal rocks. The research indicated the possibilities of magnitude estimation of an impending earthquake based on the TEC anomalous zone in the ionosphere using closely spaced dense CORS network data.