Seismo-ionospheric precursors of strong sequential earthquakes in Nepal region

Abstract

Global Navigation Satellite Systems record the total electron content via their receivers, and total electron content measurements have become popular with the requirement for capturing any ionospheric abnormalities prior to earthquake. Based on space weather conditions, the solar activity and geomagnetic activity indices are critical to monitor the total electron contents in the ionosphere. This study aimed to investigate the ionospheric variations induced by six sequential earthquakes in Nepal in 2015 with magnitude higher than 6.0, examine the total electron content data from Global Ionosphere Maps and Global Positioning Systems and analyze the contributing factors to the abnormal total electron content levels affected by space environment and geomagnetic activity status. We performed moving median analysis for 15 days to determine the pre- and post-earthquake abnormalities. With the static and dynamic time analysis, we concluded that there was likelihood for positive or negative anomalies, earthquake-induced ionospheric anomalies occurred on the previous day or up to six days earlier and even had potentiality for successive earthquakes.Furthermore, the data used in the analysis can be divided into two groups: Global Ionosphere Maps Total Electron Content and Global Positioning System Total Electron Content variations. LHAZ International Global Navigation Satellite System Service station from which we obtained these was close to the earthquakes’ epicenter. We studied three indices, such as geomagnetic storm index (K-planetary), geomagnetic activity index, and solar activity index, depending on space climate and discussed what factors can be influential in this disaster. Hence, we suggest that the earthquake may account for a typical variation in Global Ionosphere Maps Total Electron Content data as well as Global Positioning System Total Electron Content as solar activities and geomagnetic storms leading to abnormalities in the ionosphere.