Three-Dimensional Tomography of Coseismic Ionospheric Disturbances Following the 2018 Palu Earthquake and Tsunami from GNSS Measurements

Preliminary research analyzed the Coseismic Ionospheric Disturbances (CIDs) of the strike-slip earthquake that occurred in Palu on September 28, 2018 (Mw = 7.5) and the materialization of a TEC anomaly with an amplitude of 0.4 TECU approximately 10-15 min later. The TEC anomaly amplitude is also affected by the magnitude of the earthquake moment; therefore, 3D analysis is needed to determine the spatial distribution of the ionospheric disturbances. This research aims to analyze the ionospheric disturbance of an earthquake in 3D using the Global Navigation Satellite System (GNSS) from the Geospatial Information Agency (BIG) or InaCORS stations spread over Sulawesi, Kalimantan, West Nusa Tenggara, East Nusa Tenggara, Bali, and Java with a 30 s sampling interval using GLONASS and GPS satellites. The checkerboard accuracy test was also carried out to evaluate the reliability of the 3D tomography model. The result showed that CIDs occur to the north and south of the epicenter around the equator, following the N-S Asymmetry theory. Furthermore, the tomography results indicate the presence of dominant and positive anomaly values at an altitude of 300-500 km. This follows the characteristics of variations in the ionosphere layer, where an altitude of 300-500 km is included in the F layer. The dominant anomaly at an altitude of 300 km is in accordance with the theory of the ionosphere's height, which experiences maximum ionization at an altitude of similar to 300 km (F layer) by Chapman's profile. We also conducted preseismic studies of ionospheric anomalies before the earthquake as an additional analysis.