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Preliminary research analyzed the Coseismic Ionospheric Disturbances (CIDs) of the strikeslip 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 ~300 km (F layer) by Chapman’s profile. We also conducted preseismic [ABSTRACT FROM AUTHOR]

The study of ionospheric disturbances associated with the two large strike-slip earthquakes in Indonesia was investigated, which are West Sumatra on 2 March 2016 (Mw = 7.8), and Palu on 28 September 2018 (Mw = 7.5). The anomalies were observed by measuring co-seismic ionospheric disturbances (CIDs) using the Global Navigation Satellite System (GNSS). The results show positive and negative CIDs polarization changes for the 2016 West Sumatra earthquake, depending on the position of the satellite line-of-sight, while the 2018 Palu earthquake shows negative changes only due to differences in co-seismic vertical crustal displacement. The 2016 West Sumatra earthquake caused uplift and subsidence, while the 2018 Palu earthquake was dominated by subsidence. TEC anomalies occurred about 10 to 15 min after the two earthquakes with amplitude of 2.9 TECU and 0.4 TECU, respectively. The TEC anomaly amplitude was also affected by the magnitude of the earthquake moment. The disturbance signal propagated with a velocity of ~1–1.72 km s−1 for the 2016 West Sumatra earthquake and ~0.97–1.08 km s−1 for the 2018 Palu mainshock earthquake, which are consistent with acoustic waves. The wave also caused an oscillation signal of ∼4 mHz, and their azimuthal asymmetry of propagation confirmed the phenomena in the Southern Hemisphere. The CID signal could be identified at a distance of around 400–1500 km from the epicenter in the southwestern direction. [ABSTRACT FROM AUTHOR]