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

Abstract

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 ∼300 km (F layer) by Chapman’s profile. We also conducted preseismic studies of ionospheric anomalies before the earthquake as an additional analysis.

3D Traveling Ionospheric Disturbances During the 2022 Hunga Tonga–Hunga Ha’apai Eruption Using GNSS TEC

“…(2018) and Muafiry and Heki (2020) as well as Cahyadi et al. (2020, 2022a) have previously used the 3D tomography test with the checkerboard test model.…”

Directivity of Coseismic Ionospheric Disturbances Propagation Following the 2016 West Sumatra Earthquake Using Three-Dimensional Tomography GNSS-TEC

“…Each voxel is limited to latitude, longitude, and altitude, and the electron density anomaly is assumed to be homogeneous. Observation of absolute STEC anomaly (∆STECi) with each beam path is estimated as the number of electron density anomaly products per unit length and voxel penetration length [10]:…”

“…n is the total number of voxels, a ij and x j are the beam path length and electron density of the j th voxels, and e i is the observed and approximate errors. Equation ( 1) can be expressed in matrix form as follows when the total number of line-of-sights (LOS) is m [10]:…”

“…The refinement of the CID spatial distribution analysis was conducted by Cahyadi et al [8], which observed the 2020 Turkey earthquake. These observations provide an overview of the spatial distribution found in detail from an altitude of 100-600 km.…”

“…Rahayu et al [9] also comprehensively observed the earthquake, but the data used cannot analyze spatial distribution. Cahyadi et al [10] succeed to analyze CID and the directivity of propagation as 3D tomography in the 2018 Palu earthquake. The epicenter of the earthquake was in the equatorial region, where an anomaly was found moving to the south.…”