Multi-station GNSS analysis of co-seismic crustal deformation and a critical re-assessment of candidate seismo-ionospheric precursors for the 2004 Sumatra–Andaman earthquake
Acta Geodaetica et Geophysica, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Basım Tarihi: 2026
- Doi Numarası: 10.1007/s40328-026-00524-2
- Dergi Adı: Acta Geodaetica et Geophysica
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex, Geobase, Academic Search Ultimate (EBSCO), Natural Science Collection (ProQuest), Earth, Atmospheric, & Aquatic Science Collection (ProQuest)
- Anahtar Kelimeler: 2004 Sumatra–Andaman earthquake, Kinematic PPP, LAIC, Precursor non-confirmation, Regional GNSS network, VTEC anomaly
- Yıldız Teknik Üniversitesi Adresli: Evet
Özet
This study jointly analyses the crustal deformation and the ionospheric behaviour associated with the 2004 Sumatra–Andaman earthquake (Mw 9.1–9.3) using a regional GNSS network of six continuously operating stations (SAMP, BAKO, NTUS, IISC, DGAR and PIMO). Kinematic Precise Point Positioning processed with CSRS-PPP is combined with PCA-based common-mode-error filtering, Z-score and CUSUM change-point testing, and geomagnetic screening using the Kp and Dst indices. The geodetic analysis resolves a dominant co-seismic horizontal displacement of ~26 ± 2 cm in the west-southwest direction at SAMP, 306 km from the epicentre, decaying to millimetre level at the far-field sites (BAKO ~0.4 cm, DGAR ~0.8 cm, at or below the noise floor of the technique); these values agree with published regional tectonic models and validate the processing pipeline. The ionospheric analysis, based on the geometry-free L4 combination of all 102 station-days of dual-frequency observations between 15 and 31 December 2004, does not support the pre-seismic vertical-TEC enhancement that has been reported for 21 December 2004 in earlier work. On that date the daily VTEC anomaly is negative at five of the six stations and + 0.2 TECU at the sixth, the network-mean robust z-score is − 0.86, and no station exceeds the + 2.5σ detection threshold; the largest positive network-wide departures of the analysis window fall on 22 and 24 December and on the mainshock day itself, none of them reaching that threshold. The candidate precursor is therefore not confirmed. The result illustrates how strongly reported seismo-ionospheric precursors depend on the reference baseline, the bias handling and the elevation screening adopted, and it underlines the need for multi-station spatial-coherence testing and rigorous geomagnetic screening before any candidate anomaly is interpreted within the Lithosphere–Atmosphere–Ionosphere Coupling framework.