by Sambit Prasanajit Naik, Siva Sai Kumar Rajana, Sampad Kumar Panda, Chiranjeevi G. Vivek & Devanshu Ghildiyal

This study examines the Co-seismic Ionospheric Disturbances (CIDs) triggered by Mw 7.6 Cayman Islands earthquake along the transform fault setting in the Caribbean Sea on 8 February 2025 using the GNSS-based Total Electron Content (TEC) observations. The significance of characterizing the effects of this particular earthquake event through probing ionospheric perturbations lies in its occurrence under quiet solar and geomagnetic conditions. This provides unambiguous identification of ionospheric perturbations caused by lithospheric forcing from below, and valuable insights into solid Earth-ionosphere coupling mechanisms. The earthquake exhibited the two-stage rupture process, beginning with a slow initial sub-shear rupture phase followed by a rapid acceleration into the supershear regime. This rupture behavior facilitated the generation of strong ground motion and produced atmospheric acoustic-gravity waves (AGWs) that propagated upward and reached ionospheric altitudes. Notably, filtered TEC data exhibited distinct oscillations following the earthquake, which clearly showed the CIDs signatures with the amplitudes reaching up to 0.8 TECU. The filtered TEC values also exhibited the spatial asymmetry due to the atmospheric effects and the ambient geomagnetic field. Also, spectral analysis confirmed the dominant acoustic wave frequencies (2–4 mHz) and horizontal propagation velocities (~ 1.34 km/s) aligning with the theoretical acoustic wave speeds, which further confirmed the signatures of seismic origin ionospheric disturbances. These findings reinforce the role of CIDs as reliable indicators of seismic activity in transform plate boundary settings and highlight the potential use of GNSS networks for real-time earthquake monitoring. Source: https://doi.org/10.1007/s12145-026-02134-6