Total electron content variations related to seismo-ionospheric precursors and seismic/tsunami waves triggered by the 29 July 2025 Mw 8.8 Kamchatka Earthquake

The total electron content (TEC) of the global ionosphere map (GIM) is used to study seismo-ionospheric precursors (SIPs) of the 29 July 2025 Mw 8.8 Kamchatka earthquake. Statistical analyses show that SIPs of GIM TEC significantly frequently decrease specifically over the epicenter area on day 21-26 and 1 before the earthquake.  The distance between northern and southern crests of equatorial ionization anomaly in GIM TEC as well as downward ion velocities measured by advanced ionospheric probe (AIP) onboard FORMOSAT-5 (F5) satellite are used to estimate electric fields associated with the observed SIPs. Results show that the seismo-electric fields related the two SIPs estimated by the GIM TEC and F5/AIP ion velocity are about 1 mV/m westward.  Meanwhile, TEC derived by more than 1,400 ground-based GNSS receiving stations in Japan and Taiwan is employed to examine the spatiotemporal evolution of seismic- and tsunami-traveling ionospheric disturbances (STIDs and TTIDs). A normalized process applied to GNSS TEC clearly shows STIDs and TTIDs traveling with the horizontal speeds of 3.6 km/s and 273.2-215.4 m/s, respectively.  The estimated TTID source is located within about 90 km of the center of the main slip area.