How the 29 July 2025 M8.8 Kamchatka Earthquake Shook the Ionosphere Over Japan
Abstract
This study investigates the mid‐field (∼1,100–3,800 km) ionospheric response to the 29 July 2025 Kamchatka earthquake over Japan using multi‐instrument observations, raytracing, and numerical simulations. Total electron content (TEC) observations from GPS satellite G04 and Galileo satellite E10 show a maximum TEC perturbation of ∼0.5–0.85 TECU at ∼1,100 km, observed ∼17 min after the event. Travel‐time diagrams reveal two main groups of Co‐Seismic Ionospheric Disturbances (CSIDs) over Japan propagating at ∼3.0–3.5 km/s and ∼1.1–1.6 km/s, attributed to the fast, Rayleigh wave driven, seismo‐acoustic and slower direct acoustic/shock‐acoustic components, respectively. Beyond ∼2,100 km, these two groups become clearly separated, with the fast branch becoming more distinct over southwestern Japan, while the slow branch decelerates and dissipates. The vertical component of the seismic waveform indicates an average Rayleigh surface‐wave speed of 3.5 km/s, as measured by Japan's broadband seismograph network. Raytracing, treating the Rayleigh wave as a local acoustic source, substantiates the first CSID arrival observed in TEC data and confirms the dominant role of Rayleigh wave‐driven seismo‐acoustic coupling in the mid‐field region. Ionosonde observations from four Japanese stations reveal multi‐cusp (MC) structures in the ionograms, with onset times yielding a propagation speed of ∼3.6 km/s, closely matching the Rayleigh wave speed. Finally, numerical simulation using local seismic measurements reproduces the small‐scale (∼8 s/∼4–5 km) electron density perturbations detected by COSMIC‐2 in the lower F‐region (140–180 km) at ∼2,000 km from the source, confirming the role of the mainshock in triggering such perturbations.
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BibTeX
@article{barad2026july,
title = {{How the 29 July 2025 M8.8 Kamchatka Earthquake Shook the Ionosphere Over Japan}},
author = {R. Barad and E. Astafyeva and S. Sanchez and E. Kherani and I. Ouar and C. Maréchal},
journal = {Journal of Geophysical Research Space Physics},
year = {2026},
month = jul,
doi = {10.1029/2026ja035089},
url = {https://hal.science/hal-05778255v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - How the 29 July 2025 M8.8 Kamchatka Earthquake Shook the Ionosphere Over Japan
AU - R. Barad
AU - E. Astafyeva
AU - S. Sanchez
AU - E. Kherani
AU - I. Ouar
AU - C. Maréchal
PY - 2026
DA - 2026/07/20
JO - Journal of Geophysical Research Space Physics
DO - 10.1029/2026ja035089
UR - https://hal.science/hal-05778255v1
AB - This study investigates the mid‐field (∼1,100–3,800 km) ionospheric response to the 29 July 2025 Kamchatka earthquake over Japan using multi‐instrument observations, raytracing, and numerical simulations. Total electron content (TEC) observations from GPS satellite G04 and Galileo satellite E10 show a maximum TEC perturbation of ∼0.5–0.85 TECU at ∼1,100 km, observed ∼17 min after the event. Travel‐time diagrams reveal two main groups of Co‐Seismic Ionospheric Disturbances (CSIDs) over Japan propagating at ∼3.0–3.5 km/s and ∼1.1–1.6 km/s, attributed to the fast, Rayleigh wave driven, seismo‐acoustic and slower direct acoustic/shock‐acoustic components, respectively. Beyond ∼2,100 km, these two groups become clearly separated, with the fast branch becoming more distinct over southwestern Japan, while the slow branch decelerates and dissipates. The vertical component of the seismic waveform indicates an average Rayleigh surface‐wave speed of 3.5 km/s, as measured by Japan's broadband seismograph network. Raytracing, treating the Rayleigh wave as a local acoustic source, substantiates the first CSID arrival observed in TEC data and confirms the dominant role of Rayleigh wave‐driven seismo‐acoustic coupling in the mid‐field region. Ionosonde observations from four Japanese stations reveal multi‐cusp (MC) structures in the ionograms, with onset times yielding a propagation speed of ∼3.6 km/s, closely matching the Rayleigh wave speed. Finally, numerical simulation using local seismic measurements reproduces the small‐scale (∼8 s/∼4–5 km) electron density perturbations detected by COSMIC‐2 in the lower F‐region (140–180 km) at ∼2,000 km from the source, confirming the role of the mainshock in triggering such perturbations.
SN - 2169-9380
SN - 2169-9402
ER -