Ionospheric Disturbances Induced by the 29 July 2025 Kuril–Kamchatka Earthquake: Multi‐Instrument Observations and Analysis

Abstract In this work, we investigate co‐seismic ionospheric disturbances (CSIDs) generated by the M8.8 earthquake of 29 July 2025 east of Petropavlovsk‐Kamchatsky, Russia. By combining Ionosonde, global navigation satellite system slant TEC (sTEC) measurements, seismic waveforms, and time‐distance (TTD) analysis, we track earthquake‐induced perturbations across five azimuthal sectors extending from the western Pacific to the American west coast. We detected CSIDs with velocity 2.95–3.23 km/s linked to Rayleigh surface waves and associated acoustic waves, with Rayleigh‐wave velocities of 3.46–3.87 km/s. Multiple‐cusp signatures are identified on ionograms, indicative of vertical electron density perturbations associated with Rayleigh waves. Tracking nodes of these MCS perturbations across consecutive profiles yield apparent vertical velocities of 411–880 m/s, providing approximate constraints on upward propagation. sTEC‐derived CSID velocities show good agreement with MCS‐inferred speeds, ranging from 2.42 to 3.91 km/s, while delays of 8–18 min relative to Rayleigh‐wave arrivals reflect acoustic coupling and ionospheric propagation. This study highlights the anisotropic propagation of earthquake‐driven ionospheric disturbances and underscores the value of a multi‐instrument approach in resolving both horizontal and vertical dynamics of CSIDs.