Coseismic Multiple Cusp Signatures in VIPIR Ionograms from SKiKP-Excited Infrasound following the 2025 MW 8.8 Kamchatka Earthquake

Following the MW 8.8 Kamchatka earthquake on 29 July 2025, we observed coseismic Multiple Cusp Signatures (MCS) in successive 1-min ionograms recorded by the VIPIR ionosonde near Koror, Palau (PL407). We attribute these signatures to plasma displacements driven by three seismogenic infrasonic waves generated by teleseismic SKiKP phases. Doppler measurements reveal downward plasma displacements associated with each infrasonic wave. We further propose that the Palau barrier reef lagoon may serve as an efficient infrasonic wave generator, enabling MCS formation despite strong seismic attenuation over the ~4350 km epicentral distance.