A note on the correlation of seismo-ionospheric perturbations with ground motions as deduced from F-net seismic observations

. The purpose of this paper is to try to find any correlation between the ionospheric perturbation as detected by subionospheric VLF/LF propagation and ground motions as detected by wideband seismic observations (so-called F-net). Two huge earthquakes are chosen for our analysis; (1) Niigata-chuetsu-oki earthquake on July 16, 2007 and (2) Iwate-nairiku-nambu earthquake on June 13, 2008. The AW(acoustic wave, period=1-10 min) and AGW(atmospheric gravity wave, period=10-100 min) components in the ground motions are compared with the ionospheric perturbation. It is found that the ground motions in the AGW and AW ranges are enhanced as compared with the backgrounds when the lower ionosphere is perturbed, which might be a possible source of ionospheric perturbation. Though the number of events is only two, this correlation may lend a support to the atmospheric oscillation hypothesis of the lithosphere-ionosphere coupling due to some precursory ground effect. by means of the direct observations of Doppler-Journal