Ionospheric perturbations linked to a very powerful seismic event

Ionospheric anomalies in association with the powerful Hachinohe earthquake (M=8.3) are derived using foF2 (F2 layer O-mode critical frequency) records from worldwide ionospheric stations. The results show that meaningful decreases in foF2 are identified only at several ionospheric stations near the epicenter, indicating that the anomalies extend to about 1500 km from the epicenter. These anomalies are observed a couple of days before and/or after the main shock and the duration of each anomaly is one-day. The anomalies occur predominantly during daytime.