Spatial distribution of ionospheric GPS-TEC and NmF2 anomalies associated with the Chi-Chi earthquake

Recently, scientists find an apparent reduction in GPS-TEC within 1-5 days prior to M26.0 earthquakes in Taiwan. However, those studies did not cross examine simultaneous data in other places to confirm seismo-ionospheric anomalies observed. In this paper, we retrieved GPS-TEC routinely published in the global ionosphere maps (GIM). Simultaneous data of ionosonde and GPS-TEC in various locations such as Taiwan and Japan are examined to check whether the anomaly observed in Taiwan during the 1999 Chi-Chi earthquake (M-7.6) is the local or global effect. The result shows that the anomalies in Taiwan on 3 days before the Chi-Chi earthquake are local phenomena. It means that the ionospheric disturbed area was local around Taiwan, and did not spread to Tokyo. We conclude that the disturbed area is less than about 2200 km in radius.