17:15 〜 19:15
[SSS13-P01] Re-examination of TEC anomalies in the ionosphere before large earthquakes
キーワード：TEC、大地震の予測
Since the 2011 Mw 9.0 Tohoku earthquake, the possibility of short-term earthquake forecasting using total electron content (TEC) anomalies observed via Global Navigation Satellite System (GNSS) monitoring has been proposed (Heki, 2011). Heki (2011) reported that positive TEC anomalies appeared 10 to 80 minutes before the origin times of the Tohoku and other large earthquakes. However, subsequent studies (e.g., Eisenbeis and Occhipinti, 2021) argued that these anomalies were artifacts of data analysis methods rather than actual pre-seismic signals. In this study, we re-examine the existence of "pre-seismic TEC anomalies" before several large earthquakes, including the Tohoku earthquake, by comprehensively analyzing data from multiple GNSS station-satellite pairs. To mitigate station-specific noise, we employ a spatial stacking approach based on latitude and longitude and remove the moving average. In the case of the Tohoku earthquake, we find that the pre-seismic signals identified by Heki (2011) first appear in the northeast (Hokkaido) region and later in the southwest (Kyushu) region. This pattern contradicts the expected outward spread of a pre-seismic TEC anomaly from the epicentral region. Our analysis, which includes Akaike's Information Criterion (AIC) applied to stacked vertical TEC (vTEC) time series data and animations of vTEC fluctuations over Japan, suggests that the observed anomalies were unrelated to the Tohoku earthquake. Instead, they are likely associated with large-scale traveling ionospheric disturbances (LSTID). Further, our analysis of non-earthquake days reveals similar propagation phenomena, reinforcing the likelihood that these anomalies are not seismically induced. These findings suggest that previously reported pre-seismic TEC anomalies for other large earthquakes may also be explained by LSTID rather than earthquake-related processes. Our results contribute to resolving the ongoing debate on the existence of pre-seismic TEC signals and their potential role in short-term earthquake forecasting.