How Credible Are Earthquake Predictions Based on TEC Variations?

摘要

The possible relation between pre-earthquake processes and ionospheric fluctuations is widely investigated and debated. Here, we conduct a numerical experiment to examine two studies that reported preseismic anomalies in the ionospheric total electron content (TEC) and argue for the significance of their respective analyses based on statistical evaluations. The first study is that by Liu et al. (2018, https://doi. org/10.3319/tao.2018.03.11.01), who statistically investigated the relationship between 62 M ≥ 6 earthquakes occurred in China over an 18-year period and the TEC, which was deduced from the Global Ionospheric Map. According to this study, the TEC showed anomalies with specific polarities at certain days and times that preceded the earthquakes. Earthquake alarms they defined based on these anomalies showed a good performance. We conduct this same analysis using random synthetic earthquakes and obtain results that closely match those by Liu et al. (2018, https://doi.org/10.3319/tao.2018.03.11.01), thus indicating that the good performance of the Liu et al. (2018, https://doi.org/10.3319/tao.2018.03.11.01) alarm is an artifact. The second study is that by Le et al. (2011, https://doi.org/10.1029/2010ja015781), who classified the TEC time series into anomalous and non-anomalous days based on the TEC perturbation. They found that the anomalous day rate increased as the nucleation time of the earthquakes was approached, especially for larger and shallower earthquakes. We conduct the same analysis using random synthetic earthquakes. The anomalous day rate that is comparable to their result occurs in ~40% of the 1,000 random trials, thereby suggesting that their result may also be an artifact.