The TEC Enhancement Before Seismic Events Is an Artifact

Eisenbeis, J.; Occhipinti, G.

doi:10.1029/2020ja028733

Cited by 14 publications

(8 citation statements)

References 45 publications

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“…GNSS TEC observations have since been employed to characterize the three‐dimensional distribution of the increase in ionospheric electron density preceding the 2010 Chilean earthquakes (He & Heki, 2016) and the 2015 Illapel earthquake (He & Heki, 2018), as well as the TEC increase preceding global M7‐8 earthquakes (He & Heki, 2017). However, it has been suggested that the observed variations in Heki (2011) may be due to space weather (Utada & Shimizu, 2014), and that the method adopted in Heki (2011) and He and Heki (2016, 2017, 2018) may have produced artifacts that were influenced by post‐earthquake ionospheric disturbances (Eisenbeis & Occhipinti, 2021; Kamogawa & Kakinami, 2013; Masci et al., 2015). A number of recent studies have claimed to overcome these artifacts by not including post‐earthquake data in their respective analyses (Goto et al., 2019; Heki & Enomoto, 2013, 2015; Iwata & Umeno, 2016).…”

Section: Introductionmentioning

confidence: 99%

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How Credible Are Earthquake Predictions Based on TEC Variations?

Ikuta

Oba

2022

JGR Space Physics

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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.

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Section: Introductionmentioning

confidence: 99%

“…disturbances (Eisenbeis & Occhipinti, 2021;Kamogawa & Kakinami, 2013;Masci et al, 2015). A number of recent studies have claimed to overcome these artifacts by not including post-earthquake data in their respective analyses (Goto et al, 2019;Heki & Enomoto, 2013Iwata & Umeno, 2016).…”

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confidence: 99%

How Credible Are Earthquake Predictions Based on TEC Variations?

Ikuta

Oba

2022

JGR Space Physics

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“…He claimed to have found anomalous enhancements in TEC starting ∼40 min before large earthquakes. Several researchers pointed out the possibility that he was looking at TEC change due to solar‐related sources, rather than earthquakes (Utada & Shimizu, 2014), and others pointed out that changes in TEC could be a methodological artifact (Kamogawa & Kakinami, 2013; Masci et al., 2015, and later Eisenbeis & Occhipinti, 2021). Then, Heki and co‐authors improved the method and introduced an objective index and threshold for anomaly detection and then claimed that it is unlikely that the anomalies occurred by chance before earthquakes based on the low frequency of solar‐related anomalies detected by their threshold (Heki & Enomoto, 2015), although which is still been criticized that the frequency was underestimated (Ikuta et al., 2020; Tozzi et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

Reanalysis of the Ionospheric Total Electron Content Anomalies Around the 2011 Tohoku‐Oki and 2016 Kumamoto Earthquakes: Lack of a Clear Precursor of Large Earthquakes

et al. 2021

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We investigate the veracity of the reports by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036) and Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921), both of which claimed that the observed perturbations in Global Navigation Satellite System (GNSS)‐based ionospheric total electron content (TEC) could serve as a "precursor" of large earthquakes based on correlation analysis. Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036 defined a spatial correlation of residuals between the observed and predicted TEC time series. They reported that the correlation value is significantly larger before large earthquakes than those observed during non‐earthquake periods. Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921, who applied the same method to other large earthquake, claimed that the preseismic ionospheric disturbances can be distinguished from other non‐earthquake phenomena based on the small percentage of area where the correlation value exceeds the criterion. They also claimed that the low propagation velocity of the correlation peaks is also a preseismic characteristic. Here we tested their claims using a larger data set. As a result, these three characteristics they claimed to have captured as evidence of earthquake precursors are not significant being frequently observed during normal (nonearthquake) days. In addition to that, the criteria of Iwata and Umeno (2017, https://doi.org/10.1002/2017ja023921 cannot be applied to the large earthquake discussed by Iwata and Umeno (2016, https://doi.org/10.1002/2016ja023036, and vice versa. Therefore, we can find no basis for claiming that they detected precursors to the earthquakes. The calculation procedure of the correlation function shows that the value is more of an indicator that amplifies small variations synchronized between nearby stations, like medium‐scale traveling ionospheric disturbances rather than earthquake precursors.

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“…The existence of pre-seismic TEC anomalies before large earthquakes has been debated until today (Heki 2011 [4], Kamogawa & Kakinami 2013 [5], Heki & Enomoto 2013 [6], Masci et al 2015 [7], Kelley et al 2017 [8], Muafiry & Heki 2020 [9], Eisenbeis & Occipinti 2021 [10]). Such debate for a decade is caused by lacking of conclusive physical models to explain pre-seismic TEC anomalies.…”

Section: Introductionmentioning

confidence: 99%