Abstract
Data analysis method (CRA, hereafter) to correlate multiple TEC anomaly signals has detected pre-seismic anomalies before the 2011 Tohoku-Oki earthquake (Iwata & Umeno 2016), the 2016 Kumamoto earthquake (Iwata & Umeno 2017) and the 2016 Tainan earthquake (Goto et al. 2019). However, a critical argument said that those anomalies detected by CRA would not be pre-seismic anomalies published by Journal of Geophysical Research-Space Physics (126), 2021 (JGR-SP (126), hereafter). In this paper, we would point out its incorrect use of statistical anomalies in evaluating CRA as the following points: CRA is shown to increase the signal-to-noise ratio (SNR) to amplify pre-seismic TEC’s small anomaly signals with synchronizing and correlating multiple GNSS receivers’ data. We proved again that pre-seismic anomalies certainly exist before the 2011 Tohoku-Oki earthquake and the 2016 Kumamoto earthquake with additional data analysis. In particular, as a temporal anomaly, deceleration at propagation velocities of medium-scale traveling ionospheric disturbances (MSTID, hereafter) before the 2016 Kumamoto earthquake captured by CRA (Iwata & Umeno 2017) is elucidated as pre-seismic anomalies. Furthermore, we proposed a physical model to predict that 35 m/s change at MSTID propagation velocities estimated by TEC’s CRA requires 0.58 × 10-3 V/m electric field in the F Layer ionosphere. Contrary to the claim with the incorrect use of statistical anomalies in JGR-SP (126), TEC’s correlation anomalies detected by CRA (Iwata & Umeno 2016 and Iwata & Umeno 2017) clearly provided supporting evidence that physical pre-seismic anomalies really exist.
Highlights
CorRelation Analysis (CRA, hereafter) is a general method to extract signal from complicated noise in diverse kinds of signal processing
For the issue on distinction between ionospheric anomaly and medium-scale traveling disturbances (MSTIDs), the reference [11] argues that the 65 - 168 m/s MSTID propagation velocity range firstly reported in I & U17 as total electron content (TEC) preseismic anomaly is not abnormally low as compared to the statistics on the propagation velocities reported in the past [20] and Ikuta et al concluded that TEC anomaly detected for the 2016 earthquake day reported in I & U17 is not a preseismic one
We have shown that contrary to the claim by [11] which is shown to have multiple fatal errors in the judgement of capability of detecting TEC pre-seismic anomalies with the incorrect use of statistical anomaly, TEC’s correlation anomalies detected by I & U16 and I & U17 clearly provided supporting evidence that physical pre-seismic anomalies really exist before the two large earthquakes, respectively
Summary
CorRelation Analysis (CRA, hereafter) is a general method to extract signal from complicated noise in diverse kinds of signal processing. C(T) of GPS 17 shows a strong anomaly (C(T) higher than 100) while C(T) of GPS28 shows no anomaly (C(T) less than 10) even at the same GNSS stations (gais-wanc of Taiwan) at the same time period (17:00-20:00 UTC) on the earthquake day (Feb. 5., 2016) This means whether TEC pre-seismic correlation anomalies can be detected or not are dependent on the SIP (sub-ionospheric) track of the satellite. In this respect, the reference [11] is incorrect because they calculated based on the statistics of C(T) with all kinds of GNSS satellites used in their analysis. We argue that the reference [11] has several fatal errors with incorrect use of statistical anomalies for evaluating CRA
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