Abstract The detection of earthquake (EQ) related ionospheric anomalies using the Global Navigation Satellite System (GNSS) has emerged as a convincing approach and new field in the search for seismic precursors. Total Electron Content (TEC) from International GNSS services (IGS) network may help to distinguish seismo ionospheric anomalies from geomagnetic storm induced anomalies. In this paper, spatial and temporal TEC anomalies are investigated in 1 sec resolution data from GNSS stations around the epicenter of the August 19, 2018, Fiji EQ (Mw 8.2). Moreover, median and standard deviation based anomaly detection techniques are implemented on TEC and the variations are quantified on the basis of z-test at α = 0.05 significance level. We find evidence of significant ionospheric anomalies of low intensity within 5-10 days before and 5 days after the main shock by estimating TEC from four GNSS stations within the EQ preparation period. On the other hand, a significant ionospheric anomaly of high intensity occurred after the main shock more than 5 days after the EQ, which is associated with an intense geomagnetic storm (Dst =-150 nT and Kp ≥ 7). More analysis reveals that EQ induced TEC anomalies are significant during Local Time (LT) = 08:00-16:00 (for Fiji, LT= UT+12) and similarly the storm (Dst =-150 nT and Kp ≥ 7) induced TEC anomaly prevails in all GNSS stations during LT= 08:00-18:00. The TEC intensity of the storm anomaly is more substantial in all four GNSS stations compared to the EQ induced TEC anomaly. All these anomalies before and after the main shock during the EQ preparation period are advantageous towards differentiating seismic versus storm anomalies. Furthermore, this analysis aids in the developing hypothesis of lithosphere ionosphere coupling through TEC monitoring.

中文翻译：

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可能与 GNSS TEC 检测到的 2018 年 M 8.2 斐济地震有关的地震电离层异常

摘要 使用全球导航卫星系统 (GNSS) 检测地震 (EQ) 相关的电离层异常已成为寻找地震前兆的令人信服的方法和新领域。来自国际 GNSS 服务 (IGS) 网络的总电子含量 (TEC) 可能有助于区分地震电离层异常与地磁暴引发的异常。在本文中，在 2018 年 8 月 19 日斐济 EQ (Mw 8.2) 震中附近的 GNSS 站的 1 秒分辨率数据中研究了空间和时间 TEC 异常。此外，在 TEC 上实施了基于中值和标准差的异常检测技术，并在 α = 0.05 显着性水平上基于 z 检验对变化进行量化。我们通过在 EQ 准备期间估计来自四个 GNSS 台站的 TEC，发现了主震前 5-10 天和主震后 5 天存在明显低强度电离层异常的证据。另一方面，在 EQ 后 5 天多的主震后发生了显着的高强度电离层异常，这与强烈的地磁暴（Dst =-150 nT 和 Kp ≥ 7）有关。更多分析表明，EQ 引起的 TEC 异常在当地时间 (LT) = 08:00-16:00（斐济，LT= UT+12）和类似的风暴（Dst =-150 nT 和 Kp ≥ 7）引起的在 LT= 08:00-18:00 期间，所有 GNSS 站都存在 TEC 异常。与 EQ 引起的 TEC 异常相比，风暴异常的 TEC 强度在所有四个 GNSS 站中都更为显着。EQ 准备期间主震前后的所有这些异常有利于区分地震异常与风暴异常。此外，该分析有助于通过 TEC 监测发展岩石层电离层耦合的假设。