Earthquakes associated subionospheric VLF anomalies recorded at two low latitude stations in the South Pacific region

The JJI VLF (22.2 kHz) transmitter signal received at two low-latitude stations, one in Port Vila (geog. coord., 17.73°S, 168.33°E), Vanuatu and other Suva (18.14°S, 178.44°E), Fiji, was analyzed for any changes due to 16 Earthquakes (EQs) with magnitudes 5.5 7.7, during 2018 (JJI-Vanuatu path, 6.8 Mm) 2007 (JJI-Suva 7.5 Mm). amplitude analysis included terminator time (TT), average daytime nighttime variation, fluctuation, mother Morlet wavelet methods. Out of EQs only eleven have shown subionospheric including the decrease about 2–8 h on EQ day, unusual shifts TT up 5–9 min, 1–1.5 dB 1–5 dB, respectively, mainshock day EQs. dA(t) < 0 condition observed 4–5 days before which stabilized after 3–4 from day. A non-normalized normalized trend below -2σ (standard deviation) mark found an increase NF dispersion above +2σ seismic activity found. Mother associated showed a strong enhanced presence short frequency (∼0.05–0.10 mHz) wave-like signatures, few prior, EQ, as compared normal days.