Investigation of ionospheric and atmospheric anomalies associated with three Mw >6.5 EQs in New Zealand

The dual-frequency Global Positioning System (GPS) provides insights to detect the ionospheric perturbations with Total Electron Content (TEC) variations induced by the Earthquakes (EQs) or geomagnetic storm effects. In this paper, we investigate abnormal ionospheric signatures before three large magnitudes (Mw 2 TECU during UT = 15-24 h (for New Zealand, UT = LT + 13) within 5-15 days before two EQs of Mw 7.8 and Mw 6.8. Whereas, a chain of positive and negative anomalies is generated by geomagnetic storm-EQ event (Mw 6.6) far beyond 5-15 days before and after the main shock due to active storm conditions (Kp 3; Dst < -50 nT). Furthermore, geomagnetic storm anomalies are dominant on Mw 6.6 EQ day to active storm conditions. To validate the ionospheric anomalies as possible seismic precursors, the atmospheric anomalies in relative humidity and OLR (outgoing longwave radiations) are also examined to exhibit the evolution of ionospheric anomalies from the lithosphere to ionosphere via the atmosphere. Moreover, EQ induced regular and collocated atmospheric anomalies over the epicenters of Mw 7.8 and Mw 6.8 and irregular atmospheric anomalies exist over the seismogenic zone of Mw 6.6 due to geomagnetic storm-EQ nature. The observed EQ anomalies will aid in the improvement of lithosphere atmosphere ionosphere coupling hypothesis during the seismic preparation phase over the epicenter of future EQ.