Spatial and temporal behaviour of Ionospheric VTEC and Atmospheric parameters before New Zealand earthquake on 13th November 2016 (M 7.8)

Abstract

In this paper, we present the results of the Ionospheric VTEC and atmospheric parameters such as Surface Latent Heat flux (SLHF), air temperature at 2 m from the surface (AT2m) and outgoing long-wave radiation (OLR) during New Zealand earthquake of M 7.8 on 13th Nov 2016 with a focal depth of 15.7 km. GPS data from 16 permanent IGS GPS stations from October 1 to November 19, 2016 are used for VTEC analysis. Global geomagnetic and solar parameters are also taken into account in the corresponding period. Both positive and negative anomalies in VTEC were observed using the Interquartile Sliding Moving Average method. Using the upper bound (UB) and lower bound (LB) of the VTEC time series, we observed a stronger enhancement of UB over the observed VTEC at the closer stations than at the far stations before New Zealand earthquake. We observed two VTEC anomalies 14 days and 2 days before this earthquake. By comparing the quiet days and the earthquake disturbed days, we observed significant deviations of the TEC on the earthquake disturbed days. The latitude variations of VTEC at each 30-min interval on November 13, 2016 clearly show the enhancement of the TEC signal just before the earthquake. TEC values appear to be normal between 00:00 and 04:30, peaking around 08:30 UT until the time of the earthquake (11:03 UT) in the New Zealand region. Atmospheric anomalies were calculated when the signal crossed the mean + 2*sigma; and with additional parameters such as the Excess Energy Flux Index (EEFI). SLHF parameters detected abnormal signal 33 and 18 days before the New Zealand earthquake. On October 18, 2016, the air temperature measured 286.25 °K at 2 m from the surface is 3.05 °K higher than the ten-year average and an “EEFI” of 2.18. The next day (October 19, 2016), the air temperature measured 2 m from the surface was 285.89 °K, while the ten-year mean air temperature at 2 m was 283.12 °K and the EEFI of 2.78. Two days after the second SLHF anomaly and four days before the earthquake (November 9, 2016), the anomalous fluctuations of AT2m for the current earthquake were observed for the second time. From the analysis of atmospheric parameters such as surface latent heat flux (SLHF), air temperature 2 m from the surface (AT2m) and outgoing long-wave radiation (OLR), it is observed that anomalous variations of these parameters were observed near the epicentral region before the New Zealand earthquake. VTEC together with atmospheric parameters (SLHF, AT2m and OLR) prove to be a promising tool for monitoring earthquake precursor signatures just before the New Zealand earthquake.