Pre-earthquake Atmospheric and Ionospheric Anomalies before Taiwan Earthquakes (M 6.1 and M 6.4) on February (4th and 6th), 2018

Abstract

Satellite measurements are becoming popular among the scientific community to identify earthquake precursors since its spatial coverage is more and round the clock measurements are possible. In this paper, we analyzed Total Electron Content (TEC), Outgoing Longwave Radiation (OLR), Sea Level Pressure (SLP), Surface Latent Heat flux (SLHF) and Sea Surface Temperature(SST) to identify any abnormal anomalies before Taiwan earthquakes which occurred on 4th February 2018 (M = 6.1, depth = 12 km) and 6th February 2018 (M = 6.4, depth = 17 km). The GPS data of International GNSS Service(IGS) stations (TWTF and CKSV) which operated 90 and 200 km away from the epicenter of the earthquake on 6th February 2018 respectively, were used for calculation of VTEC. The locations of these stations are within the preparatory zone of these earthquakes. The global parameters such as Dst, Kp, and IMF are also analyzed for the corresponding period of VTEC. We noticed the raise of temporal variations of 5–8 TECU before few days of the present earthquakes. The VTEC and other parameters such as SLP, SST, SLHF, and OLR were analyzed using the “Sliding Interquartile range method” during the period of 09th Jan to 10th Feb 2018 (33 days) to identify the abnormal signal due to these earthquakes. Strong positive anomalies occurred one day before the earthquake of 4th February and 1st, 3rd and 5th day before the Taiwan earthquake of 6th February 2018 with strong anomalous nature with an absolute amplitude of 5–8 TECU.The Cross wavelet analysis between Kp and TEC is carried out to study the impact of global geomagnetic activity on TEC during the seismic event and we found a negligible influence of global geomagnetic activity. The good raise of SLP on the day of the earthquake on 6th February 2018 have been noticed with the raise of 300 mb, the SLHF anomalies are observed at the interface of the earth’s surface and atmosphere. Moreover, anomalous variations in air temperature and OLR were observed 2 days before the occurrence of the earthquake on 6th February 2018. Well co-ordinated scrutiny of various parameters such as TEC, SLHF, and OLR indicates that they can be used as promising precursors to the impending devastating earthquakes with reasonable accuracy.