J. Earth Syst. Sci. (2021) 130:149 Ó Indian Academy of Sciences https://doi.org/10.1007/s12040-021-01650-x (0123456789().,-volV)(0123456789().,-volV) Ionospheric and atmospheric perturbations due to two major earthquakes (M [ 7.0) 1, 2 2 SANJAY KUMAR *, PRASHANT KUMAR SINGH ,ROHTASH KUMAR , 1 1 AKSINGH and R P SINGH 1Atmospheric Research Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221 005, India. 2Department of Geo-Physics, Banaras Hindu University, Varanasi 221 005, India. *Corresponding author. e-mail: [email protected] MS received 16 October 2020; revised 10 March 2021; accepted 25 March 2021 The perturbation produced in the atmosphere/ionosphere associated with earthquake precursors during seismic activity of two major earthquakes which occurred on (1) 24 June 2019 in Indonesia (M = 7.3) and (2) on 19 August 2018 at Ndoi, Fiji (M = 8.2), are studied. Based on statistical analysis of total electron content (TEC) data, the presence of ionospheric perturbations 5 days before and after the main shock are found, which depends on the distance as well as direction of observation point from the epicentre. In general, ionospheric perturbations after the EQ at all the stations are found larger than that before the EQ. Probable mechanisms behind these perturbations associated with EQ are also being discussed. The ionospheric perturbations are observed at stations which are at larger distances from the epicentre, but not observed over other stations in different directions which are comparatively closer to the epicentre. These results suggest that seismic induced ionospheric anomaly is not isotropic in nature. Ozone data from three satellites: AIRS, OMI, and TOMS-like and MERRA-2 model are also analyzed 5 days before the EQ day and compared to the monthly average level. A strong link between anomalous variation in ionospheric TEC and atmospheric ozone data prior to both the EQs is noticed. Keywords. GPS; ionosphere; earthquake; seismo-ionosphere precursor; ozone. 1. Introduction preparatory stage, anomalous changes occur in the lithosphere and as a result, seismic electric signal Earthquake, a natural sudden and relatively (SES), radioactive elements, and leakage of carrier unpredicted phenomenon causes huge destruction gases: CH4,CO2, He, and H2 (Pulinets 2004; to human life, material properties, eco system Pulinets and Ouzounov 2011) are produced which environment and regional structural changes. move upward and produce ionization in the near Therefore, to reduce huge losses it is essential to Earth atmosphere (Sorokin and Hayakawa 2013), develop earthquake prediction technique both at acoustic pressure waves (Astafyeva et al. 2013), short- and long-time scales. Long-time scale pre- release of positive holes (Freund 2013), under- diction seems to be difBcult due to very weak signal ground emission of aerosols (Pulinets et al. 2000), produced during the early preparatory stage of electromagnetic radiations (Parrot 1994), etc. earthquake. Therefore, presently emphasis is to These may cause perturbations in atmospheric develop techniques for short-time predictions electric Beld, generation of atmospheric gravity (Hayakawa and Hobara 2010). In the earthquake waves, ionospheric electron density distribution, 149 Page 2 of 15 J. Earth Syst. Sci. (2021) 130:149 temperature, composition change and ionospheric of 24 June 2019 and (ii) Ndoi, Fiji Earthquake of 19 peak parameters of F2-layer NmF2, foF2, TEC of August 2018. TEC and ozone data for the period of the ionosphere. Measurements of these perturba- 5 days before and after the two earthquakes are tions may provide information about earthquake analyzed to understand possible implication of and its precursor signals. earthquakes on atmosphere/ionosphere. In the recent past, numerous ground- and satel- lite-based measurements have been used to study 2. Data and analysis pre- and post-seismic anomalies in different layers of the ionosphere (Liu et al. 2001; Sharma et al. The main shock of the Indonesian earthquake of 2010; Maurya et al. 2013; Aggarwal 2015; Sunil magnitude 7.3 started at 02:53:39 UT on 24 June et al. 2015). The pre-seismic induced electric Beld 2019. The epicentre was located at 292 km NW of depending upon its polarity with respect to existing Saunmalaki, Indonesia (lat. 6.408°S, long. electric Bled may produce enhancement or 129.16°E). Figure 1 shows map location of the depression in TEC of the ionosphere (Sharma et al. earthquake epicentre which is marked by symbol * 2010; Priyadarshi et al. 2011a;Liet al. 2015; Kelley with the red colour. The circle of earthquake et al. 2017). The E 9 B instability seems to be the preparation zone is drawn by blue colour and GPS most likely physical mechanism responsible for the stations lying inside the preparation zone are seismo-ionospheric anomaly formation (Namgal- denoted by symbol + (with blue colour for NDOI adze et al. 2007). Using ground-based measure- earthquake and green colour for Indonesian earth- ments, Liu et al. (2001) and Li et al. (2011) quake). Blue circle of the earthquake preparation reported simultaneous and significant decrease of zone has been drawn by considering epicentre as a the ionospheric electron density, foF2 and TEC centre and radius ‘R’ calculated using the relation which were observed 1–4 days before the Chi-Chi, q =100.439M, where M is the magnitude of earth- Rei-Li and Chia-Yi earthquakes. Using GPS data, quake (Dobrovolsky et al. 1979). Similar exercise Ouzounov et al. (2011) have constructed global has been done for the second earthquake which ionospheric map (GIM) over the Japanese region occurred at Ndoi, Fiji on 19 August 2018. Tables 1 and showed strong enhancement in electron den- and 2 describe brief details of the earthquakes and sity 3 days before the earthquake. Enhancement in location of stations from where data are used in GPS-TEC data just 40 min before the Tohoku this study. earthquake has been reported by Heki (2011). The GPS observation data in RINEX FORMAT Recently, case study and statistical analysis have are downloaded from the website (http://ftp:// been made to observe the pre-seismic anomalies in cddis.gsfc.nasa.gov) and then processed for com- TEC (e.g., Nishihashi et al. 2009; Aggarwal 2015; putation of total electron content. The data for the Sunil et al. 2015). Periodic structures in seismic- induced TEC anomalies have also been reported (Oikonomou et al. 2016). In India, many results have been reported on the earthquake-induced ionospheric perturbations using GPS-TEC mea- surements (Singh et al. 2009; Priyadarshi et al. 2011a, b), VLF measurements (Maurya et al. 2013) and ionosonde measurements (Sripati et al. 2020). Using an electrodynamic model for atmosphere– ionosphere coupling, Sorokin et al. (2006) explained that the emanation of radon and other gases over the earthquake preparation zone may cause the generation of acoustic gravity waves. They further reported that large amount of ema- nation of these gases may cause generation of Figure 1. Map showing location of the earthquake epicenter anomalous electric Beld which can produce large- (by * with red colour), circle of earthquake preparation zone scale changes in ionosphere-electrodynamics. and ionospheric measuring GPS station (by + with blue color for Ndoi EQ and green color for Indonesian EQ). Blue circle In the present study, an attempt has been made indicates the earthquake preparation zone. This circle is drawn to analyze ionospheric perturbations caused by the by assming epicenter as a center and radius of erathquake two major earthquakes: (i) Indonesian Earthquake preparation zone as a radius. J. Earth Syst. Sci. (2021) 130:149 Page 3 of 15 149 Table 1. List of GPS stations considered for ionospheric perturbation analysis and location of epicentre for Indonesian Earth- quake of 24 June 2019. In the table ‘I’ stands for increase and ‘d’ stands for decrease. The number put before I and d indicate number of days from the main shock. EQ details: Date: 24-06-2019 Magnitude: 7.3, 292 km NW of Saumlaki, Indonesia Epicenter: Latitude: 6.4088S, Longitude: 129.1698E Occurrence UT: 02:53:39 (11:53:39 LT) Ionospheric perturbation Distance of GPS GPS stations with geographic IGS station from Before main After main coordinate code epicenter (km) Azimuth shock shock Kathrine, Australia KAT1 943 339.5° None None 14.376°S, 132.153°E Darwine, Australia DARW 747 341.85° None None 12.843°S, 131.132°E Benoa, Indonesia BNOA 1559 81.38° (1-2)-I 5-I 8.746°S, 115.209°E Quezon City, Philippines PIMO 2503 14.02° 3-d, (1-2)-I, 0-d 1-I, d 3-d(4-5)-I, d 14.635°N, 121.077°E Cape Ferguson, Australia TOW2 2404 112.3° None None 19.269°S, 147.055°E Puerto Princesa, Philippines PPPC 2137 10.82° 5-d,(2-3)-I,0-d 1-d, 4-I, 5-d 9.772°N, 118.74°E Lombrum, Papua New Guinea PNGM 2074 80.04° (1-5)-I (1-2)-I, 5-I 2.043°S, 147.366°E selected stations are subjected to statistical anal- The other source is from the Total Ozone Map- ysis to Bnd out presence of anomaly from day-to- ping Spectrometer (TOMS) based on a NASA day variations. The hourly mean values of VTEC satellite instrument. The instrument measures the (Vertical Total Electron Content) for 5 days before total column amount of atmospheric ozone NO2 as and after the earthquake are considered and well as lower atmospheric dust, smoke, and other anomalies in the data from the monthly average aerosols. Thus it can distinguish between aerosol variation are selected for further analysis. For types such as smoke, dust and sulphates. In this anomalous variations, an upper bound (UB) study, total ozone column (TOC) daily data pro- (TEC ðMMÞþ1:34r) and the lower bound (LB) duct (OMDOAO3e˙003˙ColumnAmountO3) with (TECðÞÀ MM 1:34r) are computed, where TEC 0.25°90.25° resolution is taken from https:// (MM) and r are the monthly median and standard giovanni.gsfc.nasa.gov/giovanni/.