GPS based total electron content (TEC) anomalies and their association with large magnitude earthquakes occurred around Indian region

Transcription

1 Indian Journal of Radio & Space Physics Vol 42, June 2013, pp GPS based total electron content (TEC) anomalies and their association with large magnitude earthquakes occurred around Indian region O P Singh 1, $,*, Vishal Chauhan 1 & Birbal Singh 2 1 Department of Physics, Faculty of Engineering & Technology, R B S College, Bichpuri, Agra , India 2 Department of Electronics & Communication Engineering, Faculty of Engineering & Technology, R B S College, Bichpuri, Agra , India $ opsasd@gmail.com Received 27 August 2012; revised 7 March 2013; accepted 11 March 2013 In this paper, the effect of earthquakes on total electron content (TEC) data at Agra (geographic latitude 27.2 N, longitude 78 E), India has been examined. This study has been carried out for a period of 30 months from 01 January 2009 to 30 June 2011 and a dual frequency GPS receiver system is used for recording TEC data. To investigate the seismic effects on TEC, an epicentral distance of 2000 km from the observing station has been selected. This region includes 22 cases of earthquakes during the period of study with large magnitudes (M 5.5). Different statistical procedures are used to observe the anomalies in TEC data. The results show that TEC fluctuated in the form of enhancements and depletion and maximum precursors are found 5-10 days prior to these earthquakes. The solar and geomagnetic activities during the cases of earthquakes have also been studied and data on disturbed days are omitted to separate out the seismic effects. Hence, the observed TEC anomalies may be due to the occurrences of large magnitude earthquakes around Indian region. The E B drift due to the electric field generation during earthquake preparation process and ground wave oscillations may possibly be the significant contributors of these anomalies in TEC data. Keywords: Earthquake, Total electron content (TEC) anomaly, GPS based TEC PACS Nos: Ls; pc; Fc 1 Introduction In many of recent research works, a convincing association between ionospheric perturbations and seismic events has been reported by several researchers 1-7. The seismo-ionospheric relations are detected through different ionospheric parameters like the greatest plasma frequencies in the ionospheric F 2 region (fof 2 ) and E region (foe s ), subionospheric very low frequency (VLF), fixed frequency transmitter signals, ionospheric electron density measurements, total electron content (TEC), etc Out of these ionospheric parameters, total electron content (TEC) data are used widely for earthquake precursory studies The global positioning system (GPS) based TEC provides an overall description of the ionization and is measured in TEC units, where one TECU is equal to el m -2. In this paper, the association of TEC data with earthquakes occurred in an epicentral distance of 2000 km from the observing station has been studied. This region includes 22 cases of earthquakes in the period of study with large magnitudes (M 5.5). The results show that TEC fluctuated in the form of enhancement and depletion; and maximum precursors are found 5-10 days prior to these earthquakes. 2 Experimental setup The experimental setup for TEC measurements at Agra is similar to that used in previous works 7,9,20. Briefly, a dual frequency ( and MHz) GPS receiver system (GSV4004B) has been employed at Agra station for the measurements of TEC. This system is obtained from GPS Silicon Valley, USA and includes an L1/L2 GPS antenna (Novatel s Model GPS 702), a GPS receiver (Novatel s Euro Pak 3-M), and necessary softwares. The TEC data are obtained at 1 min sampling rate. The TEC measurements are being carried out through combined frequencies pseudorange and carrier phase measurements. The instrumental biases such as receiver and satellite biases are taken care of prior to final TEC calculations Retrieval of data and Method of analysis The continuous measurements of TEC data using above mentioned GPS receiver are in progress at Agra station since 24 June The TEC data obtained are slant TEC which are recorded at a sampling rate of 60 seconds. From this data, vertical TEC (VTEC) values are obtained at different ionospheric pierce

2 132 INDIAN J RADIO & SPACE PHYS, JUNE 2013 point (IPP) locations by using a mapping function 21,22, i.e.: R Ex cos( E) S( E) = = 1- Cos(z) R E + hs where, R E, is the mean radius of the earth in km; h S, the ionosphere (effective) height above the earth s surface; z, the zenith angle; and E, the elevation angle in degrees. The ionospheric height is taken as 350 km and TEC values are taken at higher elevation angles > 50 to avoid the effect of troposcatter, multipath, etc. 23. Since many TEC values are obtained at a time from different satellites, a running average is taken to get a single curve for a day. To eliminate the effect of magnetic storms on TEC data, the details of quiet and disturb days, and corresponding D st index data are obtained from the website of World Data Center, Kyoto, Japan, To investigate the anomalous variations in VTEC data, a 15 days backward running mean (m) and running standard deviation around mean (m±2σ) are calculated and the variation of VTEC is plotted between the curves of m ± 2σ. The values of VTEC crossing m ± 2σ curves are said to be abnormal. 4 Results and Discussion It has already been mentioned that the TEC measurements using a dual frequency GPS receiver has been in progress at Agra station since 24 June Here, the TEC data for a period of 30 months from 01 January 2009 to 30 June 2011 has been studied to find their association with large magnitude earthquakes (M 5.5) occurred within an epicentral distance of 2000 km from the observing station Agra. The locations of the epicenters of the earthquakes in the map of India and around and the observing station Agra are shown in Fig. 1. For brevity in the paper, here two cases of the earthquakes are presented which occurred on 07 November 2009 and 08 December The analysis shows that the VTEC values fluctuate in the form of enhancements and depletion. TEC data for the earthquake of 07 November 2009 is shown in Fig. 2. In this figure, the dark solid line indicates the variation of VTEC data for a period of 31 days and dashed curves show the variation of m±2σ for the same period. The inverted arrow indicates the day of the occurrence of earthquake. As seen from the data of VTEC, there are unusual enhancements identified on 28 November 2009 about 10 days before the occurrence of the earthquake. These anomalies cannot be attributed to magnetic storms because the data on disturbed days has already been omitted. Hence, this unusual variation of TEC may be correlated with the earthquake of M=5.6. The data corresponding to the other case of earthquake (M=5.5) occurred on 08 December 2010 is shown in Fig. 3. Here, also a pronounced peak in the raw VTEC data is observed on 06 December 2010, two days before the occurrence of the earthquake. Since geomagnetic conditions are also quiet during this month, the unusual enhancement in the data can be attributed to the seismic event of 08 December The mechanism of coupling between the lithosphere activity and ionosphere has been proposed elaborately by Hayakawa et al. 24,25. They proposed three coupling channels: (i) chemical channel, (ii) acoustic channel, and (iii) electromagnetic channel. Out of these, the electromagnetic channel is found to be insufficient because of weak intensity of lithospheric radio emissions 26. The explanation of physical model of chemical channel is given in Pulinets & Boyarchuk 4, Pulinets & Liu 27 and Sorokin et al. 28. Pulinets 29 has proposed that the radon emission ionizes the near earth atmosphere over the seismic zone. He suggested formation of quasi-neutral ion-clusters as a first state of seismo-ionospheric coupling and then the generation of electric field in Fig. 1 Map of India and adjacent region depicting the locations of epicenter of the earthquake (M 5.5) occurred within epicentral distance of 2000 km; observing station Agra shown by star

3 SINGH et al.: GPS BASED TEC ANOMALIES AROUND INDIAN REGION 133 Fig. 2 Variation of VTEC (solid lines in red) for a period of 31 days between 23 October and 22 November 2009 corresponding to the earthquake of 07 November 2009; dashed curves indicate m±2σ for the same period; inverted arrow indicates the day of the occurrence of earthquake; dashed circle highlights the observed anomalous day in VTEC data Fig. 3 Variation of VTEC (solid lines in red) for a period of 15 days from 01 December to 15 December 2010 corresponding to the earthquake of 08 December 2010; dashed curves indicate m±2σ for the same period; inverted arrow indicates the day of the occurrence of earthquake; dashed circle highlights the observed anomalous day in VTEC data

4 134 INDIAN J RADIO & SPACE PHYS, JUNE 2013 the next stage. On the other hand, the acoustic channel is based on the key role of atmospheric oscillations in the lithosphere-atmosphere-ionosphere coupling, and the perturbation in the Earth s surface (such as temperature, pressure) in a seismo-active region excites the atmospheric oscillations traveling up to the ionosphere, which causes the ionospheric density perturbations Conclusions The GPS based TEC data are analyzed for the period of 30 months from 01 January 2009 to 30 June 2011 in the light of magnetic storms and earthquakes. The large magnitude earthquakes (M 5.5), which occurred within an epicentral distance of 2000 km from the observing station, Agra, are considered for this study. Anomalous variations in TEC, in the form of enhancements and depletions, are observed in almost all the cases of earthquakes examined with precursory period lying between 0 and 10 days. Since the data on disturbed days are omitted to investigate the seismic effects on TEC data, hence, the observed anomalies in TEC data may be due to the considered seismic events. The observed anomalies are interpreted in terms of electric field generation and ground wave oscillations during earthquake preparation process. Acknowledgement The authors are thankful to the Ministry of Earth Sciences (MoES), Government of India, New Delhi for providing necessary funds for this research work in the form of a major research project. References 1 Hayakawa M & Fujinawa Y, Electromagnetic phenomena related to earthquake prediction (Terra Sci Pub, Tokyo), Liu J Y, Chuo Y J & Chen Y I, Ionospheric GPS TEC perturbations prior to the 20 September 1999, Chi-Chi earthquake, Geophys Res Lett (USA), 28 (2001) pp Hayakawa M & Molchanov O A, Seismo-electromagnetics: lithosphere-atmosphere-ionosphere coupling (Terra Sci Pub, Tokyo), Pulinets S A & Boyarchuk K, Ionospheric precursors of earthquakes (Springer, Berlin), Kamogawa M, Pre-seismic lithosphere-atmosphereionosphere coupling, EOS Trans Am Geophys Union (USA), 87 (40) (2006) pp 417, doi: /2006EO Rishbeth H, Ionoquakes: Earthquake precursors in the ionosphere, EOS Trans Am Geophys Union (USA), 87 (32) (2006) pp Singh O P, Chauhan V, Singh V & Singh B, Anomalous variation in total electron content (TEC) associated with earthquakes in India during September 2006 November 2007, Phys Chem Earth (UK), 34 (2009) pp Chauhan V, Singh O P, Kushwah V, Singh V & Singh B, Ultra-low-frequency (ULF) and total electron content (TEC) anomalies observed at Agra and their association with regional earthquakes, J Geodyn (UK), 48 (2009) pp Liu J Y, Chen Y I, Pulinets S A, Tsai Y B & Chuo J Y, Seismo-ionospheric signatures prior to M 6.0 Taiwan earthquakes, Geophys Res Lett (USA), 27 (2000) pp Singh O P & Singh B, Ionization enhancements in sporadic E-layers prior to some major Indian earthquakes, J Atmos Electr (Japan), 24 (2) (2004) pp Tsai Y B, Liu J Y, Ma K F, Yen H Y, Chen K S, Chen Y I & Lee C P, Preliminary results of the istep program on integrated search for Taiwan earthquake precursors, Terr Atmos Ocean Sci (Taiwan), 15 (3) (2004) pp Hayakawa M, Lower ionospheric perturbations associated with earthquakes, as detected by sub-ionospheric VLF/LF radio waves, in Electromagnetic phenomena associated with earthquakes, Ed: M Hayakawa (Transworld Research Network, Trivandrum, India), 2009, pp Calais E & Minster J B, GPS detection of ionospheric perturbations following the January 17, 1994, Northridge earthquake, Geophys Res Lett (USA), 22 (1995) pp Devi M, Barman M K, Barbara A K & Depueva A, Total electron content near anomaly crest as precursor of earthquake, Indian J Radio Space Phys, 30 (2001) pp Devi M, Barbara A K & Depueva A Association of total electron content (TEC) and fof 2 variations with earthquake events at the anomaly crest region, Ann Geophys (Germany), 47 (1) (2004) pp Otsuka Y, Kotake N, Tsugawa T, Shiokawa K, Ogawa T, Effendy, Saito S, Kawamura M, Maruyamat T, Hemmakom N & Komolmist T, GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake, Earth, Planets Space (Japan), 58 (2006) pp Zakharenkova I E, Shagimuratov I I, Krankowski A & Lagovsky A F, Precursory phenomena observed in the total electron content measurements before great Hokkaido earthquake of September 25, 2003 (M=8.3), Stud Geophys Geod (Czechoslovakia), 51 (2) (2007) pp Liu J Y, Chen Y I, Jhuang H K & Lin Y H, Ionospheric fof 2 and TEC anomalous days associated with M 5.0 earthquakes in Taiwan during , Terr Atmos Ocean Sci (Taiwan), 15 (3) (2004) pp Chauhan V & Singh O P, A morphological study of GPS- TEC at Agra and their comparison with IRI model, Adv Space Res (UK), 46 (2010) pp Chauhan V, Singh O P & Singh B, Diurnal and seasonal variation of GPS-TEC during a low solar activity period as observed at a low latitude station Agra, Indian J Radio Space Phys, 40 (2011) pp Mannucci A J, Wilson B D & Edwards C D, A new method for monitoring the earth s ionospheric total electron content using the GPS global network, Proceedings of ION GPS-93 (Inst of Navigation, USA), 1993, pp

5 SINGH et al.: GPS BASED TEC ANOMALIES AROUND INDIAN REGION Langley R, Fedrizzi M, Paula E, Santos M & Komjathy A, Mapping the low latitude ionosphere with GPS, GPS World (USA), 13 (2) (2002) pp Rama Rao P V S, Niranjan K, Prasad D S V V D, Gopi Krishna S & Uma G, On the validity of the ionospheric pierce point (IPP) altitude of 350 km in the equatorial and low latitude sector, Ann Geophys (Germany), 24 (2006) pp Hayakawa M, Molchanov O A & NASDA/UEC team, Achievements of NASDA s Earthquake Remote Sensing Frontier Project, Terr Atmos Ocean Sci (Taiwan), 15 (2004a) pp Hayakawa M, Molchanov O A & NASDA/UEC team, Summary report of NASDA s earthquake remote sensing frontier project, Phys Chem Earth (UK), 29 (2004b) pp Molchanov O A, Mazhaeva O A, Goliavin A N & Hayakawa M, Observations by the Intercosmos-24 satellite of ELF-VLF electromagnetic emissions associated with earthquakes, Ann Geophys (France), 11 (1993) pp Pulinets S A & Liu J Y, Ionospheric variability unrelated to solar and geomagnetic activity, Adv Space Res (UK), 34 (2004) pp Sorokin V M, Yashchenko A K & Hayakawa M, Electric field perturbation caused by an increase in conductivity related to seismicity-induced atmospheric radioactivity growth, J Phys Chem B (Russia), 1 (2007) pp Pulinets S A, Ionospheric precursors of earthquakes: Recent advances in theory and practical applications, Terr Atmos Ocean Sci (Taiwan), 15 (3) (2004) pp