2009 International Conference on Computers and Devices for Communication RSS 978-81-8465-152-2/09/$26.00©2009 CODEC Abstract— Electromagnetic fields due to earthquake have been studied in this presentation through some model calculations. The expressions of the variation of electron concentration and electron temperature as the ionospheric precursors of earthquake have been deduced in this presentation through quasihydrodynamic formulations. The outcome of the analyses of electromagnetic emissions recorded by VLF receivers at 5, 7, 9 and 12 kHz on November 16, 2008 over Kolkata (Lat. 22.56º N, Long. 88.5º E) during the large earthquake at Minahasa, Sulawesi (Lat. 1.27º N, Long. 122.09º E), under Indonesia have been presented here. Spiky variations of signals are observed few days prior to the day of occurrence of the earthquake which continued several days more, then decayed gradually and eventually ceased. Index Terms—Ionospheric perturbations, precursors of earthquake, seismicity, seismo-electromagnetics. I. INTRODUCTION OTH precursory and post- seismic variations in ELF- VLF amplitude and in ionospheric parameters have been reported from satellite based observations surrounding any earthquake [1]-[4]. The study of seismic related phenomena shows enhancement of DC electric field accompanied with the generation of periodic inhomogeneities in the electrical conductivity of the lower ionosphere. Significant perturbation in the electric field amplitude would be expected to occur in the lower atmosphere that enhances the changes in the values of lower atmospheric parameters [5]. The expressions of the variation of electron concentration and electron temperature within the medium are derived through energy balance equation, continuity equation and ionization balance equation. The equations for fluctuations of electron temperature and Manuscript received September 4, 2009. The authors acknowledge with thanks the financial support from Indian Space Research Organization (ISRO) through S K Mitra Centre for Research in Space Environment, University of Calcutta, Kolkata, India, for carrying out the study. Corresponding Author: S. S. De (Address: S. K. Mitra Centre for Research in Space Environment, Institute of Radio Physics and Electronics, 1, Girish Vidyaratna Lane, Kolkata 700 009, India. Phone: +91-33-2350 5829 Fax: +91-33-2351 5828 E-mail: de_syam_sundar@yahoo.co.in ) electron density are derived. Also, the results of some significant observations by VLF receivers recorded over Kolkata at 5, 7, 9 and 12 kHz during the Minahasa, Indonesia earthquake occurred on November 16, 2008 will be presented. The effects of the vast earthquake (M=7.3) are exhibited through the occurrence of discrete spikes which were observed first on November 9, 2008 and continued upto November 23, 2008. Both number of spikes and their intensities as well as durations were found to be changed irregularly and reached the maximum value on the day of occurrence. The signatures ceased gradually and almost ended after November 23, 2008. These commencements may be considered to be precursory and post-seismic effects of this vast earthquake [6]. The records were taken at Kolkata which is about 2400 km away from the place of occurrence. The effects at 5 and 7 kHz have been found to be remarkably higher than at 9 and 12 kHz. The VLF signals are processed and being stored in a computer. The r.m.s. value of the filtered data are analyzed regularly using Origin 5.0 software. II. MATHEMATICAL FORMULATIONS The effects of electromagnetic field due to earthquake on the variations of ionospheric parameters, the following equations are chosen: ) ( ) ( ) ( ) . ( 2 H v m eN v m p v T N t E N m e v v N t v N e e G G G G G G G G × - ∇ - ∇ - - - = ∇ + ∂ ∂ η ν (1) 0 ) ( ) ( 2 3 ) ( 2 3 = ∂ ∂ + ⋅ ∇ - - + ⋅ + ∂ ∂ t N Q W T T Nk T E v eN NkT t i e e e e G G G δν (2) } ) {( ) 1 ( 2 z N D D z N N N q t N t r de i ∂ ∂ + ∂ ∂ + + + - - + = ∂ ∂ α α λ α ν λ ν (3) On Some Effects of Perturbations in the Ionosphere due to Electromagnetic Precursory Signals from Earthquake S. S. De, B. K. De, B. Bandyopadhyay, Suman Paul, D. K. Haldar, S. Barui, Minu Sanfui, A. Bhowmick, Pinaki Pal, S. Nandi and T. K. Das B