Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity

[1] We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by ∼2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes.

[1]  S. Pulinets,et al.  Ionospheric precursors of earthquakes , 2004 .

[2]  William H. Press,et al.  Numerical recipes in C , 2002 .

[3]  M. Johnston,et al.  On the reported magnetic precursor of the 1989 Loma Prieta earthquake , 2009 .

[4]  Ondrej Santolik,et al.  Spacecraft observations of electromagnetic perturbations connected with seismic activity , 2008 .

[5]  Ondrej Santolik,et al.  Decrease of intensity of ELF/VLF waves observed in the upper ionosphere close to earthquakes: A statistical study , 2009 .

[6]  J. Bortnik,et al.  The possible statistical relation of Pc1 pulsations to Earthquake occurrence at low latitudes , 2007 .

[7]  Katsumi Hattori,et al.  ULF Geomagnetic Changes Associated with Large Earthquakes , 2004 .

[8]  On the reported magnetic precursor of the 1993 Guam earthquake , 2009 .

[9]  M. Rycroft,et al.  Electromagnetic Atmosphere-Plasma Coupling: The Global Atmospheric Electric Circuit , 2012 .

[10]  早川 正士,et al.  Electromagnetic phenomena related to earthquake prediction , 1994 .

[11]  Craig J. Rodger,et al.  Investigating seismoionospheric effects on a long subionospheric path , 1999 .

[12]  Michel Parrot,et al.  Ionospheric perturbations linked to a very powerful seismic event , 2005 .

[13]  V. Sorokin,et al.  Electrodynamic model of the lower atmosphere and the ionosphere coupling , 2001 .

[14]  Katsumi Hattori,et al.  Ionospheric anomalies possibly associated with M ⩾ 6.0 earthquakes in the Japan area during 1998-2010: Case studies and statistical study , 2011 .

[15]  M. Parrot,et al.  Variation of the first cut-off frequency of the Earth-ionosphere waveguide observed by DEMETER , 2012 .

[16]  Cheng-Ling Kuo,et al.  Ionosphere plasma bubbles and density variations induced by pre‐earthquake rock currents and associated surface charges , 2011 .

[17]  Julia Ling,et al.  Air ionization at rock surfaces and pre-earthquake signals , 2009 .

[18]  C. Rodger,et al.  A search for ELF/VLF activity associated with earthquakes using ISIS satellite data , 1996 .

[19]  F. Leblanc,et al.  ICE, the electric field experiment on DEMETER , 2006 .

[20]  M. Rycroft,et al.  Atmospheric electricity coupling between earthquake regions and the ionosphere , 2010 .

[21]  M. Hayakawa,et al.  Observation by the Intercosmos-24 satellite of ELF-VLF electromagnetic emissions associated with earthquakes , 1993 .

[22]  U. Inan,et al.  A search for ELF/VLF emissions induced by earthquakes as observed in the ionosphere by the DE 2 satellite , 1993 .

[23]  K. G. Budden.  The Wave-guide mode theory of wave propagation , 1963 .

[24]  V. Migulin,et al.  Some statistical results on very low frequency radiowave emissions in the upper ionosphere over earthquake zones , 1989 .

[25]  Ondrej Santolik,et al.  Relationship between median intensities of electromagnetic emissions in the VLF range and lightning activity , 2010 .

[26]  F. Freund,et al.  Pre-earthquake signals: Underlying physical processes , 2011 .

[27]  Francois Lefeuvre,et al.  Electromagnetic ELF radiation from earthquake regions as observed by low‐altitude satellites , 1992 .

[28]  C. Liu,et al.  Giant ionospheric disturbances excited by the M9.3 Sumatra earthquake of 26 December 2004 , 2006 .

[29]  F. Lefeuvre,et al.  The magnetic field experiment IMSC and its data processing onboard DEMETER: Scientific objectives, description and first results , 2006 .

[30]  M. Parrot,et al.  Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes , 2012 .

[31]  W. Daily,et al.  Evidence of electro-seismic phenomena , 1989 .

[32]  Michel Parrot,et al.  Statistical study of ELF/VLF emissions recorded by a low‐altitude satellite during seismic events , 1994 .

[33]  H. Christian.  Global Frequency and Distribution of Lightning as Observed From Space , 2001 .

[34]  Masahisa Sugiura,et al.  An attempt to delineate very low frequency electromagnetic signals associated with earthquakes , 2001 .