Abstract
Abstract. In Samoa Islands, a powerful earthquake took place at 17:48:10.99 UTC (06:48:10.99 LT) on 29 September 2009 with a magnitude Mw=8.1. Using ICE (Instrument Champ Electrique) and IMSC (Instrument Magnetic Search Coil) experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground-based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. In a previous study we have shown that anomalies in IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard the DEMETER and also TEC (Total Electron Content) data appear 1 to 5 days before the Samoa earthquake. In this paper we show that the anomalies in the VLF transmitter signal and in the HF range appear with the same time scale. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo-ionospheric precursors. It is also shown that comparative analysis is more effective in seismo-ionospheric studies.
Highlights
The preseismic perturbations in lithosphere, atmosphere and ionosphere without significant solar and geomagnetic disturbances are considered as hint of impending earthquakes
A dominant anomaly is observed in total ion density, electron density and ion temperature parameters measured by IAP and ISL sensors at ∼10:30 Local Time (LT), 4 days before the earthquake
Unusual TEC variations 4 days before the earthquake confirm the results deduced by the DEMETER data (Akhoondzadeh et al, 2010)
Summary
The preseismic perturbations in lithosphere, atmosphere and ionosphere without significant solar and geomagnetic disturbances are considered as hint of impending earthquakes. The thin layer of particles created before earthquakes due to ion radiation from the Earth has a main role in transferring electric field to above atmosphere and to the ionosphere The penetration of this electric field to the ionosphere was first analytically calculated in Park and Dejnakarintra (1973) and applied to the seismo-electromagnetic process by Kim et al (1994) and Pulinets et al (2000). Many papers and special monographs have been published on satellite observations of the ionospheric plasma, the flux of charged particles, the DC electric field, electromagnetic waves and geomagnetic field associated with seismic activity (Hayakawa and Molchanov, 2002; Pulinets and Boyarchuk, 2004).
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