Abstract
Abstract. We report on the analysis of ELF/VLF emissions observed by the Instrument Champ Electrique (ICE) experiment onboard the DEMETER micro-satellite. We consider principally selected seismic events reported by Molchanov et al. (2006). These authors studied the VLF signals radiated by ground transmitters and received on board the DEMETER micro-satellite. They revealed a drop of the signals (scattering spot) connected with the occurrence of large earthquakes. In our investigations, we proceed to a spectral analysis of ICE observations with the aim to find if the natural ionospheric VLF/ELF emissions show, or not, a similar ''drop'' in the intensity as it is the case of the VLF transmitter signal. We combine our results with those of Molchanov et al. (2006), and we discuss the origin of such interesting ionospheric features in the frame of the investigation of the pre-seismic electromagnetic emissions. We show that the geomagnetic activity is a key parameter which could disturb the natural VLF ionospheric emissions, and also the transmitter signal. We find that it is not possible to conclude the presence, or not, of a preseismic effect when the Kp-index is higher than one.
Highlights
Since more than twenty years detailed observations of electromagnetic signals occurring before seismic events have been reported
These disturbances were mainly derived from the ionosonde electron density measurements. This technique is found to be limited and difficult because of the local temporal and spatial coverage of the seismic regions. This limited area coverage is resolved by the use of ground-based receivers connected to the global positioning system (GPS) which is deployed to monitor the Earth’s surface deformation rates, and to provide continuously monitoring of the ionospheric total electron content (TEC) as described by Sardon et al (1994)
We investigate the electric field measurements recorded by the Instrument Champ Electrique (ICE) experiment, over the Adriatic seismic region, in November and December 2004
Summary
Since more than twenty years detailed observations of electromagnetic signals occurring before seismic events have been reported. Such precursors emissions have been found to cover a large frequency spectrum: ULF (Fraser-Smith et al, 1990; Molchanov et al, 1992; Hayakawa et al, 1996a), ELF/VLF (Gokhberg et al, 1982; Parrot and Lefeuvre, 1985), LF (Bella et al, 1998), and HF (Warwick et al, 1982) These first investigations had been supported by other observations and laboratory experiments as reviewed in Parrot (1995), Hayakawa and Molchanov (2002) and Molchanov and Hayakawa (2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
