Electric and magnetic field perturbations recorded by DEMETER satellite before seismic events of the 17th July 2006 M 7.7 earthquake in Indonesia

Seismo-electromagnetic phenomena refers to the electric and magnetic field perturbations that may be caused due to geophysical activities like earthquakes and volcanic eruptions. Due to the existence of such phenomena before earthquakes they may be regarded as short term precursors to earthquakes. Keeping in mind the in situ measurements for detection of such phenomena, the satellite based techniques are of great interest because they keep a constant track of the seismically active zones globally. With the objective of detecting the electromagnetic emissions in the ionosphere, the DEMETER satellite has been launched on 29th June 2004 from Baikonour in order to study the ionospheric perturbations associated with seismic activities. In this paper, we discuss some interesting results of electromagnetic emissions that are observed before a series of recent Indonesian earthquakes in the Jawa region with a major shock measuring 7.7 magnitude on Richter scale which occurred on 17 July 2006. The emissions have been observed in the Ultra Low Frequency (ULF)/Extremely Low Frequency (ELF) range of electromagnetic spectra.