IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS010 Poster presentation 2089
Analysis of ionospheric electrostatic turbulence over seismic regions using
DEMETER plasma and wave measurements
Dr. Tatsuo Onishi
Jean-Jacques Berthelier
Several recent results have pointed out the existence of ionospheric disturbances associated with
seismic activity. Of great interest, in particular, is the possible occurrence of disturbances prior to the
main shock that can be thought as ionospheric precursors of earthquakes. One of the goals of the
DEMETER mission is to perform an in-situ study of the ionospheric plasma and waves in order to search
for events associated to seismic activity and to characterize pre- and post-seismic effects. Using
measurements of the electric components of plasma waves in the ULF/ELF/VLF ranges provided by the
ICE instrument and thermal plasma measurements from the IAP instrument, we have studied the
natural emissions that are observed over seismically active regions with an initial focus on the low
frequency electrostatic turbulence and plasma irregularities. The electromagnetic interferences onboard
DEMETER have been maintained to a low level. However, it is expected that events associated with
seismic activity have a weak intensity, and we have paid a careful attention to detect the occurrence of
electromagnetic interferences, understand their origin and estimate their effect on power spectra.
Similarly we have tried to recognize as far as possible natural emissions that arise from space weather
effects and are not linked with seismic activity in order to minimize their impact on the statistical
distribution of low level signals. In order to distinguish the true pre-seismic events from post-seismic
disturbances, a number of earthquakes were carefully selected from the earthquake database so as not
to include other seismic events of significant importance during the 5 preceding days within the same
seismic region. In this talk we shall present the most important aspects of the methodology that have
been followed to analyze the data and discuss current results from this on-going study.
Keywords: demeter, vlf, electrostatic