Ionospheric density variations recorded before the 2010 Mw 8.8 earthquake in Chile

We present a study of plasma density variations observed by the DEMETER spacecraft in the vicinity of a very powerful earthquake in Chile. This earthquake of moment magnitude 8.8 occurred on 27 February 2010 with an epicenter located at 35.85 degrees S, 72.72 degrees W. Data recorded 10-20 days before the main shock along orbits close to the future epicenter show increasing plasma densities. In a second step, a statistical analysis with DEMETER data has been performed using the first 3 months of the years 2007-2010 to monitor density variations in the vicinity of the epicenter at the same local time and seasonal conditions. This study shows that a large increase of the plasma density is very uncommon at this location and at this time and that the increases observed during the days before the main shock could be considered as possible short-term precursors of this powerful earthquake.