Statistical analysis of electron density anomalies before global M-w >= 7. 0 earthquakes (2005-2009) using data of DEMETER satellite

Based on the data of French DEMETER satellite, we attempt to make a statistical analysis of variations of electron density before 37 M-w >= 7.0 earthquakes in the world during January 2005 to December 2009. The orbits, recorded in local nighttime by the satellite, were chosen by a range of longitude 20 degree and latitude 15 degree during the 9 days around these earthquakes, with 7 days before and 1 day after. Among the 37 earthquakes, electron density perturbations were detected before 19 events, accounting for nearly 51% of the total. The anomalies represent positive before 18 events and occurred mostly within 1 similar to 6 days before the shocks, part of which appeared more than one time. It is more easily to observe the electron density disturbance around the equatorial and low-latitude regions than high latitudes. The disturbance amplitude presents a positive correlation with the magnitude of earthquakes basically, while the depth of earthquakes does not show significant relationship with the perturbation. It is noted that before several events, the anomalies were likely associated with the combined effect of earthquakes and geomagnetic activity and revealed a higher disturbance level. As the seismoionospheric coupling process is complex, it is necessary to conduct more observations of multi-parameters on the ground, in the atmosphere and ionosphere synchronously.