Abnormal variation of thermosphere atmospheric density during the period of big earthquake

Earthquake is the natural disaster that human beings are most concerned about, while the influence of earthquake on the density of the thermosphere is not clear. Recently, it was occurred a class of 8.0 big earthquake on May 12, 2008 in Wenchuan City, Sichuan province in China. Later, a series of big earthquake events with the class 7.0~7.6 happened in the east of Honshu in Japan on June 14, Okhotsk on July 5 and the east seacoast of Honshu on July 19. During the course of earthquake events, an atmospheric density detector on board of the solar synchronous satellite at the orbital altitude of 630 km worked all the time and got a large quantity of in-situ measurement data. According to the data, it was discovered that the abnormal atmospheric density decrease over the center region of the earthquake source on the earthquake day. During the period about 1~3 days before the strong earthquake, the decrease of upper atmospheric density has been existed and reached the valley on the earthquake day with the decreasing ratio ranging from 0.40 to 0.65. Furthermore, the range of the decrease located at the latitude of ± 3 º~±9 º from the earthquake center before the earthquake, but it expanded to about ± 8 º ~±20 º from the earthquake center on the earthquake day.