Ionospheric disturbances before and after strong earthquakes based on DEMETER data

Using ion temperature (T_i), VLF electromagnetic field single-frequency spectrum data from DEMETER satellite, this paper studies variation of these parameters associated with the strong earthquakes: the Wenchuan M_S8.0 earthquake of China on 12 May 2008, the Haiti M_S7.3 earthquake on 12 January 2010 and the Chile M_S8.8 earthquake on 27 February 2010. The result for Wenchuan M_S8.0 earthquake shows that the ion temperature (T_i) northwest to the epicenter increased 3 days before the mainshock, and the data of VLF magnetic field spectrum below 200 Hz showed disturbance within 2° of the epicenter on May 8 before the mainshock. The result for the Chile M_S8.8 earthquake shows that the ion temperature (T_i) northwest to the epicenter showed fluctuation 9 days before the mainshock; on February 23 before the Chile earthquake the frequency range from 100 Hz to 160 Hz of VLF magnetic field spectrum showed sudden rise within the area of 5° around the epicenter. No obvious anomalies of the three parameters were observed before the Haiti earthquake, but after the mainshock some anomalies were found. T_i and the frequency band from 40—160 Hz of VLF electric field spectrum and the VLF magnetic field spectrum in the 120—480 Hz frequency band showed significant anomalies on the day of earthquake occurrence, which might be caused by energy release after the earthquake. Currently we have no evidence to conclude that these changes result from seismic activity, but in the data processing we have excluded the disturbances induced by solar activity and magnetic field to a certain degree, and the data selected are closely linked with the time and space of the earthquake. This result is consistent with previous research results, and we propose that the abnormities found in the paper may be related to the three strong earthquakes.