Specific features of ionospheric total electron content variations in the periods of preparation of the earthquakes on March 11, 2011 (Japan) and October 23, 2011 (Turkey)

The main morphological features of variations of the total electron content (TEC) of the ionosphere before the earthquakes on March 11, 2011 (Japan) and October 23, 2011 (Turkey) are examined. The revealed features are compared to those of ionospheric TEC disturbances observed prior to several other large seismic events, as well as to those included in a list of the most frequently observed ionospheric TEC disturbances interpreted as possible ionospheric precursors of earthquakes. It is shown that, in the periods of preparation of the earthquakes under consideration, on March 8–11 and October 20–23, abnormal ionospheric TEC disturbances were observed as long-lived structures in a near-epicentral region and in the region magnetically conjugated to it.