Thesis (M.Sc.)--Chulalongkorn University, 2012

This research aims to observe the total electron content (TEC) variations after the earthquakes that magnitudes are greater than 7.5 and the depths of focus are less than 30 km beneath the ground surface during 2009-2011 using GPS data. There are six earthquake events which correspond to this research target. There are four out of six events that caused the TEC variations. Four earthquakes include the earthquake near the west coast of South Island in New Zealand, the earthquake in Samoa islands region, the earthquake near the east coast of Honshu in Japan and the earthquake in Kermadec Islands Region. The TEC variations were recorded by the GPS receivers near the epicenter zones. The GPS data provide the TEC data which was applied high pass filter in order to remove high frequencies. Then, the TEC data was smoothed using Savitzky-Golay method. Finally, the TEC data was analyzed power spectrum using fast fourier transform method in order to find the periods of the TEC variations. The results of this research show the time lags of the TEC variations are six minutes after the earthquakes origin times. The earthquakes generated the atmospheric wave called direct acoustic wave. The direct acoustic wave took six minutes from the ground surface to the ionosphere. The periods of TEC variations found in this study are 3.5 to 9.2 minutes which correspond to the periods of acoustic wave (2-10 minutes).