Wavelet analysis of the seismograms of the 2004 Sumatra‐Andaman earthquake and its application to tsunami early warning

We applied the wavelet transform in an attempt to detect long‐period components early in a seismogram. We analyzed the displacement seismograms of the 26 December 2004 Sumatra‐Andaman earthquake (Mw = 9.2) and the 28 March 2005 Nias earthquake (Mw = 8.7). Wavelet analysis is able to clearly distinguish the amplitudes of the long‐period W phase between the seismograms of the two earthquakes before the S wave reaches the station. It shows that the 2004 earthquake generates a W phase of significantly greater amplitude. This facility has potential application to the rapid identification of truly great earthquakes with high tsunami potential.