Tsunami can cause severe damage to properties and loss of many human lives. Tsunami is often related to earthquakes. Within a close proximity and with similar magnitude, some earthquakes produce very severe tsunamis, e.g. the December 2004 Sumatra earthquake, and others produce very minor or insignificant wave height increase, e.g. the March 2005 Sumatra earthquake. Thus, the study of tsunamigenesis of earthquakes, i.e., whether an earthquake will generate significant tsunami, is critical to the prevention or minimization of damage due to tsunami. In this study, the seismic signals from earthquakes were analyzed in order to determine tsunamigenesis more accurately. Fast Fourier Transform (FFT) of the seismic signals of the earthquakes was performed for a number of historical earthquake records of both tsunamigenic and non-tsunamigenic earthquakes of similar magnitude and epicenter distance. The results showed that tsunamigenic earthquakes have lower amplitude in the high frequency range (0.15–0.3 Hz) as compared to non-tsunamigenic earthquakes. Preliminary wavelet analysis of these earthquakes also revealed that the intensity pattern of tsunamigenic and non-tsunamigenic earthquake was similar to the findings from FFT. Both techniques lead to the conclusion that the long period signal and the depletion of high frequency energy revealed in the seismic signal may well indicate the tsunamigenic potential of the earthquakes. Thus the techniques that analyze the frequency content of the seismic signals have a great potential to complement the existing Pacific Tsunami Warning System, which only takes the magnitude of earthquake as the determining factor in predicting the generation of tsunami.