In the 2004 Indian Ocean Tsunami, many people who don't know tsunamis were killed by the tsunami. It showed that disaster information is important to mitigate damage caused by tsunamis. To provide appropriate disaster information for the administrators and residents, a tsunami warning system is necessary. A reliability of the system depends largely on its capacity for detecting tsunamis. The present tsunami warning systems use observed seismic waves to detect tsunami source. Then, the present system has risk of underestimating tsunamis due to the great earthquakes of magnitude 9 class right after the main shocks. In this study, we show what tsunami disaster information would be provided, if the present tsunami warning system had been established in the Indian Ocean before 2004.