Since an earthquake's fastest wave, its primary or P-wave, travels about 50 times faster than the fastest tsunami waves, a tsunami warning center will issue its initial tsunami warning based on seismic data alone. This animation uses the 9.1 magnitude Great Tohoku-Oki Earthquake and its tsunami to illustrate how the Pacific Tsunami Warning Center (PTWC) issued its first warning message less than 9 minutes after the earthquake and 19 minutes before the tsunami reached the first sea-level sensor not damaged by the earthquake, a deep-ocean or DART instrument. After the P-wave sequence the animation will then speed up to show the tsunami spreading through the world's oceans over a 48 hour period and highlight tsunami measurements by coastal and DART sensors.