Since an earthquake's fastest wave, its primary or Pwave, 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 TohokuOki 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 sealevel sensor not damaged by the earthquake, a deepocean or DART instrument. After the Pwave 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.