Tsunami Safety After an Earthquake

In deep ocean water, tsunamis travel at speeds comparable to a commercial jet — up to 800 km/h (500 mph). As they approach shallow coastal water, they slow dramatically but grow in height. This means communities far from the earthquake epicenter can have warning time of hours, while those nearby may have only minutes.

In the open ocean, tsunamis may be barely noticeable — less than 1 meter. Near shore, they can reach heights of 10-40 meters. The 2011 Japan tsunami reached 40.5 meters at one location. Height depends on seafloor topography, coastal geometry, and the energy of the earthquake.

Never. "Tsunami tourism" — staying to photograph incoming waves — has killed people in multiple events. By the time a tsunami wave is visible, you have seconds, not minutes, to survive. The 2004 Indian Ocean tsunami killed numerous observers who stayed to watch what they initially thought was the ocean receding for an unusual reason.

Tsunamis vary enormously by location and source. The 2011 Tohoku tsunami reached 40 meters in some locations along Japan's Sanriku coast. Most damaging tsunamis are 5-20 meters. Wave height depends on offshore earthquake magnitude, seafloor topography, and coastal geometry. Elevation of 30+ meters (100 feet) above sea level provides safety from most documented tsunamis.

No. Tsunamis typically arrive as a rapid surge or receding tide rather than a curling wave. Before a tsunami, the sea may dramatically recede, exposing the seafloor — this is a warning sign, not an opportunity to investigate. The most dangerous wave in a tsunami series is often not the first but the second or third.