What is a tsunami?

A series of waves or surges that is most often caused by earthquake fault movement beneath the sea floor.

Tsunamis can trick you!

  • The first surge is not the largest.
  • It is not unusual for tsuami surges to last at least 12 hours and in some cases much longer.
  • Just when you think it is all over, another very large surge may come.

What areas are at risk?

Beaches, harbors, bays, and river mouths are at the greatest risk. If you are in the YELLOW areas of our Hazard Zone Maps, you should leave after feeling an earthquake that lasts a long time. If you are in the white area, stay where you are.

How do I know if an earthquake is big enough to cause a tsunami?

  • If you are on the beach and feel an earthquake, no matter how small, move inland or to high ground immediately.
  • If you are in a tsunami hazard zone and feel an earthquake that lasts a long time, evacuate as soon as it is safe to move. Not sure if the earthquake is long enough? When in doubt, DRILL IT OUT. Every earthquake is an opportunity to practice evacuating.
  • GO ON FOOT. Roads and bridges may be damaged by strong ground shaking. Avoid downed power lines. If evacuation is impossible, go to the upper floor of a sturdy building or climb a tree — but only as a last resort.

To read more about tsunamis: 

Visit our Frequently Asked Questions


Marigram (water level recording) from Crescent City during the 2011 Japan tsunami.  

Each horizontal dashed-line is 12 hours. Each vertical dashed-line is about 1.5 feet. The tidal fluctuation (blue line) affects the total water height. For example, a tsunami arriving on a high tide will cause more innundation and damage than on a low tide." This graphic probably needs a little more explanation which can be done at a later date.

Water level recording from Crescent City during the 2011 Japan tsunami.