A tsunami is a series of waves often generated by a large undersea earthquake that displaces the ocean floor. A tsunami can also be caused by an underwater landslide or volcanic eruption. Because tsunamis travel extremely fast in the deep ocean, a tsunami from a distant source hundreds or even thousands of miles away can reach San Francisco Bay shoreline in a matter of hours.

The first wave is almost never the largest or worst. In fact, tsunami surges can last for many hours, carrying harmful, damaging debris and leaving areas flooded. 

What to do before a Tsunami Hits 

You DON'T want to be in a Tsunami Hazard Zone when a tsunami is coming. In the event a Tsunami Warning is issued by Federal, State, or local authorities:

• Go to high ground or inland! Keep going until you are out of the Tsunami Hazard Zone.
• Stay there! Wait for the "all clear" from a reliable source. Tsunami waves may arrive for hours

While most Bay Area earthquakes do not create tsunamis, a major earthquake could cause a seiche. A seiche ("pronounced saysh") is a wave that travels back and forth in a body of water. Like sloshing water in a bathtub, the wave returns repeatedly.

If a major earthquake occurs, go to high ground or inland and stay there! The shaking is your Tsunami Warning.

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