Tsunami About

Earthquake, Tsunami & Volcano Programs
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A tsunami is a series of large ocean waves generated by either large, subduction zone earthquakes which deform the ocean floor or by landslides within or falling into the ocean. When the waves enter shallow depths near a coastline, they may rise to several feet or, in rare cases, tens of feet. If you are on a beach or in low coastal areas it is imperative you are aware that a tsunami could arrive within minutes after a severe earthquake. A tsunami’s danger period can continue for many hours after a major earthquake. Tsunamis can occur during any season of the year and at any time, day or night.

The California Governor’s Office of Emergency Services, Earthquake, Tsunami and Volcano Program is continuously researching, learning, and collaborating with science, industry, and academic experts to develop and confirm the latest, best available knowledge base to help make California’s residents and visitors safer in the event of tsunamic activity. By mapping potential inundation and evacuation areas, providing assistance in response and evacuation planning, implementing outreach, education and warning signage at the coast, as well as determining ways to improve preparedness and resilience of California’s ports and harbors, our staff strives to ensure everyone on the coast remains safe before, during and after the next tsunami.

​Causes of Tsunamis

A tsunami is a series of large ocean waves generated by either large earthquakes which deform the ocean floor, or landslides within or falling into the ocean. Any disturbance in the ocean that causes the displacement of large amounts of water could result in a tsunami. Not all earthquakes generate a tsunami. To generate tsunamis, earthquakes must occur underneath or near the ocean, be of a large magnitude, and create vertical movement of the sea floor. Generally, earthquakes on strike-slip faults, such as the San Andreas, do not by themselves generate tsunamis. In some instances, large strike-slip fault earthquakes may trigger landslides which could cause a local tsunami.

Most tsunamis are caused by earthquakes generated on a subduction zone, an area where one tectonic plate is forced under another plate. In subduction zones one plate is forced down and an adjacent plate is forced up causing an earthquake. The movement of the plates displaces water on the ocean floor vertically, resulting in a wave which then propagates horizontally through and across the entire ocean.

Eventually, water rushes landward and may flood the shoreline resulting in inundation of dry land. While