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Guide

Tsunami: what to do

Checked September 17, 2026 against the California Geological Survey, Del Norte County, the Redwood Coast Tsunami Work Group and the National Tsunami Warning Center; the statewide parts checked September 24, 2026 against the California Geological Survey and Cal OES.

The Tsunami tile repeats what the National Tsunami Warning Center has said. This page is about the tsunami it cannot warn you about in time — the one that starts just offshore, where the shaking is the warning and the first surges can arrive within minutes. That is true on every board on this coast, from Fort Dick to Imperial Beach; what differs is the fault.

If the ground shakes hard, or for a long time, do not wait for anything. Drop, cover and hold on until it stops, then go to high ground or inland, on foot. The California Geological Survey: “If strong shaking lasts for 20 seconds or more, everyone within the tsunami evacuation area should evacuate as soon as it is safe to do so.” Do not wait for a phone alert, a siren or this website.

Two completely different events

A distant tsunami starts far away, across the Pacific or off Alaska. There are hours, warnings are issued, and the tile turns. The whole state knows that one. The California Geological Survey puts the damage from the 2011 Tōhoku tsunami in California at more than $100 million, “primarily in coastal harbors and ports”: about $28 million at Crescent City, and about $28 million at Santa Cruz, where fourteen boats sank. A distant tsunami does its worst in harbours, as currents and surges, and often while the beach looks quiet.

A local tsunami starts close by: an earthquake on a fault under or just off the coast, or an underwater landslide. The Survey is plain that for one of those “there won’t be time for an official warning.” Its examples include a magnitude 7 to 8 earthquake on the offshore Ventura–Pitas Point fault zone off Ventura County, and an underwater landslide in Monterey Canyon reaching the Santa Cruz County shore within minutes. Each board’s Tsunami tile names its own coast’s nearby faults.

The north coast: Cascadia

Del Norte and Humboldt counties face the Cascadia Subduction Zone, and this section is theirs. The north coast knows the distant tsunami well too. On March 28, 1964, after a magnitude 9.2 earthquake in Alaska, the California Geological Survey records that “several surges reaching 21 feet high swept into Crescent City four hours after” the quake: ten people died and half the waterfront business district was destroyed. (A NOAA report on Crescent City puts the deaths at twelve.) In 2011 the tsunami from the Tōhoku earthquake in Japan caused $28 million in damage in Del Norte County.

Here the local tsunami comes from the Cascadia Subduction Zone, which runs just offshore. The Geological Survey’s own figures for the north coast: a big Cascadia earthquake “might cause five to six minutes of shaking and give people along the coast a maximum of 10 minutes to get inland or to high ground.” It could send surges “up to 50 feet high toward Crescent City and 30 feet high along the outer coast of Humboldt Bay.”

So this tile is useful for one of those two events and too slow for the other. No alert can be counted on to reach you, and you to reach high ground, inside ten minutes. The shaking is the alert.

The natural warning

The Redwood Coast Tsunami Work Group puts it simply: “The longer the shaking, the more likely a tsunami could be on its way. The shaking could be weak or strong – the important signal is duration!” And on which warning to trust: “Natural and Official Warnings are equally important. Respond to whichever you experience first.”

Go on foot if you can; after a big earthquake the roads may be damaged or jammed. A tsunami can last for several hours, and later surges can be bigger than the first, so stay on high ground until officials say it is over.

The maps are the part worth doing before you need them

The state’s Tsunami Hazard Area maps, from the California Geological Survey and Cal OES, show “areas that could be exposed to tsunami hazards during a tsunami event”, and they cover every county with a board here: the Survey finished the mainland coast and Catalina Island in October 2022, and says the rest of the Channel Islands will follow. There is a page for each county, and a map viewer that takes an address; one look at home is worth more than any alert. Humboldt County’s were released on August 13, 2020 and Del Norte County’s on March 11, 2021. They are drawn from a 975-year probabilistic model and then extended for local sources the model does not cover, and they are for evacuation planning: the Survey says they are not legal documents and are not for real estate disclosure.

On the north coast, the community evacuation maps from the Redwood Coast Tsunami Work Group turn that into streets. There are maps for Crescent City, Fort Dick, Klamath and Smith River in Del Norte County, and for Orick, Big Lagoon, Trinidad, McKinleyville, Arcata, Manila, Samoa, Eureka, Fairhaven, Fields Landing, the Eel River area and Shelter Cove in Humboldt County. Their rule: if you are in the yellow area, plan a safe route to the nearest green. For a place not on that list, look up the address in the state’s map viewer.

Getting an official alert

Every California county runs its own emergency alerts, and you generally have to sign up in advance. Cal OES keeps each county’s sign-up in one list. Sign up for the county you live or stay in.

The sign-up for each county with a board here, north to south, as Cal OES links it (read September 26, 2026): Del Norte, Humboldt, Mendocino, Sonoma, Marin, Napa, Solano, Contra Costa, Alameda, San Francisco, San Mateo, Santa Cruz, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange, San Diego.

On the north coast, Del Norte County’s alerts come through the Del Norte Community Alert System, and the county is plain that “this is an opt-in system, so you must register in advance to receive notifications.” Humboldt County runs its own emergency notifications, linked below. Just remember what an alert is for: the distant tsunami, which gives time. For the local one, the shaking comes first.

What the alert levels mean

Sources