The risk of damaging flooding from a major tsunami may be greater than many realized along stretches of California’s renowned coastline, state officials say, further reinforcing the need for residents to take note if they live in or visit hazard areas.
The most recent risk assessment, outlined in maps that were published by the California Geological Survey and reviewed by The Times, illustrate the devastation that could result from scenarios considered to be extreme, but realistic. For instance, a large tsunami could flood swaths of Marina del Rey, Long Beach and the nearby dual port complex to an elevation of up to 15 feet above sea level.
A worst-case tsunami could bring flooding to sizable areas of Oakland, Berkeley and Alameda, up to 18 feet above sea level.
Flooding could reach up to 30 feet above the average high tide along the outer coast of Humboldt Bay and the Eureka area, and up to 50 feet toward Crescent City and Cayucos.
But for most Californians, the precise extent of tsunami risk is less important than knowing these hazard zones exist in the first place. The magnitude 7 quake Dec. 5 off the Humboldt County coast — which prompted a tsunami warning affecting millions in Northern California — was a blaring reminder of that.
Should a significant tsunami materialize, mere minutes could be the difference. Along California’s North Coast, some people might only have 10 minutes to get to an evacuation area following a huge earthquake just offshore.
“While damaging tsunamis are infrequent in California, they have and do happen. If you live on or visit the coast, you need to be aware of this potential hazard,” Steve Bohlen, then the head of the California Geological Survey, said when the updated tsunami hazard area maps were released.
To see if you live in a tsunami hazard zone, visit conservation.ca.gov/cgs/tsunami/maps.
The latest maps were published between 2020 and 2022. Though shunted out of the spotlight by other news events during that period, they are nevertheless notable — containing several major updates from earlier tsunami inundation maps that were published a decade earlier or more.
And with the state’s annual tsunami preparedness week set to start Saturday, officials say it’s vital for residents to familiarize themselves with their local risks.
The updates to California’s tsunami hazard areas followed a devastating tsunami in Japan in 2011, which was triggered by a magnitude 9.1 earthquake off the country’s eastern shore.
Prior to that disaster, Japan relied on data from several hundred years of records to estimate tsunami risk, which once “seemed perfectly reasonable,” according to Bohlen. But the disaster demonstrated the need for scientists to consider even rarer events — tsunamis that may only strike once every 1,000 years or so.
California, as a result, opted to take “a very conservative approach” for its maps, “hoping to avoid the tragic loss of life experienced in Japan,” Bohlen said in a prior statement.
There are a number of scenarios in which California could get hours of lead time ahead of a damaging tsunami. But should a quake strike close to shore, there could be little to no warning, aside from the shaking itself.
“The bottom line is, if you’re near the coast and feel strong shaking from a local earthquake or get an official notification to evacuate, move inland as soon as possible,” Rick Wilson, then a senior engineering geologist with the California Geological Survey tsunami unit, said in a statement in 2021.
In the latest update of the maps, potential tsunami flood areas were expanded in parts of Long Beach — including along Ocean Boulevard and Belmont Shore — Malibu, Santa Monica, Venice, Marina del Rey, Hermosa Beach, Redondo Beach and San Pedro.
Areas of notable concern in Los Angeles County include Marina del Rey, the ports of Long Beach and Los Angeles, and around Alamitos Bay because there are few roads for evacuation, according to the California Geological Survey.
Flooding to the extent considered possible in an extreme scenario “would inundate almost all of the land in the ports and some of the surrounding communities,” Wilson said when the latest maps were released.
In updating the maps, San Francisco also saw “significant increases in the mapped tsunami hazard” in the Financial District at the foot of Market Street, as well as parts of North Beach, south of the Embarcadero. The zone includes the Embarcadero BART and Muni stations and Embarcadero Center.
“These are both areas with very low land elevations that could be impacted by a small increase in waterfront flooding,” the geological survey said.
In many places, changes in the hazard maps were relatively modest. Some — like in Newport Beach — were expanded to add a small buffer beyond the modeled inundation area to roads or landmarks to help local officials communicate evacuation plans, the geological survey said.
“There are places on the U.S. West Coast, and here in Alaska, where an entire safe evacuation for a near-shore event … would [have] a much lower success rate,” said Dave Snider, the tsunami warning coordinator at the National Tsunami Warning Center in Alaska. “That is the No. 1 reason why people need to understand what their hazard zone is ahead of time.”
The changes went both ways. Some areas, such as around Huntington Beach and Bolsa Chica, saw their tsunami hazard areas shrink after new analysis indicated levees and ponds would help better protect the public than originally thought.
What became clear in the wake of December’s widespread warning was that many Californians had no idea where the tsunami warning zones were.
And, as the maps show, it’s not always areas right along the coast that are exposed. Tsunami hazard zones can extend to bayside and riverside areas relatively far from the Pacific coast, representing the maximum inundation area in a number of scenarios, according to the California Geological Survey.
California’s tsunami hazard areas are expansive in some areas, and include some of the state’s priciest real estate and most famed destinations: the Santa Monica Pier, Long Beach’s Naples Island, Newport Beach’s Balboa Island and Balboa Peninsula; and neighborhoods in Sunset Beach, Seal Beach, San Diego and nearby Coronado.
Also at potential risk are popular tourist hotspots from Malibu to Santa Barbara’s waterfront, the Monterey Bay Aquarium and a swath of Santa Cruz. Some of the most storied sections of San Francisco — including parts of the Financial District as well as the Ferry Building, Fisherman’s Wharf, the Palace of Fine Arts, Chase Center, Oracle Park and Treasure Island — could see flooding from a major tsunami.
The same is true for much of Alameda; sizable chunks of Oakland, Berkeley, Richmond and Marin County; and some areas in and near Silicon Valley, including northern sections of Redwood City and Burlingame.
To the south, some coastal communities along Highway 1 in San Mateo County are in a tsunami hazard zone — such as parts of Pacifica and Half Moon Bay — as are other popular tourist destinations in counties farther south, like Capitola and Monterey.
The risk extends north too. Humboldt and Del Norte counties have significant tsunami risk. There are vast areas around Eureka, next to Humboldt Bay, where there are long, skinny peninsulas that could make an evacuation challenging.
In Ventura County, parts of Ventura, Oxnard and Port Hueneme are in the tsunami hazard area, including the neighborhoods of Oxnard Shores and Ventura Keys, as well as the Ventura Marina Mobile Home Park.
Given the extent of the assessed hazard areas, large-scale evacuations could be ordered, and warranted, in situations with limited time and information.
That was the case in December. Although that warning was later canceled, and no major tsunami developed, Snider said it’s still a good reminder that this kind of disaster can happen, and people need to be prepared.
There was, technically, a tsunami — albeit one measured at a scant 5 centimeters — in Arena Cove off Mendocino County.
A nightmare scenario for California would be a tsunami generated from an underwater quake that occurs close to shore. A particularly chilling prospect for Northern California, as well as Oregon and Washington, would be a magnitude 9 earthquake along the Cascadia subduction zone off the coast.
A major quake in this area could bring a tsunami to San Francisco in as little as an hour. An even closer rupture, such as along the Point Reyes thrust fault, could result in a tsunami hitting the city in as little as 10 minutes, according to city documents.
“You just experienced a significant alert — one that may never happen again to you,” Snider said. “But in the event that it does … ask yourselves, did I have alerts when I needed them?”
It’s important to remember that tsunamis are not like typical ocean waves. They are series of waves that reach shore almost like a turbulent wall of water or a fast-rising flood.
Perhaps nowhere in California better demonstrates the risk tsunamis present than Crescent City. Most notably, the 1964 Alaska earthquake set off a catastrophic tsunami that devastated the city, washing away 29 blocks and killing at least 11 people. Surges reached 21 feet above the average low tide.
A hypothetical magnitude-9.3 earthquake near Alaska’s eastern Aleutian Islands could bring a damaging tsunami to the San Francisco Bay Area in about five hours, and to L.A. and Orange counties in about six.
If you’re uphill or inland from the mapped hazard zones, you should be safe from tsunami. But those who live, work or recreate in a hazard zone should have an evacuation plan, especially since authorities may only have minutes to decide whether to order everyone to higher ground.
If you don’t have prior knowledge of whether you’re in a tsunami hazard zone, and no maps or evacuation signs are available, aim for spots 100 feet above sea level and as far as two miles away from the shoreline, if possible, officials say.
Officials say it’s also important to know if you’re not in a tsunami hazard zone, to avoid complicating evacuations for those who need to move. There’s no need, for instance, to flee San Francisco when much of the city is in a safe zone — just walking a few blocks inland may be all that’s needed.
If evacuation is impossible, your last resort could be going to the third or higher floor of a sturdy building, or even climbing a tree.
And evacuating the Santa Monica Pier doesn’t mean you need to head to the top of Mt. Baldy. Just getting above the nearby bluffs would be enough.
But even where tsunami hazard zones are relatively narrow, many Californians may not have the instinct to get to higher ground after the ground shakes.
And the risk can vary. The tsunami hazard area in Manhattan Beach is essentially limited to the beach and pier on the coastal side of the Strand, the walking-and-biking path that separates the sand from luxury homes. Yet in Hermosa Beach, the latest expanded tsunami hazard area also now covers the pricey homes a block or so east of the trail.
Visiting SeaWorld in San Diego? The theme park is outside the hazard zone, but some hotels and resorts to the west and north are not.
Those who were ordered to leave during the widespread warning in December should assess whether their evacuation plan worked and if there is anything that needs to be tweaked or ironed out, Snider said.
