These California coastal cities face increasing flood risk from the tsunami, data shows

The risk of damaging floods from major tsunamis may be greater than many people realized along California’s famous coastline range, state officials say it will further strengthen the need to take notes when residents live or visit dangerous areas.

The latest risk assessment, published by the California Geological Survey and outlined in a map reviewed by the Los Angeles Times, illustrates the devastation that can arise from scenarios that are considered extreme but realistic. For example, a large tsunami could infiltrate Marina del Rey, Long Beach and nearby bands of dual-port complexes at elevations up to 15 feet above sea level.

The worst tsunami could flood a significant area of ​​Oakland, Berkeley and Alameda up to 18 feet above sea level.

Floods can reach up to 30 feet above average high tide along the open seas of Humboldt Bay and Eureka area, and up to 50 feet towards Crescent City and Cayukos.

However, for most Californians, the exact extent of tsunami risk is less important than knowing that these hazard zones exist in the first place. The magnitude 7 Quake on December 5th was a pivotal reminder of this, prompting a tsunami warning affecting millions of people in Northern California.

If a significant tsunami occurs, it can only make a difference for just a few minutes. Along California’s north coast, some people only take 10 minutes to reach the evacuation area after a major offshore earthquake.

“It’s rare for tsunamis to be damaged in California, but they do happen. You either live on the coast or be aware of this potential danger,” said Steve Bollen, head of the California Geological Survey, when the updated Tsunami Hazard Area Map was released.

To find out if you live in a tsunami hazard zone, go to conservation.ca.gov/cgs/tsunami/maps.

The latest maps were released between 2020 and 2022. Although it was avoided from the spotlight by other news events during that period, it nevertheless includes some major updates from previous tsunami flooding maps released over a decade ago.

And with the state’s annual tsunami preparation week scheduled to begin on Saturday, officials say it’s important for residents to get used to the risks of their local people.

Updates to California’s tsunami hazard region followed Japan’s catastrophic tsunami in 2011.

Before that disaster, Japan relied on data from hundreds of years of records to estimate the risk of a tsunami, which Boren once “was completely reasonable.” However, the disaster demonstrated the need for scientists to consider even rarer events. It could only attack once every 1,000 years or so.

As a result, California has chosen to adopt a “very conservative approach” in its maps, “hoping to avoid the tragic loss of life experienced in Japan,” Boren said in a previous statement.

There are several scenarios where California can get a lead time of several hours than it would cause tsunami damage. However, if the trembling approaches the shore, there is little or no warning except for the shaking itself.

“The bottom row is when you move inland as quickly as possible near the coast, receiving official notifications to shake or evacuate from a local earthquake,” said Rick Wilson, a senior engineering geologist at the California Geological Survey and Tsunami Division, in a 2021 statement.

The latest update on the map has expanded the potential tsunami flood area along Ocean Boulevard and Belmont Shore to parts of Long Beach, including Malibu, Santa Monica, Venice, Marina del Rey, Hermosa Beach, Redondo Beach and San Pedro.

Areas of prominent interest in Los Angeles County include Long Beach and the ports of Los Angeles and Marina del Rey around Aramitos Bay, as there are few evacuation routes, according to the California Geological Survey.

Whenever possible in extreme scenarios, flooding would “invade almost all of the land in the port and surrounding communities,” Wilson said when the latest map was released.

In updating the map, San Francisco also saw a “significant increase in mapped tsunami hazards” in the financial district at the foot of Market Street and part of North Beach, south of Embarcadero. The zones include Embarcaderobert and MuniStation and the Embarcadero Centre.

“Both these are areas with very low land elevations that could be affected by a slight increase in waterfront flooding,” the geological survey said.

In many places, changes to the hazard map were relatively modest. Some, like Newport Beach, were expanded to add small buffers to roads and landmarks beyond modeled flood areas to help local officials communicate evacuation plans.

“There’s a place on the West Coast of the US, and here in Alaska, there’s a safe evacuation for events that are almost on the shore… there’s a much lower success rate,” said Dave Snyder, tsunami warning coordinator at Alaska’s National Tsunami Warning Center. “That’s the primary reason why people need to understand what their hazard zone is doing in advance.”

The changes went in both directions. Some areas, such as the Huntington Beach and the Bolsatica area, saw tsunami-risk areas shrink after new analysis showed that levees and ponds would help better protect the public than originally thought.

What became clear after extensive warnings in December was that many Californians had no idea where the tsunami warning zone was.

And, as the map shows, it is not always immediately exposed along the coast. Tsunami Hazard Zones can be extended to Bayside and riverside areas relatively far from the Pacific coast, which represents the largest flood area in many scenarios, according to the California Geological Survey.

California’s tsunami-risk areas are vast in some areas, including some of the state’s most expensive properties and most famous destinations. Sunset Beach, Seal Beach, San Diego and nearby Coronado.

There are also popular tourist hotspots, from Malibu to Santa Barbara’s waterfront, the Monterey Bay Aquarium and the Swiss of Santa Cruz. Some of San Francisco’s most renowned sections can be seen in parts of the financial district and floods from the large tsunami, including Ferryville, Fisherman’s Wharf, Fine Arts Palace, Chase Center, Oracle Park and Treasure Island.

The same can be said for many of Alameda. A considerable chunk of Oakland, Berkeley, Richmond and Marine counties. Several areas near Silicon Valley, including Redwood City and Northern Burlingame.

In the south, several coastal communities along Highway 1 in San Mateo County are located in tsunami hazard zones, such as Pacifica and parts of Half Moon Bay.

The risks are also spreading north. There is a risk of tsunamis in Humboldt and Del Norte counties. There is a vast area around Eureka, next to Humboldt Bay. There is a long, narrow peninsula that can make evacuation difficult.

In Ventura County, parts of Ventura, Oxnard and Port Fu Enmeme are located in the tsunami hazard area, including the Ventura Marina Mobile Home Park, near the Oxnard Shores and the Ventura Keys.

Given the range of hazard areas assessed, large evacuations could be ordered and guaranteed in situations with limited time and information.

That was the case in December. That warning was later cancelled and there was no major tsunami, but Snyder said it still makes a good memory that this type of disaster could occur and that people need to prepare.

Technically, Mendocino County’s Arena Cove had a tsunami, measured at just 5 centimeters.

The California nightmare scenario is a tsunami produced by an underwater earthquake that occurs near the coast. Like Oregon and Washington, Northern California’s particularly cold outlook would be a magnitude nine earthquake along the Cascadia subduction zone off the coast.

The area’s major tremors could take the tsunami to San Francisco in just an hour. City documents show that a rupture closer along the point where Reyes stabs the fault could hit the city in just 10 minutes.

“You just went through an important alert, and it may not happen to you again,” Snyder said. “But if that’s what you do… asked yourself and did you get an alert when you needed it?”

It is important to remember that tsunamis are not like typical ocean waves. They are a series of waves that reach the coast like turbulent walls and rapid rising floods.

Perhaps nowhere in California is better demonstrating the risk of a tsunami as in Crescent City. Most notably, the 1964 Alaska earthquake devastated the city, washing away 29 blocks and causing a devastating tsunami that killed at least 11 people. The surge reached 21 feet above average low tide.

The hypothetical magnitude-9.3 earthquake near the eastern Aleutian Islands of Alaska could lead to a tsunami that would damage the San Francisco Gulf region in about five hours, and the counties of LA and Orange in about six people.

If you are uphill or inland from a mapped hazard zone, you must be safe from the tsunami. However, those living, working or recreating in hazard zones should develop evacuation plans, especially as authorities only have a few minutes to decide whether to order everyone to the highlands.

If you don’t have any prior knowledge about whether you’re in the tsunami hazard zone and you don’t have maps or evacuation signs available, you’re aiming for a spot 100 feet above sea level.

Officials say it’s also important to know if you’re not in the tsunami hazard zone. For example, you don’t have to escape from San Francisco when many of the cities are in safe zones. Just walk a few blocks inland and you need everything.

If evacuation is not possible, your last resort can either go to the three or more floors of a sturdy building or even climb a tree.

And evacuating the Santa Monica pier does not mean you need to head to the top of Mount Bardi. It’s enough to just get to the nearby bluff.

However, even when the tsunami hazard zone is relatively narrow, many Californians may not have the instinct to reach the highlands after the ground shaking.

And the risks may vary. The tsunami hazard area of ​​Manhattan Beach is essentially confined to the beaches and piers on the shoreside of the chain. But Hermosa Beach also has the latest expanded tsunami hazard area covering expensive homes east of the trail.

Would you like to visit Sea World in San Diego? The theme parks are outside the hazard zone, but not in some hotels and resorts west and north.

Those ordered to leave during the widespread warning in December should assess whether the evacuation plan worked and whether there are any items that need to be adjusted or ironed, Snyder said.

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