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Tsunamis pose risks across California coasts. But should one major strike be done, how bad is it?
A single tsunami may not cause the worst-case scenario in all regions. However, in total, over 680,000 Californians are in areas with tsunami-risk during the day. And overall, $12.6 billion in damages is possible in California’s 20 coastal and Bayside counties. This does not include damage to ports, ports, roads, essential facilities or other infrastructure.
There are two main types of tsunamis: The first “distant source” tsunami comes from afar, like the one born from the Alaska earthquake. This provides a broad warning that it will be six hours in LA and five hours in San Francisco, but it could create the highest level of flooding for the nation’s massive swath.
After that there is a “nearby sauce” tsunami. This allows you to wash the land 10 minutes after a nearby earthquake. There is very little notification or evacuation time.
Here are some scenarios for different parts of California. Unless otherwise noted, the figures come from the California Tsunami Program run by the California Governor’s Office of Emergency Services and the California Geological Survey.
Southern California
Remote Source Tsunami: Waiting for people to evacuate 30 minutes after an official evacuation warning is given can lead to more than 350 people dead or injured along the Southern California coast. This includes around 200 casualties in Los Angeles County, around 80 in San Diego County, 60 in Orange County and around 12 in Ventura County.
Hypothetical magnitude 9.3 earthquakes from Alaska – similar scale to the intense heartbeat of the 1964 tsunami generation provides a six-hour warning. The enraged masses from Chile could provide a 13-hour warning.
The largest projected remote source tsunami could bring waves 15 feet above average sea level to Marina del Rey, Santa Monica Pier, Naples and the Bay of Aramitos. 14 feet elsewhere in the rest of Long Beach. 10 feet in the ports of Manhattan Beach, San Pedro, Los Angeles and Long Beach. 9 feet in Malibu, Redondo Beach and Palos Verdes Hills. 8 feet at Leocarie Jo State Beach.
These estimates were published by the California Geological Survey and published in the City of Los Angeles Hazard Mitigation Plan.
Estimated damage from remote sources tsunami: over $1.4 billion.
Sources near Tsunami: Los Angeles could see the tsunami travel from its source to the coastal area in 10 or 15 minutes, the city’s tsunami plan warns. According to the public documents, 30 feet of tsunami height can be locally generated in Avalon on Catalina Island, depending on where the ruptured obstacle or the location of the landslide underwater. 24 feet in Palos Verdes Hills. 18 feet in two ports. 11 feet in Redondo Beach. 9 feet in Malibu. 8 feet from Long Beach and Santa Monica Pier. 7 feet in Manhattan Beach and San Pedro. 5 feet from Marina Del Rey. 4 feet at Leocarie Jo State Beach.
In the city of Los Angeles, officials say the most devastating scenarios include underwater landslides caused by earthquakes. “I don’t know there will be landslides until the waves reach them.”
Other LA County areas with considerable vulnerability include Port, San Pedro and Long Beach. The city of Los Angeles has an estimated 23,000 residents in the Tsunami Hazard area. In Long Beach, that number is 31,000.
Central coast
Distant Source Tsunami: Waiting 30 minutes to evacuate after an official warning is given can kill or injured more than 230 people. Santa Cruz County was able to cause more than 130 casualties. San Luis Obispo County, approximately 80. The estimated potential victim toll could be 16 in Monterey County and seven in Santa Barbara County.
Estimated damage from remote sources tsunami: over $3.5 billion.
Nearby Source Tsunami: Santa Cruz and Monterey counties were able to see the tsunami within minutes following the underwater landslide that Quake triggered, documents from both counties say. “Even moderate earthquakes can cause local source tsunamis from submarine mines in Monterey Bay,” the public documents say.
A nearby source tsunami could bring waves up to 15 feet above the average sea level in Marina City and nine feet of the Salinas River. Data published in Monterey County Hazard Mitigation Plan shows that it is 8 feet on the Pajaro River and Sand City northeast of Monterey and 6 feet on Moss Landing.
Such devastation is not unprecedented. According to the US Geological Survey, a major earthquake in the Santa Barbara area in 1812 caused the tsunami, which “cleared many coastal villages and destroyed ships at the port.”
The California Geological Survey reported that seven feet of waves were generated from the 1927 tsunami produced by an earthquake about five miles west of the Santa Barbara County coast.
The USGS said there is evidence of sediment from underwater landslides off the coast of Santa Barbara, dating back 160,000 years.
Bay Area
Distant Source Tsunami: Waiting 30 minutes to evacuate after an official warning is given can kill or get injured over 1,300 people. Of these, about 500 people could be in San Francisco. There are about 300 people in San Mateo and Marine counties. There were 200 people in Alameda County and 33 people in Contra Costa County. Just north of the Mendocino County area, five people could die or get injured in that scenario.
A virtual tsunami-generating earthquake in Alaska could provide a five-hour warning. One from Chile can provide a 13-hour warning.
The largest projected remote source tsunami can result in a tsunami 32 feet above the average sea level of Ocean Beach, San Francisco. 31 feet in Pacifica, San Mateo County. 27 feet in Bolina, Marine County. 18 feet of Alameda. 14 feet in Sausalito and San Francisco’s Aquatic Park. 13 feet on Alcatraz Island. 11 feet in Richmond and Treasure Island, according to the California Geological Survey.
Estimated damage from remote source tsunami: over $6.5 billion.
Near-source Tsunami: Northern California was able to generate a tsunami at 9 feet above sea level in Bolinas. Pacifica 8 feet. 7 feet of Sausalit. 6 feet at Ocean Beach. Alameda 5 feet. 4 feet in Alcatraz Island, Treasure Island, Aquatic Park, Redwood City and Richmond.
North Coast
Cascadia scenario: Given its proximity to the Cascadia subduction zone, Del Norte County, the northernmost coastal region of the state, is probably more at tsunami risk than any other part of California. If people are waiting to evacuate 10 minutes after the earthquake – the shaking itself will be a warning to escape – more than 3,150 people are at risk of being killed or injured by the tsunami in Del Norte County, and more than 720 will be at risk in nearby Humboldt County.
Floods can reach up to 30 feet above average high tide along the open seas of Humboldt Bay and Eureka area, heading up to Crescent City, up to 50 feet.
“The massive tremors produced by the Cascadia subduction zone could create twice the waves that were the 1964 event, especially in the Crescent city,” said Rick Wilson, former head of the California Geological Survey Tsunami Program, in a statement.
Damage estimate: Del Norte County, home to Crescent City, could suffer more than $1 billion in damage. Humboldt County, home to Eureka, was able to see $22 million.
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