New tsunami hazard maps highlight threat facing seven California counties — even Napa

Melissa Hernandez
·3 min read
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December 23rd, 2009, San Diego, California, USA. City of San Diego utility worker 2 instals a Tsunami evacuation route sign at the corner of Spray Street and Brighton Avenue on Wednesday morning in the Ocean Beach neighborhood of San Diego, California. The city of San Diego is spending more than $20,000 to put signs in coastal communities as part of an effort to get certified as Tsunami Ready by the National Weather Service. _Mandatory Credit: photo by Eduardo Contreras/San Diego Union-Tribune/Zuma Press. copyright 2009 San Diego Union-Tribune
Tsunami evacuation route sign at the corner of Spray Street and Brighton Avenue in the Ocean Beach neighborhood of San Diego. Tsunami hazard area maps for San Diego and six other counties have been released by the California Geological Survey. (Eduardo Contreras/San Diego Union Tribune)

For the first time since 2009, the California Geological Survey has released new tsunami hazard area maps for Ventura, San Diego, Marin, Napa, Santa Cruz, Solano and Sonoma counties to help residents better understand the risks from a tsunami and how to best plan for a potential evacuation.

In a news release, the state geological agency said the updated maps for the seven counties included new data and improved computer modeling since an earlier series of maps was published 13 years ago, as well as threats from tsunamis originating far away and locally. Thirteen other counties, including Los Angeles and Orange, received new updates over the last year, according to the agency.

"The good news is we haven't seen full-scale large changes on the maps," said Rick Wilson, senior engineering geologist and head of the California Geological Survey's tsunami unit. "It's just a good opportunity for people to go our website and check out if their area has changed, and plan appropriately."

Although tsunamis in California are rare, the state's entire coastline is vulnerable to one at any given time, according to the California Governor's Office of Emergency Services. The last tsunami to hit California was in January, after a volcanic eruption in the South Pacific Ocean near Tonga sent 2-foot tsunami waves barreling through the Bay Area more than 5,000 miles away.

One example of the new modeling predictions shows that an earthquake off the Aleutian Islands, a cluster of islands off the coast of Alaska, could bring 18- to 25-foot swells of waves to the Santa Cruz Boardwalk — twice as high as the predictions made in 2009.

According to the National Weather Service, tsunamis can travel up various bodies of water, including rivers and streams that lead to oceans, meaning they can pick up more momentum for flooding and travel further inland than normal waves and cause more destruction. The most dangerous places to be when tsunamis hit are beaches, lagoons, bays, estuaries, tidal flats and river mouths.

Given that 26.3 million Californians live in coastal parts of the state, it's important that residents are aware of where their tsunami evacuation zones are, and how they plan to get there in the event a tsunami hits the area.

Despite the changes to these new maps, the probability of these events is low, Wilson said, and the purpose of the new maps is to help Californians be best prepared in the rare event that a tsunamic event does occur.

"Our goal is to ensure that coastal communities are aware of and prepared for the next tsunami," the California Geological Survey said. "The updated Tsunami Hazard Area Maps can be used by officials, communities and individuals/families to update or create their tsunami evacuation plans."

This story originally appeared in Los Angeles Times.