Downtown SF, North Shore is included in the new Bay Area tsunami danger zones

[ad_1]

If a tsunami hit once in a millennium, the waves could inundate the waterfront more than scientists previously feared. While alarming, new tsunami hazard maps created by the California Geological Survey are meant to show how people know if they are in a vulnerable area and how to get to safety – often just walking a few blocks away.

On Thursday, the California Geological Survey released new tsunami risk maps for San Francisco, Contra Costa and Santa Clara counties, along with several counties in Southern California, for the first time since 2009. They’re updated with new technology and knowledge gained from major events like the disaster in Japan. 2011 Tohoku earthquake and tsunami, interactive maps show more flood risks in downtown San Francisco, the Marina and North Beach neighborhoods, and areas around the Port of Richmond than previously expected.

The danger zones reflect the worst-case scenario: a tsunami triggered by a 9.3-magnitude earthquake in the eastern Aleutian Islands off Alaska, the site of greatest danger for such devastating waves hitting central California. Such an event would be extremely rare — and it would take five hours to reach the Bay Area, so there would be time to warn people to get to safety, said Rick Wilson, chief engineering geologist for the California Geological Survey, part of the State Department. from conservation.

“So we won’t see a tsunami 99% of the time,” said Wilson, a member of the map update team. “But it is good to prepare for the worst and hope for the best.”

In March, the state released updated tsunami risk maps for San Mateo and Alameda counties, and will do the same for the rest of the Bay Area and the state by early next year.

Video: Carlos Avila Gonzalez The Chronicle

If an earthquake occurs that could trigger a tsunami, the National Tsunami Warning Center provides alerts, as do local governments, with everything from loudspeakers to Amber Alert-style text messages indicating if an evacuation was warranted. There are different levels of risk – while a tsunami warning warns people to stay away from beaches and ports, a tsunami warning prompts internal evacuation.

The maps from the California Geological Survey are meant to warn people in advance if they are in a tsunami danger zone and how far they will need to get to safety.

“You don’t have to run into the mountains to be safe,” Wilson said.

This time, Wilson and his colleagues used lidar mapping technology, which has a higher resolution than previously used, and has identified low-lying areas most vulnerable to flooding.

It includes parts of downtown San Francisco, where the danger zone now extends inland as far as Fremont Street in the South Off Market District and Sansom Street in the Financial District. In North Shore, the area has been extended from Beach Street as far south as Chestnut in Columbus. In Ocean Beach, the San Francisco Zoo is preparing a new tsunami evacuation area, which led to the sighting of Noah’s Ark.

In a worst-case tsunami scenario, Wilson said, waves could be as high as 30 feet at the coast and 10 to 15 feet into the bay. If such a tsunami hits the San Francisco waterfront, for example, the water could be above the bay’s edge and dissipate to about two feet at the outer reaches of the danger zone, enough to bring people down, he said.

However, Wilson said that any work being done to protect the coast from sea-level rise could also help protect it from a tsunami. Plans underway in San Francisco to modernize the $3 billion Embarcadero seawall will help prepare for sea-level rise and tsunami risks, said Adrian Becelli, deputy director of the San Francisco Emergency Management.

“This is a great example of where capital investment has many benefits for all the different risks and risks,” she said.

Picelli said city departments, from transit to public works, are conducting drills to prepare for events like a major tsunami. In addition, her division is working with the Department of Recreation and Parks on a worst-case evacuation plan for the zoo.

The National Tsunami Warning Center provides alerts: tsunami.gov

California Tsunami Preparedness Guide. Tsunami Hazard Maps: www.tsunami.ca.go

For emergency alerts, text your zip code to 888-777

see more folded

In Contra Costa County, previous maps of the Port of Richmond showed that tsunami risk was mostly in the port itself and its adjacent harbor, while new maps of the evacuation zone extend north of Interstate 580. In Santa Clara County, flooding risks are low because a large tsunami will dissipate into the area, Wilson said. About two feet by the time he reaches the South Bay, existing levees and ponds will protect residential and commercial areas.

Updated maps of Alameda County, released in March, show wider danger zones in West Berkeley, extending as far east as Sixth Street. In Auckland, new areas include Lake Merritt and a small area east of Bay Bridge.

A tsunami can strike the California coast from many sources, both near and far. An earthquake near Point Reyes may cause a small local tsunami, and the 2011 Japan Tsunami killed one person in California and caused $100 million in damage to the state’s ports and harbors. But a major earthquake in the Aleutian Islands poses the greatest risk because the fault is in the subduction zone – the kind most likely to cause a tsunami – and the resulting waves will go straight into central California.

In 1964, a 9.2-magnitude earthquake in a part of nearby Alaska triggered a 21-foot tsunami that killed 12 people and wreaked havoc in Crescent City (Humboldt County). The 2011 Japan earthquake and tsunami, which killed nearly 20,000 people, was a 9-magnitude earthquake in a subduction zone just 80 miles east of Japan. The tsunami only took 20 to 30 minutes to make landfall, while California has a much longer warning.

“We want people to see that this is a risk,” Wilson said. “But we want them to have hope that there are things they can do to take care of the business.”

Tara Duggan is a staff writer for the San Francisco Chronicle. Email: [email protected] Twitter: taraduggan

The National Tsunami Warning Center provides alerts: tsunami.gov

California Tsunami Preparedness Guide. Tsunami Hazard Maps: www.tsunami.ca.go

For emergency alerts, text your zip code to 888-777

[ad_2]