California Geological Survey Releases New Tsunami Hazard Maps for Local Areas | Local News

Posted on July 9, 2021
| 5:51 p.m.

The California Geological Survey (CGS) has released new interactive tsunami risk zone maps for Santa Barbara and San Luis Obispo counties, useful for evacuation planning during an extraordinary event.

Maps allow users to enter an address to determine if a particular property is in a tsunami risk area. Local tsunami evacuation material will be added to the online mapping interface as it is developed. To view the maps, visit https://www.conservation.ca.gov/cgs/Pages/Tsunami/TsunamiHome.aspx.

In conjunction with the California Governor’s Office of Emergency Services (Cal OES), maps of the tsunami risk area include new data and improved computer modeling results, and replace maps released by CGS in 2009.

The new maps aren’t just based on how far a worst-case rise in seawater could go, they also include minor interior “buffers” at roads and landmarks to clarify where people need to go. evacuate to be safe. Buffer zones also take into account potential errors and uncertainties in the modeling.

The maps incorporate the hard lessons Japan learned a decade ago from the Tohoku-Oki earthquake and tsunami, said Steve Bohlen, acting California state geologist and head of CGS.

“Japan used data from several hundred years of tsunami records in its planning, which seemed perfectly reasonable,” Bohlen said. “Then he was hit by a millennial tsunami. So we take a very conservative approach and use a thousand year scenario as a benchmark for our new maps, hoping to avoid the tragic loss of life in Japan.

“Although destructive tsunamis are rare in California, they have [happened] and happen. If you live or visit the coast, you should be aware of this potential danger. “

While the new maps for the two counties take into account a variety of potential tsunami sources, the worst-case scenario was modeled from a 9.3-magnitude earthquake in the eastern Aleutian Islands. Examples of new information provided by these cards:

Santa Barbara County

The Santa Barbara airport area has seen both modest increases and decreases in tsunami risk. Most of the areas that have experienced increased risk are low lying and undeveloped areas such as canals or wetlands. The east-west runway at the airport saw a decrease in the risk of a tsunami.

Tsunami risk increased moderately in the Santa Barbara and Carpinteria regions based on a better understanding of tsunami sources and new modeling results.
For most other parts of the county, the risk of a tsunami remains the same.

San Luis Obispo County

The largest increases in tsunami risk occur at Cayucos, where the highest climb altitude has increased from around 30 feet to around 50 feet in a few places. The entire area east of the pier and the ocean side of South Ocean Avenue may be at risk from extreme events.

There is a slight increase in tsunami risk at Los Osos, San Simeon and the northern part of Morro Bay near Highway 1. For the southern part of the county, the tsunami risk remains the same or – at Avila Beach and Oceano – is slightly reduced.

Under the Large Aleutian Islands scenario used by CGS, the first surges would reach the counties in five to six hours. “This time will pass quickly, as scientists and emergency planners at the federal, state and local levels will all need to assess the threat level before issuing an evacuation warning,” said Rick Wilson, CGS Tsunami program manager. .

“Summary: If you are near the coast and experience strong shaking from a local earthquake or receive an official notification to evacuate, move inland or at a higher altitude. high as soon as possible, ”he said. “A large tsunami wave can be fascinating to watch, but you don’t want to get close to it. ”

The maps inform the state’s risk mitigation plan and contingency planning efforts so that state agencies, local governments, tribal governments and others can effectively mitigate and respond to emergencies that may arise. in their areas of responsibility.

“We appreciate working with the Department of Conservation’s California Geological Survey to provide Californians living, working, or visiting a tsunami-prone area with the tools they need to develop evacuation plans for themselves, their families. families and their businesses, ”said Lori Nezhura, deputy director of planning, preparedness and prevention, Cal OES.

Over 150 tsunamis have hit California shores since 1800. Most were barely noticeable, but a few have caused death or significant damage. The 2011 tsunami that devastated Japan also caused $ 100 million in damage to ports and ports in California, including unsafe conditions and minor to moderate damage to a number of southern California ports.

The most destructive tsunami to hit California occurred on March 28, 1964. Several waves up to 21 feet high swept through Crescent City four hours after a 9.2 magnitude earthquake in Alaska, killing 12 people and leveling much of the city’s business district.

CGS, which is part of the California Department of Conservation, has released maps of tsunami risk areas in 13 counties and hopes to update the maps for the remaining seven coastal counties within the next year.

“Managing the risk of geological events such as tsunamis, as well as mining and oil production is one of the pillars or cornerstones of our department,” said Bohlen.


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