Tsunami inundation map
New inundation maps show an increased risk for parts of Half Moon Bay due to tsunami. The yellow region represents the area that could flood in a worst-case scenario. Illustration courtesy tsunami.ca.gov

New maps released this month reveal heightened tsunami risk to coastal neighborhoods from Pescadero to Pacifica. The maps, last updated in 2009, use new data and computer modeling to show a worst-case scenario — a magnitude 9.3 earthquake in the eastern Aleutian Islands off Alaska.

In Half Moon Bay, the most significant update to the maps is just north of downtown, where experts predict that strong waves could cross Highway 1 and put the entire Arroyo Leon watershed at risk, as well as the communities around Terrace Avenue, Grandview Boulevard and Spindrift Way. Farther north, lower El Granada, Moss Beach and the entire Princeton areas are at risk. Down south, overflowing San Greogrio, Pescadero and Pomponio creeks all could threaten South Coast communities.

There is precedent for tsunamis on the Coastside, but the area has so far emerged relatively unscathed. In 1963, an earthquake in Alaska prompted thousands of Coastsiders to evacuate, and in 1964, the most destructive tsunami in the state on record killed 12 people in Crescent City. A 2011 quake in Japan caused $100 million in damage to state ports and harbors. In each of the incidents, the Coastside remained largely untouched.

Last week, Pacifica Community Emergency Response Team presented a 90-minute educational course via Zoom to make sure residents are signed up to receive alerts from local authorities should a tsunami threat occur. The advice from authorities to those in high-risk zones is to move inland as soon as it’s safe and not return until officials give the all-clear.

The California Geological Survey, which created the new maps, estimates a five-hour window between an Alaska earthquake and the first surges to the San Mateo County coastline.

"That may seem like a lot of time, but it will take an hour or so for the National Tsunami Warning Center to issue a warning to California and then additional time for local authorities to determine whether an evacuation is necessary," wrote Rick Wilson, head of the CGS Tsunami Program in a press release. "The bottom line is, if you’re near the coast and feel strong shaking from a local earthquake or get an official notification to evacuate, move inland as soon as possible.”

In Pacifica, the maps show the Pedro Point and Linda Mar shopping centers and Rockaway Beach Plaza well within the tsunami evacuation zone. The same is true for the Linda Mar

neighborhood all the way to Cabrillo School, plus beachside parts of the Shelter Cove neighborhood. Most of the western part of the Fairway Park neighborhood is in the tsunami evacuation zone as is Mori Point and the Quarry.

In Sharp Park, everything between Fifth Avenue and Santa Maria Avenue along Palmetto Avenue could be affected, including City Hall all the way to Francisco Boulevard and across Highway 1. Cedar Lane, Sharp Park Golf Course and Eureka Square are all in the affected area. The Sharp Park and Manor neighborhood beach areas are affected.

Jessica Blair, communications director for the city of Half Moon Bay, said staff is reviewing the new maps and will integrate them into emergency planning. San Mateo County is also currently updating its Local Hazard Mitigation Plan, last updated in 2016, to prepare for disaster and response in coordination with the Federal Emergency Management Agency. But the new maps aren’t just important to emergency preparedness, they also dictate local building codes and insurance coverage.

Farmers Insurance Group agent Leonard Stone said insuring a home in a tsunami risk zone is cheaper than in a flood zone. He said homeowners can purchase standard flood insurance at a preferred rate due to the tsunami risk.

“I’ve been here since 1999 and I’ve never seen a tsunami,” Stone said. “In order for it to be considered a worse hazard, you can’t have a wave hit one house. It must be a minimum of five houses or a quarter mile of frontage.”

Stone said homeowners are given a deductible and deal with FEMA, which manages the national flood insurance program and dictates rates for each county and even down to the address. For areas susceptible to flooding, like much of Linda Mar in Pacifica, the premium is higher.

“We’ve had flood claims, but very minimal,” Stone said. “The Army Corps of Engineers and the city did work to bring the area out of the flood zone, but the lender looks at the lowest point. Some of them own to the middle of the creek.”

Ron Wilson of Omni Insurance Agency said in the 45 years he has been in business, he has heard only two questions from residential and commercial clients about tsunamis. So far, Wilson said he hasn’t received any calls from clients in the area who are looking to upgrade.

“We don’t need (tsunami coverage) in most areas of town,” Wilson said. “… Pacifica has been a safe zone.”

Recommended for you

Load comments