The California Geological Survey has released new tsunami hazard maps for the counties of San Francisco, Santa Clara, and Contra Costa, which have now been updated to take a worst-case scenario into account.
The 2021 maps, produced by the CGS in collaboration with the California Governor’s Office of Emergency Services, replace the 2009 versions with new estimates that cover larger areas that may need to be evacuated in the event of a tsunami.
Steve Bohlen, Acting State Geologist of California and head of the CGS, said the heightened level of preparedness was inspired by the 2011 Tohoku-Oki earthquake and tsunami.
“Japan used data from hundreds of years of tsunami records in its planning, which seemed perfectly reasonable,” Bohlen said in a statement. “Then it was hit by a millennium tsunami.”
The “worst case scenario” of the CGS for the Bay Area would be a 9.3 magnitude earthquake in the Aleutian Islands off the west coast of Alaska. A tsunami caused by such an earthquake would reach the Bay Area within five hours, leaving little time for an evacuation warning and safe evacuation of the residents.
In 1964, a 9.2 magnitude earthquake in Alaska caused a tsunami that reached Crescent City in four hours, killing 12 people and devastating much of the city’s business district.
Using the Aleutian scenario and other sources, the CGS developed new tsunami hazard maps to inform local residents and emergency planners which areas may need to be evacuated and how far inland to move.
The most significant increase in the tsunami-prone area is low-altitude land in San Francisco’s North Beach and downtown Market Street, as well as residential and commercial areas around the Port of Richmond, according to CGS.
The new maps will help educate the state hazard reduction plan so state agencies, local and tribal governments can prepare for potential tsunamis. The maps can also help inform the response to climate change, the CGS said, as the same low areas that are prone to flooding during a tsunami are also prone to flooding from rising sea levels.
A total of thirteen new maps were released by the CGS in 2021, and it is hoping to publish maps for the remaining seven California counties next year.