Preparing for the ‘Big One’

Courtesy San Francisco Public Press/J.K. Nakata

Twenty-nine years ago this week, the San Andreas Fault sent a shock that reverberated throughout the Bay Area. This shock was responsible for 63 deaths, over 3,700 injuries, and $6 billion in damages. Perhaps the most jarring numbers from the 1989 tremor were the ones revealing that it was not a major earthquake. With a magnitude of 6.9 and an epicenter 60 miles away from San Francisco, the Loma Prieta earthquake was not the “Big One.”

In fact, since 1906 the Bay Area has enjoyed a historically quiet period of seismic activity. This quiet period seems to be coming to an end. The United States Geological Survey estimates there is a 72 percent chance of a major earthquake happening in the next 25 years. This anniversary of Loma Prieta should serve as an important reminder for San Francisco residents: we know the “Big One” is coming and we must prepare.

One of the most important actions we can take as a city to prepare for a major earthquake is to strengthen our Embarcadero Seawall. The Seawall is a three-mile long rock and concrete wall along San Francisco’s northeastern waterfront that is over 100 years old. A remarkable engineering feat in the early 1900’s, the Seawall was built in the heart of earthquake country without today’s seismic resistant design and engineering. It was also built over “young bay mud,” a soft, weak mud that makes for a poor foundation and can amplify earthquake shaking.

The Embarcadero Seawall supports over 50 emergency response and recovery assets including Fire Station 35, which houses the fireboat fleet. After an earthquake, the Embarcadero will be used by first responders to help evacuate people from downtown and bring in supplies to the City. It will be difficult for first responders to help those in need if the Embarcadero Seawall fails.

The Embarcadero Seawall is the foundation for all ferry landings and waterfront piers and docks.

The City estimates that up to 250,000 people will need to evacuate San Francisco by water in an emergency. Ferry service is key to their evacuation, especially if an earthquake closes bridges, highways, and BART. Ferry landings and boat docks along the waterfront will also provide landing areas for disaster service workers and emergency equipment and supplies. In an emergency, it is critical that our Embarcadero Seawall remains stable.

The 6.9 magnitude Loma Prieta earthquake cracked concrete bulkheads along the Embarcadero and caused cracking near Market and Mission Streets, among other damage across San Francisco and the Bay Area. However, because the epicenter was 60 miles away, shaking was too moderate and too short to trigger widespread liquefaction and lateral spreading of the Embarcadero Seawall. A similar earthquake located much closer on one of the nearby faults will cause much higher ground shaking and damage.

For a clearer picture of what may happen to the Embarcadero Seawall in an earthquake, you can check out an earthquake simulation video on the Port’s YouTube channel.

Understanding this risk, the City of San Francisco, acting through the Port of San Francisco, has begun a multi-billion-dollar effort to strengthen our Embarcadero Seawall. Phase I of the Seawall Program is addressing the most critical emergency response and life-safety upgrades to the Seawall. You can learn more about the Seawall Program at sfseawall.com.

The City is working to proactively prepare for the next “Big One” because we know that a large earthquake – one much larger than Loma Prieta – is likely to hit the region in the next 25 years.

The only thing we don’t know is when. On the 10 th Annivesary of the Great ShakeOut and year round, together we can prepare and protect the City that we all love.

For a clearer picture of what may happen to the Embarcadero Seawall in an earthquake, you can check out an earthquake simulation video on the Port’s YouTube channel:

Mary Ellen Carroll is the Executive Director of the Department of Emergency Management and oversees 241 employees who are responsible for leading San Francisco in planning preparedness, communications, response and recovery for daily emergencies, large-scale City wide events and major disasters.

City Administrator Naomi M. Kelly oversees 25 City departments and divisions including Public Works and Real Estate and chairs the Capital Planning Committee, which develops the City’s 10-Year Capital Plan.

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