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Would SunCal’s Buildings Hold Up in a Strong Earthquake?

SunCal’s hired-gun planning guru Peter Calthorpe likes to reference San Francisco’s Marina District when describing his vision for mid-rise mixed-use buildings at Alameda Point. But would those soft-story buildings hold up when subjected to a strong earthquake along the Hayward fault?

As reported in the San Francisco Chronicle last week, a recent study by the Community Action Plan for Seismic Safety says that San Francisco’s soft-story buildings are at significant risk in the event of a 6.9 magnitude (Loma Prieta) to 7.9 (1906 quake) magnitude earthquake. “Soft-story” structures are prevalent in San Francisco and they typically house a store or restaurant on the first floor, and apartments above. Such structures are called “soft-story” buildings because of the open spaces in the wall on the ground-floor – a window or garage door – where there might otherwise be a solid wall with vertical studs or columns and sheetrock or plywood to provide stability. According to the SF Chronicle report “Earthquake experts said the study demonstrated that soft-story structures represent a tremendous risk to the city.” Many such soft-story buildings in the Marina district of San Francisco were damaged and 35 were completely destroyed in the 6.9 magnitude 1989 Loma Prieta earthquake. Like the Marina District, land at Alameda Point consists largely of fill and is subject to liquefaction. 63 people were killed in the Bay Area during the Loma Prieta event.

Alameda Point Highly Susceptible to Liquefaction During an Earthquake

Alameda Point Highly Susceptible to Liquefaction During an Earthquake

Granted, the San Francisco study focused on existing wood-frame soft-story buildings in San Francisco, and we presume – we hope! – that new construction at Alameda Point would use steel columns, shear bracing and other modern construction methods to make the structures safe. But earthquake shaking maps from the Association of Bay Area Governments show that Alameda Point would be subjected to “Violent” shaking (IX on the Mercalli scale) under a 6.7 magnitude earthquake along the South Hayward fault. During the Loma Prieta earthquake, the Marina District was subjected to “Very Strong” shaking resulting from a quake whose epicenter was 50 miles south. A magnitude 6.5 quake along the North Hayward fault would also produce “Violent” shaking at Alameda Point.

Alameda Shake Map for 6.7 Magnitude Earthquake on South Hayward Fault

Alameda Shake Map for 6.7 Magnitude Earthquake on South Hayward Fault

In March of this year, the U.S. Geological Survey released a report that said “An earthquake of [magnitude] 6.8 or greater on the Hayward Fault, in the heart of the San Francisco Bay area, is increasingly likely.” It seems quite likely that the future residents of Alameda Point will have to contend with a substantial earthquake, although we could get “lucky” and suffer such an earthquake in the intervening years before construction at Alameda Point begins.

SunCal’s draft development concept document for Alameda Point says very little about the seismic risks there. Only one page of the 134 page document speaks to the seismic issues at Alameda Point and even then, SunCal asserts only that “The seismic hazard posed by liquefaction is rectifiable.” and while they mention possible mitigation strategies – pile foundations, cement injection etc. – they provide no specifics as to which techniques they plan to use for which sites or which uses, (residential, mixed-use, commercial), and they leave the question open to “further analysis.”

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