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A lot of San Francisco’s inexpensive housing is slated for seismic hazard zones | San Francisco Information

San Francisco’s affordable housing plans are on shaky ground. Quite literally.

In July, Mayor London Breed broke ground on Treasure Island’s second affordable housing project, Star View Court, which will include 138 units upon completion. Yet looming over it is the cloud of a possible natural disaster.

Treasure Island is situated entirely atop a seismic hazard zone. Developed in 1936 with artificial fill, the island is designated as a “liquefaction zone.” In the event of an earthquake, strong shaking could lead the water-saturated soil underneath to give way.

Some 178 affordable housing projects encompassing 20,089 total units, 8,630 of which would be designated affordable units — are set to be completed between now and 2029, according to The City’s Affordable Housing Pipeline. More than a third are within seismic hazard zones, according to a map provided by DataSF, as well as the pipeline document.

When the City and County of San Francisco Hazards and Climate Resilience Plan was released in March 2020, the report revealed that more than half of all industrial parcels, a third of all commercial parcels and exactly 39% of all critical facilities (schools and hospitals, for example) were located in seismic hazard zones.

And none of that is a coincidence, says Corey Smith, executive director of the Housing Action Coalition.



As The City map shows, much of San Francisco’s planned affordable housing stock is going up in these hazard zones. Meanwhile, citywide residential construction activity, such as home renovations, is distributed relatively evenly throughout The City.

That’s because San Francisco is building up an affordable housing stock in the only places it can.

“Zoning determines height and bulk, what we are able to build and where on each individual parcel. Every single parcel in The City has a zoning rule,” Smith explains. “And a long time ago, The City decided, OK, we’re going to concentrate all of our big buildings on the east side of The City. For a variety of reasons, that was the wrong decision.”

The 1978 down-zoning of The City made downtown and the eastern waterfront the epicenter of new development. Down-zoning refers to rezoning of land to make it more restrictive to development. So, much of The City was limited to a certain height, 40 feet, and low-density. And it happened that the areas left for high-density, tall buildings were situated on shaky ground — such as downtown, Mission Bay and Bayview.

The down-zoning plan was strongly backed by residents who wanted to maintain the family and neighborhood flavor of The City. But at the same time, it forced large developments to build on seismic hazard zones.

Those large developments include multi-unit market-rate buildings as well as new affordable housing within them — now mandated by the Inclusionary Affordable Housing Program. This program requires new residential project develolpers with more than 10 units to pay an “affordable housing fee” or offer a percentage of the units at “below market rate.”

“If you look at the zoning map, which is a map that says where apartments can or cannot be built, multi-story multi-family apartment buildings … that’s where affordable housing is legal or not legal as well,” says Smith. That is also where large swaths of The City’s seismic hazard zones are centered.

And so the placement of affordable housing projects is dictated by the intersection of developers needing to build nearly 100 units per parcel to make a project worthwhile and zoning laws that designate the east side, in all of its seismic vulnerability, as the only place for developments of this size.

A wrinkle in this scenario is the increased cost of building in seismic hazard zones. In order to accommodate safety regulations, construction costs balloon. This makes pricing units below market-rate all the more challenging, says Jeff Brink, CEO of DCI Engineers.

Just what is a seismic hazard zone?

Seismic hazard zones delineate areas in which earthquake-related hazards are concentrated. On the map above, created using data provided by the City of San Francisco, these risks include “liquefaction, earthquake-induced landslides, overlapping liquefaction and earthquake-induced landslides” that may occur during an earthquake of high magnitude.

San Francisco is expected to experience a high caliber earthquake in the coming decades — related to one of two nearby fault lines, the Hayward Fault and the San Andreas Fault. OneSF, The City’s office of resilience and capital planning, which works to plan and fund programs to strengthen The City’s infrastructure, predicts that “there is a 72% probability of one or more (magnitude greater than) 6.7 earthquakes from 2014 to 2043 in the San Francisco Bay Region.”

San Francisco is no stranger to catastrophic quakes. On April 18, 1906, The City was near the epicenter of an earthquake of estimated magnitude 7.9, though studies using different techniques offer different values. The disruption ruptured along 296 miles of the San Andreas fault line. Death and destruction swept The City from the quake and the subsequent fire.

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“Earthquake-induced landslide risks” are scattered along the hills and cliffs of The Outer Richmond, Sea Cliff, Presidio, Lake Shore, Bayview Heights, Midtown Terrace, Twin Peaks, Clarendon Heights, Golden Gate Heights, Forest Hills, Diamond Heights, the Castro, Dolores Heights, Noe Valley, and Yerba Buena Island, according to The City’s hazard-resilience plan.

Liquefaction risks, considered potential “ground failure,” are concentrated in SoMa, the Mission District, Hunters Point and areas near the water, such as the Marina District and Treasure Island. These also happen to be the areas where much of The City’s planned affordable housing is designated.

So what is the city doing to protect housing?

The soft-soil mandate is part of a 30-year program currently underway in San Francisco to mitigate risks, called the Earthquake Safety Implementation Program (ESIP). Its work first began in 2011, following the results of the Community Action Plan for Seismic Safety, which determined that The City was ill-prepared for a major earthquake.

The sf.gov page dedicated to the program states that the report found that an earthquake scenario would “devastate The City’s housing stock, and could have long-term implications on The City’s affordability to middle- and low-income residents, who would be displaced for years. Hundreds of people could be killed and thousands could be injured.”

The Earthquake Safety Implementation Program developed 50 tasks to be completed by The City between 2012-2042 to prevent this kind of devastation, and is working in tandem with The City’s Hazards and Climate Resilience Plan to reduce overall risks. Also at play is the California Seismic Hazards Program, created by the Seismic Hazards Mapping Act in 1990. It was introduced following the Loma Prieta quake in 1989 to reduce further damage and loss of life in the event of an earthquake.

In collaboration with the Department of Conservation, California Geological Survey, seismic hazard maps are designed and distributed. Information from past faults and earthquake activity, seismic wave behavior and site-specific conditions are combined to determine risk.

The program also requires San Francisco to use the hazard maps in land-use and development planning. According to The City, anyone developing in hazardous regions could be required to investigate the associated risks and work to mitigate potential harm in the event of an earthquake. The Seismic Hazards Mapping Act also requires real estate brokers to disclose the potential risk of their sites at the time of sale.

Beyond just maps, mitigation programs work to undercut risks. A pre-development plan for the Star View Court project, for example, outlines the “geotechnical improvement program” that Treasure Island is implementing. The plan includes tactics such as “improvement of island perimeter,” “vibratory compaction” and “surcharging.” Vibratory compaction will work to strengthen the soil’s integrity, while surcharging applies a lateral pressure to soil areas to further compact the earth.

Mitigation strategies for existing buildings

San Francisco’s required mitigation strategies often call for capital. The City’s retroactive soft soil mandate, for example, requires a seismic retrofit of wood-frame buildings over three stories built before 1978. The cost of these retrofits range from $3,000 to $7,000 according to Earthquake Brace and Bolt, a grant program under the purview of California Residential Mitigation Program. The city also offers grants to eligible residents, as well as an option to finance the retrofit.

The City’s resilience plan also dictates proactive approaches to preparing for seismic disturbances, such as plans to “continue to meet housing production goals,” “continue to advance the Sewer System Improvement Program,” and “implement the SFMTA Parking Strategy.” The status of all projects at the time of the report’s publication were “sustaining,” meaning at the time of the report, the strategy was already in effect and is an active and ongoing aspect of the mitigation plan.

Outlined in the Earthquake Safety Implementation Program and currently in progress are:

• San Francisco’s Tall Buildings Study, which is evaluating the impact of a quake on buildings over 240 feet and determining strategies for resilience

•The Private Schools Earthquake Evaluation Program, which requires a seismic evaluation of these properties

• The Facade Inspection and Maintenance Program is somewhat self-explanatory and applies to certain buildings over five stories.

• The Chimney Mitigation program, which evaluates risks posed by The City’s masonry chimneys and determines methods of mitigation based on the data.

As the days count down toward the 30 years until the earthquake safety plan is fully implemented, more mitigation strategies kick-start — on pace with city development.

In the meantime, there’s really only one way to find out if The City’s considerations will be enough to counteract the catastrophic risks at play.

And that’s to wait for the quake.   

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