Safe Enough to Stay - ABAG Earthquake and Hazards Program

Safe Enough to StaySan Andreas earthquake. In every neighborhood in the city, morethan 10 percent of the housing units would become unsafe tooccupy. The neighborhoods that will see the most damage are thosewith large numbers of multifamily buildings, which are generally morevulnerable than smaller residences, and those that have significantareas of soft or liquefiable soils, which can experience magnifiedshaking and ground failure. (See Figure 2, page 13.) Figure3 (page 14) shows estimates of the percentage of unsafe units inall districts. Estimates suggest that the Marina district would be hithard, with nearly half of housing units there unsafe to occupy. TheRichmond district would also suffer significant amounts of damagedhousing, with an estimated 35 percent of units unsafe to occupy dueto the type of housing in the neighborhood and its proximity to theSan Andreas Fault.Known structural deficiencies are behind this predicted damage.Wood-frame soft-story residences with three or more units wouldaccount for two-thirds of the housing units citywide that could notbe occupied. Typically, a soft-story building has large openings atthe ground level, such as garage doors or store windows, and fewinterior walls, making the ground floor much weaker and moreflexible than the stories above. In an earthquake, the ground level cansway excessively and collapse. Construction patterns are differentin various parts of the city, so the types of structures responsible forhousing damage would vary by district, as shown in Figure 4 (page15).In the expected earthquake, all neighborhoods would experienceheavy damage, but some would see more housing loss than others.Estimated housing losses range from 11 percent in the Inglesidedistrict to an alarming 50 percent in the Marina. The followingsections explore what some of the consequences of this housingdamage might be in selected districts with large housing losses —Downtown, the Marina, the Mission and Western Addition — andhow damage to specific districts would affect the city as a whole.For more about the varying impacts on different neighborhoods, seeAppendix I, page 32.DowntownIn addition to the downtown financial district, CAPSS defines thisdistrict as including the Tenderloin, the south slope of Nob Hill, muchof SOMA and most of Chinatown. Encompassing some of the oldest,densest and most historically rich parts of the city, the downtownarea contains approximately 54,000housing units, the largest number of anydistrict, in addition to housing more than250,000 of San Francisco’s jobs. It is alsothe city’s least affluent district, measuredby median household income, with largeconcentrations of single-room occupancy54,000Housing units15,000Units rendered unusableby the expected earthquakebuildings and other types of affordable housing. Many elderly people,new immigrants and non-English speakers live here. After theexpected earthquake, nearly 15,000 housing units downtown (27percent) would be rendered unusable. Approximately half of theseunits are in wood-frame soft-story buildings with three or more units;the rest are located in non-wood structures, including older concreteframebuildings and retrofitted unreinforced masonry buildings thatare still vulnerable. These non-wood structures are particularlyproblematic because some of them house a large number of unitsand they can be difficult and costly to retrofit. Housing losses in thisdistrict would be expected to displace many lower-income residentswho would depend heavily on city services after the disaster.flickr user reallocalcelebrity (John Morrison)16 SPUR Report > January 2012