Focusing on one possible earthquake, a magnitude 7.2 earthquake on the San Andreas fault directly offshore from San Francisco, illustrates the types of consequences the City can expect following its next large earthquake. Such an earthquake could be considered expected because enough strain to produce an event of this size has built up on the San Andreas fault since 1906.
If such an event occurs, the City should expect the following impacts:
About 27,000 buildings of the 160,000 buildings in San Francisco will not be safe to occupy after the earthquake. About 73,000 more buildings will have moderate damage but will remain usable. Most of the damaged buildings will be wood-frame soft-story buildings, which make up more than half of all buildings in the City. Other structure types, notably concrete buildings built before 1980, will also suffer heavy damage.
About 3,600 buildings will need to be demolished and rebuilt. Many of these will be older and architecturally valuable buildings; some will be historic resources. The City will permanently lose the character and feel that these buildings contribute. It will also permanently lose any rent-controlled units in these demolished buildings, due to state law.
Two hundred to three hundred people could be killed, and 7,000 more could have injuries requiring medical care. If the earthquake occurs during the day, older concrete commercial buildings will be responsible for the largest share of casualties. If the earthquake occurs at night, wood-frame soft-story and older concrete residential buildings will cause the most casualties. Casualties could be much higher if even one large, densely occupied building collapses.
Earthquake shaking sparks fires (Figure B). This scenario is likely to ignite more than 70 fires simultaneously, while impeding the San Francisco Fire Department’s ability to respond quickly. This means some fires will burn unchecked for hours. An estimated 2,700 additional buildings could be destroyed by fire, including 5,800 housing units. Damage from fire could be much higher or lower than these estimates, depending on weather, wind, and many other factors.
85,000 housing units would not be suitable for occupancy and would take months to years to be repaired or replaced. Rental and low-income housing would be the slowest to come back.
Economic losses will be huge. The cost for owners to repair or replace their damaged buildings could be $30 billion. Most of this damage will be uninsured. Only 6 to 7 percent of home owners in San Francisco carry earthquake insurance, although coverage is higher for commercial properties. An additional $10 billion could be lost in damage to building contents, loss of inventory, relocation costs, income losses, and wages directly linked to this damage. Post-earthquake fires could add over $4 billion to these losses. Secondary economic losses, stemming from reduced business and household spending, would increase economic hardships.
The glaring statistic is that “Only 6 to 7 percent of home owners in San Francisco carry earthquake insurance” – that’s an outrage, and the current Mayor and indeed, everyone, should make increasing this to at least 30 percent top priority, and without breaking the banks of San Franciscans.
Stay tuned.