Palo Alto evaluating regulations to improve safety of seismically vulnerable buildings

 

Palo Alto City Council voted Nov. 13 for city staff to begin drafting new regulations for certain buildings at risk of earthquake damage, the latest step in a multiyear effort to understand and improve the seismic safety of the city’s older buildings.

A structural engineering firm contracted by the city found that in a magnitude 7.9 earthquake on the San Andreas Fault, city buildings could suffer roughly $2.4 billion in damages.

Retrofitting the most vulnerable buildings could cut these potential earthquake damages nearly in half and save lives, but the city still needs to decide how exactly it will encourage improved safety and what types of buildings it will focus new regulations on. There is currently no mandate for property owners to address this risk. The firm hired by the city and an advisory group of local stakeholders have compiled a wide-ranging list of options for action.

The City Council voted unanimously, without discussion, for its Policy and Services committee and city staff to consider the options and begin drafting new regulations if it sees fit.

“The next phase of this is definitely going to take a bit more work,” said Peter Pirnejad, Palo Alto’s development services director. He guessed that it “could take another 12 months” before the city has any new earthquake policies.

Palo Alto began looking into seismic risks in 2014, after an earthquake near Napa caused significant damage there. It hired the structural engineering firm, Rutherford + Chekene, to study Palo Alto’s risks. The research excluded single family and two-family homes, focusing instead on apartments and commercial buildings. In April, the firm released its final report, which highlighted four new categories of seismically vulnerable buildings whose dangers the city could try to mitigate through a variety of strategies, which range from increasing public disclosure to mandating retrofits.

The risks Palo Alto faces

Palo Alto has a large number of “soft-story” buildings, which have first floors with inadequate support for upper levels and could collapse in an earthquake. The assessment estimated that Palo Alto has 294 soft-story buildings with wood frames and 37 with concrete structures. Many of these are apartments built in the 1960s and 1970s with large garage openings on the ground floor.

Tom Holzer, an engineering geologist at the United States Geological Survey and adjunct professor at Stanford University, said the high number of soft story buildings and relatively low cost of retrofitting them make the category a good target for regulation. Holzer was part of the advisory group of property owners and developers, policy experts and other local advocates that worked with the Palo Alto building department and the structural engineering firm to make general recommendations to the city.

The Rutherford + Chekene report estimated that every dollar spent improving wood frame soft-story buildings could save $4 worth of damage in the scenario of a magnitude 7.9 earthquake.

A 2015 study by the USGS estimated that an earthquake of this size—comparable to the 1906 San Francisco earthquake—has less than a 20 percent chance of happening in the San Francisco area in the next 30 years, and a less than 5.7 percent chance of happening on the Northern San Andreas fault, which is especially close to Palo Alto.

But an earthquake with magnitude of at least 6.7, almost as large as the 1989 Loma Prieta earthquake that destroyed many soft-story buildings in San Francisco’s Marina District, has a 72 percent chance of occurring somewhere in the area in the same timeframe.

San Francisco is one of a handful of cities in the Bay Area that have a mandatory soft-story retrofit program. The Palo Alto advisory group supported creating a similar program, which would force all soft-story buildings to either be improved on a fixed timeline or when they are next sold or renovated. They also supported improving public disclosure about seismic risks and addressing other types of seismically dangerous buildings.

While California tends to set safety codes for new buildings at the state level, cities have some leeway in determining how to deal with the seismic risks of existing ones.

Palo Alto’s current earthquake policies focus on buildings with unreinforced masonry, which can collapse and kill people during earthquakes.

The state passed a law in 1986 forcing local governments in earthquake prone areas to inventory these structures, but it didn’t mandate retrofits. Palo Alto required owners of these and two other categories of old buildings to evaluate seismic risk and offered them zoning and financial incentives to retrofit dangerous buildings. An inventory updated in 2014 found there were still 10 buildings with unreinforced masonry that had not been addressed. The advisory group suggested these should be demolished or fixed.

The cost of seismic safety

Handling the cost of safety improvements has been a key challenge throughout the seismic review process.

“In general, these types of processes go very, very slow, and they’re highly politically fraught,” Dana Brechwald, a planner and earthquake specialist with the Association of Bay Area Governments, an umbrella organization of local governments, said. Brechwald was part of the Palo Alto advisory group.

“I think everyone acknowledges that there’s a problem,” she added. “Nobody doesn’t think that it’s worthwhile to protect our housing. … [The problem is] dealing with all the accessory issues like who pays for it, where does the money come from, does it affect renters.”

In a more affordable housing market, Brechwald said, renters could vote with their dollars to live in safer buildings and incentivize retrofitting. But that’s not feasible in Palo Alto, where an Oct. 16 City Council discussion of earthquake safety was tabled after rent control dominated the entire meeting.

The structural engineering firm’s report estimated that retrofitting wood frame soft-story buildings would cost $12 per square foot on average. Average costs for retrofitting the other types of vulnerable buildings considered in the study range from $10 to $42 per square foot.

Holzer, the geologist, noted that the temporary displacement some retrofitting could cause to residents was especially unappealing in the current housing shortage. But he added that housing destroyed in earthquakes could cause displacement too.

“When I first started working in this business, I used to think ‘Okay, let’s solve it,’” Holzer, who has worked for the USGS for more than four decades.

“I’ve come to the realization that the world is a lot more complicated than my simple seismic hazard view,” Holzer said. “There’s economics here that is well beyond my ability to control, and it’s just going to be a slow process that we go through.”