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Stanford professor Zoback used to work for Risk Management Solutions and co-authored the 2008 study. She says a big lurch of the Hayward Fault would likely kill hundreds, and possibly thousands, of people. "But probably not tens of thousands," she said.
A 2010 report from San Francisco's Community Action Plan for Seismic Safety Project estimated that a 7.2 earthquake on the San Andreas fault would make 27,000 buildings in San Francisco — about one in five — unsafe to dwell in. Nearly 4,000 buildings would need to be demolished, too. The report also estimated the earthquake would start more than seventy fires, which could destroy another 2,000 to 3,000 buildings. Total damages from the earthquake and fire might run $34 billion. Three-hundred people could die. The report warned that a repeat of the 1906 quake could kill nearly 1,000 people.
The injury and death toll would have much to do with the hour that the earthquake strikes, Zoback says. The worst time of day to experience a large earthquake in the Bay Area would be mid-afternoon, when many people are at work. "Having lots of people in buildings is the concern, since, if just one of them collapsed, you could have lots of people killed," she said.
The potentially disastrous consequences of a mid-sized earthquake striking a city in a developed nation were seen on Tuesday, January 17, 1995, in southern Japan. At 5:46 in the morning, a magnitude 6.9 earthquake caused several feet of lateral and vertical displacement of two adjoining tectonic plates. The city of Kobe was left in ruins, and more than 6,000 people died.
Though the Loma Prieta quake gave millions of people an idea of what a big earthquake feels like — and also revealed weak points in social infrastructure and building codes, and helped officials map out developed areas of artificial fill prone to disastrous shaking — it wasn't a serious field test of the Bay Area's seismic tolerance, according to Rundle.
"So it's a very big problem," he said. "An earthquake [on the Hayward Fault] is going to be much stronger and very different than what we saw in Loma Prieta."
The Most Vulnerable
Near Lake Merritt along Perkins Street, hundreds of people live in multistory apartment buildings. The ground level of many of these structures is dedicated to parking — a convenient feature for residents who like to keep a car handy. However, this outdated building design, virtually void of supportive cross walls at the street level, makes such buildings very dangerous.
Experts say they are likely to collapse in an earthquake, as the ground floor gives way, followed by the floors above. In China in 2008, thousands died in the city of Beichuan when a 7.6 magnitude shaker turned hundreds of such so-called "soft-story" buildings into bloody rubble heaps.
Some of the worst damage in the '89 quake, in fact, was seen in soft-story residential buildings in San Francisco. And in the '94 Northridge earthquake in Los Angeles, sixteen people — probably sleeping at the time — died in a single soft-story building when it crashed down upon its own foundation at 4:30 in the morning. There are estimated to be about 15,000 such buildings in Los Angeles today.
Oakland has about 1,500 soft-story structures vulnerable to collapse, according to estimates from the city's Resilient Oakland Initiative, launched in March 2015.
A source who did not wish to be named said that upgrading soft-story buildings has slipped dangerously low on the priority list of Oakland officials. The city's chief resilience officer, Kiran Jain, did not return a call to discuss this issue. Dana Brechwald, resilience planner with the Association of Bay Area Governments, also did not respond to two calls and two emails.
The city of San Francisco is doing better and now requires landlords to retrofit soft-story buildings with support pilings at the ground floor. Still, more than 5,000 soft-story, multi-unit buildings remain. And about 120,000 people live in them, according to Patrick Otellini, San Francisco's director of earthquake safety. If these buildings aren't retrofitted, he says, many people are going to die or be injured. Otellini says the retrofit work should be completed by 2020.
If an earthquake strikes before then and destroys a significant number of San Francisco's soft-story residential buildings, the city will face an instant housing crisis. That, Otellini explains, is because most of the units within these buildings are currently rent controlled. If these buildings collapse, they will be rebuilt in the absence of such tenant-protection codes. Former residents would likely be priced out of the housing market.
"Then, we could have 100,000 people without homes," he said.
Otellini noted that the aftermath of earthquake destruction is not limited to, or focused in, low-income neighborhoods.
While San Francisco's Marina District received lots of attention after many soft-story buildings collapsed or were damaged in '89, the problem, he said, occurred across San Francisco rather equally. "The one thing that binds these people together is the rent-control aspect," Otellini explained. "They do tend to be people who don't have [the] security of home ownership."
He also says soft-story structures are hardly the extent of the Bay Area's quake vulnerability. "They're just the low-hanging fruit."
Other structures less easy to identify and inventory are also prone to breaking apart in a big earthquake. These include buildings constructed decades ago with weak steel welds and made with brittle types of concrete. Otellini says public schools may even be in better shape than private schools, since the former have been subject to greater structural scrutiny and building codes.