Today's 105th anniversary of the 1906 San Francisco earthquake comes as the world is still reeling from Japan's devastating earthquake -- causing many to wonder what area is next.
Earthquake scientists say there is a 62 percent chance of an earthquake with a magnitude 6.7 or greater striking the Bay Area by 2032. In addition, areaalong the Rodgers Creek Fault -- which runs through ncluding the Healdsburg area.
agency are exploring the s in a series of articles that began earlier this month.
In Sonoma County, private homes could be at risk too. Regional and local building officials say it is nearly impossible to determine how the roof you’re living under will fare during the next big earthquake.
Soils structures can vary drastically from site to site, and cities don’t keep track of when houses were built, or to which building code. The older the house, the greater the risk of collapse.
Structures that could fail in an earthquake include:
- Soft story buildings — normally houses or apartment buildings with a garage or business on the bottom that can’t hold up weight during an earthquake.
- Single-family homes, which can slip from the foundation because they’re not adequately bolted down, or because walls aren’t reinforced .
- Older mobile homes, built prior to 1995, which are likely to shift off their support during an earthquake.
Finding Out About Your Home
One way to begin assessing how well your home will do in an earthquake is looking first at the year it was built.
“Different jurisdictions have more control over their retrofitting than others,” said Michael Whitaker, Santa Rosa’s chief building official, who many local authorities joke is the "guru of building codes."
“It’s really a matter of identifying your building,” Whitaker said.
A quick easy test, from the Association of Bay Area Governments website, can help determine if your home will survive an earthquake. Tally up the points and keep track.
- Was your home built before 1960? (five points) 1961-1978? (three points) 1979? (one point)
- How tall is it? Two ore more stories with living area above garage? (five points) Split level or on a hillside? (six points) One story, with three or more steps to the front door? (four points) One story, with less than three steps to the front door? (one point)
- What intensity does the shaking intensity map show for your neighborhood? Dark red or black? (seven points, and Rohnert Park and Cotati are in the dark red zone, so we needn't go further)
According to ABAG, if you counted 13 points or more, "it probably needs to be evaluated to see if it is strong enough to keep you and your family reasonably safe, unless it has been strengthened in the last few years."
This test for single-family homes varies slightly for apartment buildings. The findings can differ in multi-story buildings depending on what material the walls are built from and if the walls are reinforced. The most important thing to know is when your house was built, if you don't know any of this other information.
Shaking and liquefaction during an earthquake cause the most damage. Houses can sink into the ground, tip over, crumble or split in half. But each structure could experience a different level of disaster depending on where it's situated in relation to the fault, how it's built, the type of soil the house is built on and the magnitude of the quake.
“When I first started in ‘79, the codes were plain and simple,” said Greg Adams, Rohnert Park’s building inspector, who started with the city in January. “But every time there’s a seismic event, they look at where buildings fail and determine what we need to do to not let that happen next time.”
Many houses built prior to the ‘90s wouldn’t meet minimum building code standards today, Adams said. But, to retrofit them would be expensive and time consuming.
“The important thing is that they met code when they were built,” he said. “The code really doesn’t go into retrofitting older houses, it’s more like ‘if you want to retrofit, here’s how.’”
“It’s really up to each resident,” he added.
Glenn Schainblatt, who runs the Cotati and Sebastopol building departments, has spearheaded a campaign in Sebastopol to identify and retrofit vulnerable structures. So far, he’s tallied 55 that need to be retrofitted.
“Anything built prior to the ‘70s really is kind of dicey, it wasn’t really built to code,” Schainblatt said. “But just because they’re old doesn’t mean they’re dangerous — you just never know.”
The law only requires unreinforced masonry buildings, schools, hospitals and government buildings to be retrofitted in what’s called seismic zone four, an indicator that we’re dangerously close to a fault. But it is residences that could absorb the majority of the damage, mostly because statewide building codes only require new development to be built to withstand an large earthquake.
“People need to understand that the buildings code is a minimum standard, so when an earthquake strikes, it’s only required to get you out of the house alive,” said Danielle Hutchings, the earthquake and hazards program coordinator for ABAG.
“It doesn’t say anything about every being able to get into the house again," Hutchings said. "That’s why we think most older buildings need to be retrofitted.”