What Would Happen if Haiti Quake Happened Here? Actually, 2009 Report Analyzed Just That.

There are three answers to the query of what effect a magnitude 7.0 quake would have on San Francisco:

1. We'll see!

2. The city will do better than you'd think but worse than you'd hope

3. An extensive 2009 report prepared at the behest of the Department of Building Inspection pretty much examined exactly this question.

That report, "Here Today, Here Tomorrow," was written largely to address the looming earthquake disaster of San Francisco's "soft-story" buildings. These are wood-framed structures of three stories or more with five or more units -- often with a garage or business on the ground floor -- and constructed prior to May 21, 1973. Here's what the study claims:

• There are 4,400 such structures standing in San Francisco and 2,800 are "significantly" vulnerable;

• If a 7.2 quake were to emanate from the San Andreas Fault, between 43 and 85 percent of the significantly vulnerable structures would be rendered uninhabitable;

• One-quarter of these buildings could collapse -- that's up to 850 buildings;

• Eight percent of the city's population live in the 29,000 residential units within those 2,800 problematic structures. That's 58,000 people residing in structures with a real possibility of collapse;

• Those buildings also house 2,100 businesses, employing around 7,000 people.

• Retrofitting the most vulnerable structures would cost about $260 million. Not retrofitting them would incur $1.5 billion in rebuilding costs.

And yet, things could actually be worse than these predictions. While the quake that leveled Haiti registered 7.0 on the Richter Scale, what engineers keep a closer eye on are "shake maps" that actually give the acceleration of the tremor -- which is what actually causes buildings to move. Glancing at the shake map for Haiti, San Francisco's Chris Poland -- CEO and Chairman of Degenkolb Engineers -- sucks in his breath. "These are really big numbers," he says.

"I expect our construction will perform much better -- but we have 150 years of buildings, many of which don't conform to modern codes," he said. "You will find isolated examples of collapsed and highly damaged structures, and some casualties."

And, since earthquake safety is based on a building surviving a quake -- not on its ability to be structurally sound afterward -- even a 7.0 quake could render scores of thousands of San Franciscans homeless.

Essentially, the answer to any query about how San Francisco will fare in a big quake always comes back to the first one we posited -- we'll see.