It's definitely not a question of "if," but "when." There are so many faults in the Bay Area (and Los Angeles) capable of producing a large quake: San Andreas, Hayward, Calaveras, Rodgers Creek are the main ones with many lesser-known faults running parallel to these. I was in Santa Rosa in 1989 when the "sorta big one" (as it was called) struck in the Santa Cruz Mountains about 125 miles to the south. There was much damage and dozens of deaths, mostly from a collapsed double-deck freeway (I-880) in Oakland. To think that this wasn't near as devastating as it could have been is very frightening. The power has to be experienced to be totally understood. As much as I love the Bay Area, I hope I'm not there when the true "big one" hits.
The 1989 Loma Prieta quake was 6.9. The Great Quake of 1906 was estimated to be anywhere from 7.8 to 8.3. At the time of the 1906 quake, there was a total of less than 700,000 people living in all nine Bay Area counties, including 350,000 in SF. Today, there are just under 8,000,000 in those same nine counties, with nearly 900,000 in SF (which is just 47 square miles). Damage from an 8.0 quake in the Bay Area today would be nearly incalculable. Much of the populated area there is built on unstable land that was used to fill in parts of San Francisco Bay (ironically, debris from 1906 was used to fill in this land). This poses issues for any structure built on such land areas, but particularly would be troublesome for skyscrapers. Many of SF's newest towers have been built in SOMA (South of Market), which is a flat, mostly reclaimed area. Some towers do NOT have support pilings that go down to bedrock to keep them stable, notably the Millennium Tower, a luxury residential highrise approximately the same height as 801 Grand in Des Moines. The most recent story on this with info on how much it has sunk and how far it's leaning:
For those who are interested, I'm including a video from KGO-TV San Francisco, which was carrying the broadcast of the World Series live from Candlestick Park that afternoon. It begins with the Series when it strikes, then cuts to KGO's news room and we see how the anchors learned of everything that happened live, including a section of the Bay Bridge collapsing (that entire eastern span has since been replaced) and the collapse of a quarter mile section of I-880, a double-decker freeway. The massive fire in San Francisco's Marina District had not yet been reported. It's fascinating to see things play out. We didn't have power where I lived in Santa Rosa until later that evening, so we didn't know a lot of what was going on until late that night.
