Quakes in SF (San Francisco, Hayward, Sunnyvale: apartments, to rent, how much)

[headingwest236]

I know my other threads turn into this, so I figured I'd start a new one. I'm moving to San Francisco from the east coast, and I realize I'm making myself vulnerable to the high earthquake risk in the area, but I still have a few questions:
#1 How frequent do you get them? Once or twice a year? A big one (7 or greater) every 10 or 20 years?
#2 How much worse does liquefaction make the shaking, and is it a bad idea to rent in a liquefaction area? All of the apartments that I'm considering happen to be in SOMA/Mission Bay, which I know is a liquefaction red zone. This isn't a fiscal issue since I'm renting, but I really don't want my building to fall over or have a fire from a gas leak, due to the ground failing. BTW the one I'm looking at most was built in 2007, so does that mean its safer?
#3 When there's the big one everyone's talking about, will you have to evacuate the city, and why? I assume bridges would be unsafe so everyone would have to take 101/280 down the peninsula. I also don't plan on owning a car, so should I be worried about getting out?

Sorry for all the paranoia.

[ImRandy]

Earthquakes are quite frequent. The overwhelming majority are too small to feel. Big ones are rare but we have a very high likelihood of one happening in the next 30 years.

Newer buildings are held to newer standards when they're built. Older buildings are required to be retrofitted when they need major work done or when they have a particularly hazardous design like a soft story. So you can have older buildings that are and aren't as "safe" as newer buildings and you can have newer ones that are less "safe" than some older ones.

No, they will not evacuate the city. There's no point to it and it is a practical impossibility. You should not be worried about getting out but like all responsible people no matter where they live in the world you should have a supply food, water, and medical supplies for emergencies.

BTW, the USGS has a lot of information on earthquakes, preparedness, etc. You should take a look. For example this page shows a weeks worth of earthquakes (429) on a map of California and Nevada.

[capoeira]

Good questions! For an in depth study of what might happen I suggest checking out Marc Reisner's book "A Dangerous Place". It includes a hypothetical scenario of what might happen with a 7.2 on the Hayward Fault.
He identifies the lack of water and collapse of the water system as a huge problem after a big earthquake.

A shaky situation in California | BookPage

Originally Posted by headingwest236

#1 How frequent do you get them? Once or twice a year? A big one (7 or greater) every 10 or 20 years?

The three big ones were a 6.8 in 1868 on the Hayward Fault,a 7.9 in 1906 on the San Andreas Fault and a 6.9 in 1989 on the San Andreas.

October 21, 1868 Hayward Fault Earthquake

The Great 1906 San Francisco Earthquake

October 17, 1989 Loma Prieta Earthquake

The problem is that scientists think the Hayward fault repeats a big event every 150 years and the last one was in 1868.

http://pubs.usgs.gov/fs/2008/3019/fs2008-3019.pdf

Hayward Fault is our deadliest - a 'tectonic time bomb'

The buildings to avoid living in are the soft story apartment buildings with a parking structure underneath the living area. Most have not been retrofitted. Concrete buildings are also a danger.

Fewer participating in San Francisco's soft-story retrofit program

S.F.'s concrete buildings also a quake danger

These are good in depth studies of the earthquake potential in the SF area.

http://www-tc.pbs.org/newshour/indep...atc-report.pdf

Earthquake Probabilities in the San Francisco Bay Region: 2002–2031 | USGS Open-File Report 03-214

These are the shaking maps with selections for different faults.

Earthquake Shaking Maps and Information « ABAG Earthquake and Hazards Program

The worse case scenario is an earthquake similar to 1906.

Disaster is coming to San Francisco ... the question is when

[80skeys]

Originally Posted by headingwest236

#1 How frequent do you get them? Once or twice a year? A big one (7 or greater) every 10 or 20 years?

We have been living here the past year and a half, and we have felt three quakes, each one about 4.0 magnitude. They weren't bad. Just a little shaking and rumbling for a second. I was on the Caltrain for one of them and I didn't feel anything.

#2 How much worse does liquefaction make the shaking, and is it a bad idea to rent in a liquefaction area?

I've been told there are areas of San Francisco that are literally built on the rubble from old shipwrecks and there are other areas built on top of sand, and houses on these two areas are the ones that suffer most in earthquakes.

My wife works downtown around 3rd and Mission and says one of the earthquakes she felt was a very strong up-down "jolt". I was in a different part of the Bay at the tmie and hardly felt it, so maybe there's something different about the land downtown.

We have friends who have been living in the area about 6 years and they said they felt one strong earthquake about 4 years ago. Some of the books on the bookshelves and things hanging on the walls fell down. This was at their place in Sunnyvale. That was the strongest they've experienced here. The rest have been mild.

I personally don't worry about it, but to each his own.

[mdwstrnkid]

Originally Posted by 80skeys

I've been told there are areas of San Francisco that are literally built on the rubble from old shipwrecks and there are other areas built on top of sand, and houses on these two areas are the ones that suffer most in earthquakes

Much of the Financial District was built on this rubble. Many people don't know this, but the waterline used to come up close to Montgomery Street (which is currently about seven blocks away from the Bay).

San Francisco - Before the Gold Rush - 1847

They have even recently discovered wrecked ships when excavating foundations for new buildings. In 2001, they found a wrecked ship, the General Harrison, near Clay and Battery.

Bay Crossings

[California Vagabond]

I think other respondents have beaten me to it -- I've read my share of articles and web posts about earthquake risks in California, but will benefit from looking into the links already posted in this thread by others.

Still, I'll offer one favorite link of my own -- to a USGS collection of Google Earth maps: Google Earth/KML Files

[ImRandy]

Originally Posted by mdwstrnkid

Much of the Financial District was built on this rubble

And parts of the Marina are composed of rubble and fill from the 1906 earthquake which the pushed into the Bay to get rid of.

[BayAreaHillbilly]

Live on good soil (or even better, solid rock). Choose wood frame construction. Undertake the basic well known practices to strap / tie down water heaters, heavy furniture, etc. Follow Red Cross guidelines for prepper supplies. Done.

[California Vagabond]

As you mention concern about fire from a gas leak, you might also check with your landlord-to-be to insure that the building has an automatic gas shut-off valve. I don't know the regs concerning such valves for multiple occupancy buildings. They may be required; they probably ought to be. My guess is that any reasonably modern building in SOMA will have one, but it can't hurt to ask.

[Isebiel]

Originally Posted by mdwstrnkid

Much of the Financial District was built on this rubble. Many people don't know this, but the waterline used to come up close to Montgomery Street (which is currently about seven blocks away from the Bay).

I noticed the Financial District seemed suspiciously flat. But the tall buildings will have footings down in the bedrock (which is not very far down) so that's not really an issue. The streets will be a mess, though!

AFAIK, the biggest problem will be the water supply. All water for SF is piped from the other side of the Hayward Fault. There is plenty of redundancy for fighting fires, but drinking water may be an issue for a few days. That's why everyone is supposed to keep a few gallons of extra drinking water at home.