Ask Us: A map of bedrock vs. landfill
Feb.15, 2008 in
Ask Us, theFrontSteps
Where readers ask and we try to answer:
Can you tell me how I can get a map of all the SF neighborhoods that would show me what areas are bedrock vs. landfill.
Thanks,
C
First, you’ll want to know your Seismic Hazard Zones.
Then, you’ll want to get in there a bit further and really have a look. You can find this map at http://geomaps.wr.usgs.gov/sfgeo/liquefaction/susceptibility.html.
Here is another liquefaction map that you can also peruse. This one you can zoom in to street level. Remember, red=bad.
Hope this helps. I’m sure there are some readers that might even know of better maps, so let’s hope they chime in.
Thanks for reading and thanks for asking.
[Update: this high resolution photo taken after the 1906 Quake is amazing.]
February 15th, 2008 at 6:21 pm
Hmmmm… Mission bay is marked red=very bad.
Here I think that the type of structure becomes a big factor for safety. Older structures may not fare well. I am hoping that the newer developments are designed considering the fact that they sit on a liquefaction zone.
Hopefully whoever in the city who is approving the Mission Bay projects is not asleep and has required sturdier construction for this high risk zone.
Can anyone confirm ?
February 17th, 2008 at 11:01 pm
I’m not sure if there are city statutes about building on these zones, but I can say that I know the UCSF buildings that have been erected in that region are supposed to be built on beams that extend to the bedrock near the bottom of the bay. Whether or not residential construction is also doing so I don’t know.
February 18th, 2008 at 9:41 am
The thing that really gets your attention is how many elevated freeways circumnavigate the ‘red zone’!
One of the lessons learned from Loma Prieta was ‘soft story’ construction and liquefaction, illustrated best in the Marina district in ’89. All those multi-sotry apartment buildings over garages that came down once the soil lost its bearing capacity.
All the new stuff in Mission Bay – constructed over deeply driven steel (or precast concrete) piles, then tied together w/a robust concrete slab. The biggest issue will be the buildings standing firm, while all the site work (sidewalks, courtyards, landscape) sinks a few inches (or more).
In the older SF neighborhoods, wood-framed stucco buildings fare quite well in quakes (look around – most everything was built before ’89, and lots before ’06). The scarier things are the fires after the quake!
February 18th, 2008 at 1:32 pm
The client – It looks as if the seismic standards are geared to ensuring that buildings don’t collapse in a quake. Their goal is to protect the safety of the occupants, not ensure that the building survives. So people in those buildings will likely survive the big one, but the building may need to be torn down and rebuilt to make the site functional again.
I agree, the fire after the quake is what we really need to worry about. It always makes me wonder what sort of crisis planning the SFFD has done. Are they able to extinguish multiple fires considering that many streets will be blocked by rubble and abandoned/gridlocked cars ?
February 18th, 2008 at 8:00 pm
The area in The Marina right below Fort Mason is all bedrock. That area, along with Cow Hollow, Pac Heights would be gold mines if someone could ever build.
February 19th, 2008 at 12:00 am
I recently did a City Guides walking tour of the SFPL Main and was surprised to learn that “in the event of a shock, an 18-inch space around the circumference of the building allows the structure to move independently from the ground.” In other words plates that surround the building are designed to collapse and create a gap for the building to move around. Take a look sometime- it’s easy to identify them. I wonder how many homeless nappers we’ll lose in that chasm when the big one hits.
February 19th, 2008 at 9:51 am
hoegaarden. The city earthquake planning is not a secret at all. Actually, it’s so public that if you have about 20 hours to spare, you can get a FREE FUN AND AMAZING full coverage of the subject and get your diploma and a (free) cool kit. (the training addresses a very real local 8.0 with the collapse of ALL infrastructures). Here: SF NERT (look for the “training” and “classes” links)
the bad news is that YOU are already part of the plan laid by the city – either you are ready, or you’re not prepared (you as in what you represent: your personal body, your living quarters, your family, your pet, your car, your office at work etc).
PS: for all other readers, this training is a must for anybody with ties to realestate in SF (RE agents, homeowners, landlords, renters, contractors, architects etc). For Bay Area readers, check the CERT website for your local training. For non-US readers, please check our award winning website 72 Hours that applies to virtually anywhere in the world.
February 19th, 2008 at 4:29 pm
Hi Sophie – Thanks for the link. NERT is definitely worthwhile. I’ve got first responder training already knowing that when the big one hits there’s no way that the medical professionals will be able to keep up for the first 24 or more hours.
Actually what I was concerned about was specifically the SFFD’s ability to fight multiple fires after the big one. NERT may be able to help, but there’s only so much that can be done with garden hoses.
February 19th, 2008 at 10:24 pm
This from Sophie via email:
I know it’s paper vs webbased, but I thought you’d like to check one of the latest paper books about SF.
“San Francisco in Maps and Views by Sally Byrne Woodbridge,”
http://search.barnesandnoble.com/booksearch/imageviewer.asp?ean=9780847828715
it covers every type of map you can find of san francisco, from the gold rush, to the great fire, to the walk and bike map of this century, to 3D representation of the sky crapers. AND some earthquake maps.
For those, additional links and infos are spelled out for further internet browsing.
February 19th, 2008 at 10:54 pm
since we’re on the subject, check out this amazing high res picture of san francisco in 1906 right after the big quake:
http://upload.wikimedia.org/wikipedia/commons/b/b3/San_Francisco_in_ruin_edit2.jpg
let’s hope this never happens again
October 21st, 2011 at 6:09 am
Looking at the maps above I am in the “white area” however butted up against a solid red. I am at 3685 17th St. 17th/Church and my backyard is the Mission High School. Can you tell me whether I am on safe land or not? Or if I have a sound structure to withstand earthquakes?
Thanks
Evan
October 21st, 2011 at 8:17 am
Sorry Evan,
I’m not a seismic or soil stability engineer. I can only point you in the direction of those who are. I would advise contacting somebody from one of those websites that can speak to the stability and location of your specific structure.
March 4th, 2013 at 8:51 pm
http://gis.abag.ca.gov/website/LiquefactionSusceptibility/index.html
updated link for the ABAG map (last resource above).
if you are any close to a colored zone, just make sure you identify the type of risk, and know you can live with it.