apocalypse lazyweb

PBS used to have this Map-a-Blast page where you could type in your address and select a megatonnage and get a customized map of the destroyed areas. It was pretty sweet, but it's gone (replaced by static text.) There's another site that has interactive blast maps, but only for paltry 10 kiloton blasts.

But my question today for you, the lazyweb, is this: how badly would San Francisco fare against a Pacific tsunami? Surely someone has done simulations of this, but it's un-googleable due to the large number of things named "tsunami" that have nothing to do with tsunamis.

I'm wondering whether Twin Peaks would deflect it at all, or whether the waves would roll right on through to Oakland.

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31 Responses:

  1. jesus_x says:

    The bridge would probably be damaged, and the Bay area would definetly see a lot of flooding, but the fact that the bay has a small opening would help shield a lot of the massive in-rush of water. There would still be some sizeable waves rolling on land, but the channeling of the water through the will force the waves to propogate from the mouth of the bay, rather than an entire coastline like the Indian Ocean tsunami did.

    Looking at a map, I think the waves would see a magnification effect so the bridge would see a sizable smack, I'd hate to be on it when a tsunami hits. But once it hits the bay, it'll start to spread out concentrically, and the narrow mouth would decrease the volume of water both in and out, so flooding would wind up being a bigger problem than the smashing waves. The water level would rise somewhat slower, which is good, but it would run out slower too, which would be bad. Also, anyone on the water better make peace with their God in a hurry. The closer to the mouth you are, the faster the water will be moving in either direction.

    • jesus_x says:

      Also, as I look at a map, I'd hate to be anywhere between I580 and I80 (which over here on the east coast is pretty darn close to where I am right now). That'd get the worse of the smashing wave effect, being opposed to the bay mouth.

    • g_na says:

      The Bay isn't really an issue as much as the area of SF bordering the Pacific Ocean itself. Nothing between here and Asia but a few thousand miles of ocean.

      The Western Richmond and Sunset districts would get hit hard, but those areas aren't completely flat. How high is a big tsunami?

      • jesus_x says:

        An earthquake-spawned tsunami is generally thought to be a maximum of 30 feet high, as the Indian Ocean tsunami was, although I would not be surprised if a super massive earthquake could spawn one of 40-45 feet. A tsunami caused by a landslide however is limited only to the amount of water displaced by the landslide and accompanying air cavity. If the western face of the Island of La Palma gives way, the East Coast is in for a tsunami of possibly hundreds of feet high. I am not aware of any landslide threats in the pacific, but watch out if a Hawaiian island blows up.

    • jabberwokky says:

      I'll be a total git here and not cite sources, but I'm pretty durn sure that a bay with a narrow mouth is a very bad thing for tsunamis. 196x's tsunami did much more damage because it hit a bay that focused it.

      Now having said that, I have no idea if the San Francisco bay would focus the waves... and unless you're looking at underwater terrain maps, I doubt an average LJer has any business making a prediction. But I do know that bays have, in the past, made the effects far worse, rather than better.

      • daikon says:

        Everything ive heard in the news here has suggested the bay would scramble the tsunami as it passes through the golden gate, but this wouldnt be particularly helpful, because it would still roil the bay enough to cause a lot of pier/dock/ship damage as stuff is tossed around randomly.

        • flaede says:

          My 2 cents. I believe what happens depends on the angle the waves hit at. If it's dead on, the bay would narrow the focus, not "scramble" it.
          think air moving through a trumpet vs. air through the front door? which one has more force? Up here in canada we have a prety famous tidal phenomenon based on that kind of focusing effect.

      • jesus_x says:

        Ahh, but I am neither average, nor an LJer. :)

  2. j_b says:

    http://www.abag.ca.gov/bayarea/eqmaps/tsunami/tsunami.html evacuation maps don't have details about how far the waves would go, but it seems they only want to evacuate a few blocks worth of SF. Perhaps the hilly terrain would stop it from flooding inwards very far?

    "These tsunami evacuation planning maps for the ocean side of San Francisco and San Mateo counties are based on modeling of potential earthquake sources and hypothetical extreme undersea, near-shore landslide sources. Maximum run-up to a specific contour was determined to be reasonable.This contour is 12.8 meters (42 feet) in these two counties."

  3. ioerror says:

    What kind of Pacific tsunami?

    Are we talking about an impact from space, part of the big island falling into the sea or an earth quake?

    I was under the impression that there are not any fault lines off the west coast that could cause a tsunami.

  4. daikon says:

    Actually, the general consensus among experts called for the obligatory post remote-disaster "could it happen here" news segments all seemed to agree wed lose about 8-9 blocks of the Outer Sunset immediately adjacent to Ocean Beach, with less destruction in the Richmond because the cliffs become progressively higher as you go north.

    Echo effects of the tsunami flowing into the bay could probably cause a lot of pier/dock damage not so much from flooding, but from roiling the water enough to slam berthed ships around.

  5. jkonrath says:

    There's a short article about this in the current Time:


  6. http://www.noaanews.noaa.gov/video/tsunami-worldpropagation2004.mov

    There's loads of stuff in it that never would have occurred to me, but makes sense when you see it. The way the waves track undersea ridges for example, or the interference effects when they wrap around the world.

    Found at http://www.noaanews.noaa.gov/stories2005/s2365.htm - which has it in multiple formats if Quicktime doesn't work for you.

  7. I'll just take this moment to gloat about my house in Bernal Heights, 250 feet above sea level.

    • jesus_x says:

      The 58 Lituya Bay tsunami in Alaska sent water flying over 1,700 feet up the mountain side. If Hawaii blows, I'll sit here gloating about my apartment in Pennsylvania, 1,400 feet above sea level, and 3,000 miles from the Pacific coast. :)

  8. There was recently this article in the SF Chronicle talking about Tsunamis and the SF Bay, but only in passing.

    What I did find interesting was the graphic they used showing the potentially affected areas of the Richmond and Sunset Districts.

  9. webserf says:

    A table of wave heights for the 1964 tsunamis that hit the US West Coast can be found here: http://wcatwc.arh.noaa.gov/web_tsus/19640328/runups.htm

  10. arsvita says:

    I used to own a condo at Hills Plaza (Folsom & Spear) and part of the disclosure packet stated that I was in a "Tsunami Hazard Innundation Zone."

    Since I lived on the 17th floor facing away from the Bay, I wasn't too worried, though I wasn't looking forward to getting all the saltwater out of my car.