Oakland gets a (small) tsunami


Oakland is fairly safe from tsunamis. Not as safe as San Ramon, but safer than most Pacific ports. First of all, we sit rather far from any dangerous subduction zones. When you track the subduction zones of the Pacific’s “ring of fire,” you get a continuous zone from Chile up to Puerto Vallarta, then jump to Cape Mendocino where the Cascadia subduction zone begins. We’re in between, and huge thrust-type quakes are not tectonically possible here.

A giant quake in Cascadia or the Aleutian Islands subduction zones would send waves down this way, possibly up to 2–3 meters high (this is the height out at sea; as they hit shore they would rise much higher). That’s where our second line of defense comes in: the Golden Gate. Anything coming through there would first be throttled by the narrow strait, then would spread out once it enters the bay. The people who prepared the Alameda County tsunami inundation maps also considered a few local extreme earthquakes that may have components of thrust. These could raise local tsunamis, but not of the horror-inducing size we saw in Japan.

I don’t want to minimize the possibilities, but the Sendai scenario cannot occur here. The harbor, however, is liable to damage even in a modest event, as we saw in Santa Cruz. Ships will bang into docks and each other; a less obvious hazard is that swift currents may pluck ships off their anchors and wash mud into our carefully dredged channels. You won’t want to go down to Jack London Square and watch if there’s a big local quake or a great event in Alaska or Cascadia. But last week would have been OK. Did anyone see the water there?

5 Responses to “Oakland gets a (small) tsunami”

  1. Jafafa Hots Says:

    Here’s a video from Golden Gate Fields of it coming in.

  2. Andrew Says:

    I saw it in the Tribune, but it looks like the Mercury News’s version is longer. The experts that are quoted, Lori Dengler and Eric Geist, are the real thing. I’m pleased that they didn’t baldly contradict me.

    They improved on this post by emphasizing the eastern Aleutians fault segment. If you hear of a magnitude-8 or larger event there, watch out. It would involve Kodiak Island, the Alaska Peninsula, and little towns like Sand Point and King Cove.

  3. Naomi Schiff Says:

    So I presume you saw that discussion in the paper about how the deep water channel could cause a tidal wave to have a particularly heavy effect on the Port of Oakland?


  4. Andrew Says:

    Thanks for linking that. The wavelength of a tsunami is so great (its period is so slow) that to us it behaves more like a temporary rise in sea level–a fast version of the tide. That behavior is how it got its traditional name of “tidal wave,” which unlike most people in geology I have no objection to.

  5. Naomi Schiff Says:

    I guess the person taping this was up in that tall building in E-ville, by the freeway, probably. Interesting to see how it is such a continuous, coherent wave.

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