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Time for a San Francisco Bay tsunami truther thread. A lot of people in the East Bay got a scare today, but in fact it's hard to create any tsunami scenario that does more than get people's socks wet. Remember that the bay is very, very shallow, thanks to the 1848 Gold Rush.

8:30 PM · Dec 5, 2024

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Pinboard

@Pinboard

Dec 5

The deepest part of the Bay is right under the Golden Gate. Any tsunami that enters the bay will rapidly weaken. Here's a figure from a 2006 paper that modeled the worst-case scenario, an Aleutian earthquake (Aleutian III). Notice the attenuation by the time it hits Richmond.

(Note that Inner and Outer Richmond in that table don't refer to the San Francisco neighborhoods with those names, but to Richmond in the East Bay. For tsunami purposes you can think of it as the moral equivalent of Berkeley.)

What it comes down to is that there's just not a lot of water in SF bay for a tsunami to work with, and the Golden Gate is too narrow to rapidly admit a big inflow. So next time you get a tsunami warning in Berkeley, just put on shoes with slightly thicker soles and relax.

If you live in the Outer Sunset (the westernmost part of the SF penninsula), of course it's a whole other ball game. An Outer Sunset tsunami can and will wreck your shit. But no need to be so scared of tsunami waves if you're sitting in the cross-bay tunnel or in Alameda.

2006 paper on modeling tsunami hazards here (with a focus on risks to the oil terminals in the East Bay) earthjay.com/earthquakes/20

If you're wondering what the Gold Rush has to do with Bay Area hydrology, the 49'ers used high-pressure hoses to mine gold in the Sierra Nevada, silting up the bay so badly the effects persist to this day. There was even serious talk of filling the Bay in the 50s.

Anyway use Pinboard.

My bad; I said upthread the 49'ers used hydraulic mining in search of gold, but the hydraulic era apparently started in the 1860's. It lasted until a fed-up state government banned it a few decades later, after adventures like a flood that filled the Central Valley.

How did the ‘48 goals rush make the bay shallow?

Massive silt runoff from hydraulic mining (high-pressure hoses) in the Sierra Nevada

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Lisa AI: Art, Magic Avatar

@lisa_aiart

Prompt Guide 101 Tell a Story! Create a story to bring a scene to life. For example, instead of saying 'a beach', say 'a deserted beach at sunset relaxing to the sound of the waves'

this sounds plausible I am willing to believe it.

I am willing to drown under the sea waves believing it!

I was wondering why, when I zoomed in on all of the diagrams and looked at the affected area... It was always so shallow? It didn't seem to go deep into SF, nor into the South Bay or either side. It seemed to go to the hills across Berkeley which makes sense, but it seemed

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Shen Yun

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Shen Yun 2025 in Northern California

I think your conclusion is right, but for the wrong reason… AIUI shallow water near shore *increases* tsunami amplitude due to shoaling - deeper water is better, not worse. But as you say below, Golden Gate is so narrow that most of the wave reflects and never enters the bay

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