By way of the California Emergency Management Agency, California Geological Survey, and University of Southern California: San Francisco’s Tsunami Inundation Map.
The inundation map has been compiled with best currently available scientific information. The [red] inundation line represents the maximum considered tsunami runup from a number of extreme, yet realistic, tsunami sources. Tsunamis are rare events; due to a lack of known occurrences in the historical record, this map includes no information about the probability of any tsunami affecting any area within a specific period of time.
Pink is potentially problematic. Now about that development of Treasure Island…
∙ Tsunami Inundation Map for Emergency Planning: San Francisco [ca.gov]
∙ Treasure Island: Sold To The Bidder Across The Bay For $105M (Plus) [SocketSite]
LOL Treasure Island
Ahhh… No wonder there’s a big development push to water taxis and ferry service! It’s now much much clearer.
I’m no geologist, but doesn’t the direction of the wave play a huge role in where/how much is inundated by a tsunami? I seem to recall that the direction the wave was traveling was a big reason why Somalia was affected by the big tsunami but places closer to the actual earthquake weren’t since the tsunami’s energy was mostly displaced east/west rather than north/south
And if that’s the case, WTF with the eastern side of San Francisco being all pink? Is that assuming that the earthquake happens directly under the San Francisco Bay? But there aren’t any faults passing under the Bay, are there? After all, it’s not the earthquake itself that causes tsunamis but underwater displacement.
So confused. Maybe someone who is an actual scientist could explain.
Two surprises :
1. the east half of the city does not seem to be better protected than the Pacific frontage. I’d think that the Golden Gate would throttle any tsunami surge.
2. so much of the Marina is affected.
Nevermind, found my own answer. Apparently sometimes “diffraction” happens with tsunamis, as the wave passes around an obstacle. For instance, per Wikipedia the west coast of India was affected by the tsunami even though it wasn’t directly in the path of the wave.
[i]so much of the Marina is affected.[/i]
The Marina, having been built on fill, is pretty flat. The west side shoreline is for the most part natural, with either bluffs or hills going right up to the water.
Also, judging by the direction of the swells at Ft Point, I could see how a tsunami would affect the Marina (the diffraction effect mentioned by anonyman would likely play a role as well).
Why would anyone be surprised that the Marina is vulnerable? A tsunami would pass right through the Golden Gate and wash up into the Marina. In fact, the Golden Gate may magnify the effect of a tsumani by forcing the energy through a tighter slot.
Tsunamis are rare and may never happen to hit SF head on. (Note that even waterfront and low lying property around Lake Tahoe is also vulnerable to tsunamis, and geogolgic record shows definitive evidence of sizable tsunamis in the lake from major seismic events in the past 10,000 years that have triggered large underwater landslides.) There was an article in the Chron about this a couple years ago). But the much bigger concern which is a more immediate certainty is sea level rise, which would potentially affect much more land area than tsunamis, dependent on the amount of sea level rise. (Of course, the tsunami map above is only based on today’s sea level. As it rises, more area will be subject to tsunami risk). While mean sea level may rise by one meter in the next 100 years, high tide and storm surges that only go higher from there will have much more certain and regular effect than any tsunami, and would inundate all of Mission Bay, and big parts of SOMA, Central Waterfront, Marina, and could even reach into the Mission.
Then of course, Pacifica is quickly eroding into the Ocean.
Why would anyone be surprised that the Marina is vulnerable? A tsunami would pass right through the Golden Gate and wash up into the Marina. In fact, the Golden Gate may magnify the effect of a tsumani by forcing the energy through a tighter slot.
Tsunamis are rare and may never happen to hit SF head on. (Note that even waterfront and low lying property around Lake Tahoe is also vulnerable to tsunamis, and geogolgic record shows definitive evidence of sizable tsunamis in the lake from major seismic events in the past 10,000 years that have triggered large underwater landslides.) There was an article in the Chron about this a couple years ago). But the much bigger concern which is a more immediate certainty is sea level rise, which would potentially affect much more land area than tsunamis, dependent on the amount of sea level rise. (Of course, the tsunami map above is only based on today’s sea level. As it rises, more area will be subject to tsunami risk). While mean sea level may rise by one meter in the next 100 years, high tide and storm surges that only go higher from there will have much more certain and regular effect than any tsunami, and would inundate significant portions of the east side of the City.
Then of course, Pacifica is quickly eroding into the Ocean.
A tsunami is not like a regular wave, in which the water is simply shifted from the hollow to the crest, making for a big wave which crashes on the shore then recedes. Rather, there is a rise of the entire water level, as if you had tipped a basin half-full of water so that all the water rushed to the other side. Water would pile up several hundred feet at the Golden Gate, where the land is at least that high. This huge wall of piled up water would then pour through the Golden Gate and raise the level throughout the bay and flood everything there, then slowly leak back out of the Golden Gate. There would be no crashing waves within the bay. Rather, the level would just slowly rise and rise and rise until it made a mess. Sort of like a backed up toilet: “please make it stop before it reaches the rim, please make it stop, oh no, it’s overflowing!”
I feel so much safer with this knowledge. Thanks to the government agencies for spending my tax dollars on such an important project.
If this were the Bush years, we’d immediately give Haliburton $1B to build a garage door under the golden gate bridge to seal off the ocean in the event of a tsunami and protect us from this terrifying risk. But alas, the communists currently in power have given that money to *their* friends, the bankers and the unions, and so we have nothing for preparedness.
If a tsunami arrives, we’ll just borrow a bunch of money from the bankers and hand it to union guys with shovels and brooms earning $85 per hour to clean up the mess.
Oh tipster, how quickly you forget that it was Bush and Paulson that first started giving the money to the bankers. But I guess you have never let reality stop you from your quips before, why start now.
Glad to see BayCrest is okay from the Tsunami map perspective … now if we can just knock some sense into the High-Speed Rail Authority regarding laying tracks down the middle of Watermark and my home at BayCrest Towers. 😉
no, no, no, the water will not “pile up several hundred feet at the Golden Gate.” that is not how the physics of tsunamis work (unless you are very close to the actual quake epicenter). thousands of miles away the behavior is very different, depending more on the underwater topography than even the coastline configuration. the underwater topography of the Golden Gate is very complex, with the shallow Potato Patch Bar arcing several miles offshore and then a very deep channel at the Gate itself. the State survey did not actually attempt to calculate the detailed tsunami physics of this situation. and it also assumed the event happens at mean high tide – a worst case.
Actually, being close to the tsunami epicenter (at sea) you are unlikely to detect much of a change in sea level. It’s when the massive amount of energy from the tsunami wave reaches the shore that stuff gets crazy.
Think about how much energy is required to accelerate a mile-deep column of water up vertically a few feet (i.e. what happens in a big offshore quake). That energy propagates through the ocean in a wave, and when that wave reaches the shore, the manifestation in water that’s only a few feet deep is very dramatic.
Still, “several hundred feet” is a gross exaggeration of tsunami height. The largest tsunami on record to ever strike California was in Crescent City in 1964 and reached about 20 feet. It would be a rare event indeed to see that big a wall of water smack into SF.
Of course, anything could happen. But in SF I’d be more worried about earthquakes themselves than tsunamis. Ah, what an awesome city we live in. 🙂