L.A. plans to build massive skyscrapers over fault line


#1

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#2

There is a positive side. Something to look forward to.

There will be an interesting episode of Seconds to Disaster, and some nice chapters in engineering books.


#3

You know, I can imagine someone wanting to develop property over a fault line, but I can’t imagine anyone setting out to live in a skyscraper built over a fault line. Like, how much of a discount would they have to be selling units at for people to want to take that risk?


#4

I can tell ya one thing: I’d love to be the guy getting commission for selling them earthquake insurance.


#5

Where I live, the city prevented people from building in a flood plain along side a waterway. Someone really wanted to, so they fought the city in court for a long time to get approval and they finally won it (under the stipulation that they could only build a garage, because after all it was going to eventually flood). When it finally flooded, the owners sued the city for allowing them to build the structure, because they had been storing valuable things in the garage space. I imagine something similar will happen here, only the result will involve collapsed buildings and a bunch of dead people.


#6

I’ve watched this issue discussed by Angelenos, and it often results in a lot of shouting from people who don’t understand basic seismology, don’t understand the Alquist-Priolo Act, and/or don’t know much about seismic structural engineering.

Just to head off some of the usual sources of confusion:

This is NOT about how CLOSE to the fault the building might be. It’s about whether or not the building directly straddles the fault.

The difference is vast - a modern, well-built high-rise tower sitting right next to the fault should (should!) survive the Maximum Credible Quake on this fault with no real trouble. And the difference between being right next to the fault and being five blocks away is almost irrelevant. Distance counts, but not that much.

OTOH, if the building’s foundation directly straddles the fault such that, when the quake occurs, half the building’s foundation moves one way, while the other half moves the other way - well, that’s basically going to destroy the building.

Any building. Short, tall, well-built, poorly-built — doesn’t matter. Ripping a building in half tends to destroy it.

Thus the Alquist-Priolo law, which requires State geologists to define approximate zones near ‘active’ faults. (i.e., faults that show evidence of movement during the Holocene — the last ~11k years.)

Anyone wanting to build inside these zones is required to do the geological studies necessary to determine the precise location of the fault (which is often, as here, buried under more recent sediments emplaced since the last rupture).

The idea is to prevent buildings from being ripped in half because they straddle a fault.

Now, the Hollywood fault has ripped during the Holocene - most guesses put the most recent event ca. 700 yrs ago, and the slip rate suggests a periodicity of ca. 1600 yrs. for a Maximum Credible Quake of mid-5 to mid-6 magnitude.

It’s also possible that the Hollywood Fault, the Raymond Fault to its east, and the Malibu fault to its west, all gang up from time to time — maybe every 3k yrs on average — to make a Rilly Big Quake of ~ Mag 7.

But bear in mind that ‘periodicity’ is the long term average interval, not a regular interval.

Geologically speaking, five times in a thousand years followed by four thousand years of silence is a 1000-yr recurrence rate.

So there’s some chance these events could happen tomorrow; but the odds are also reasonably good that they won’t happen in our lifetimes.

Historically speaking, the majority of California’s damaging quakes have occurred on faults that no one was aware of until the quake happened. Even with today’s advanced techniques, this will probably continue to be true,

It’s a very… odd… sort of risk analysis.


#7

So, if somebody gets hurt or dies, then whose fault is it?


#8

“We’ll just buy no-fault insurance, and everything will be fine! That’s what that means, right?”


#9

But as you point out, it is impossible to pinpoint the location of the fault, so the problem falls back to how close to the best estimate.

As for surviving the Maximum Credible Quake, I’m sure the seismologists understand what a black swan is, and I’m also sure developers and legislators do not. If I was a gambling man…


#10

No, it’s not impossible - you just have to dig a very deep trench. Which they did. But the State geologist didn’t get a look at it, and is depending on inferences from surface surveys

The developer’s geologists say, yeah, there’s probably a deeper fault under the site, but it’s 150k yrs old and thus ‘inactive.’

I am pleased to see that the city council has required ongoing geological investigations as the footings are dug, with full documentation. A careful look at the footing excavations should settle the question even more clearly than the survey trench

Faults concealed by overburden are not impossible to locate precisely - you just have to dig some deep, long trenches or big holes. (-:


#11

Surprised that they can get insurance or financing.


#12

Those geologists; always going off about “this site is unsafe!” and “building a skyscraper here will endanger lives!” They’re starting to sound like a broken record(-shaped building).


#13

I also hope this isn’t the potential construction that was going to potentially damage the Capitol Studios unique underground echo chambers.


#14

Wellington is sensible enough to own up in advance of ‘the big one’.


#15

Huh, I never knew about that … and I have a somewhat heightened and direct interet in the subject. I live in Zone B (good … I assume?), but work in Zone D (eep)


#16

I always thought Zone D stood for “Doomed”? :smiling_imp:


#17

I can absolutely tell you that people here are that stupid, and would definitely not think about it twice. Sure, there’s going to be the occasional person who thinks about it and decides not to live there, but for every smart one, there’s 5000 thinking “yeah, it’s a bit expensive, but it’s new, and the gym is super cool”.


#18

So the City or State authorities can’t say “No you can’t build this. Just no.”?

The engineers will have reports on what is a 100 year quake, and build to withstand it. But the question here is which report numbers to beleive. The safer numbers or the cheaper numbers.


#19

As long as there wasn’t an Indian Burial Ground.


#20

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