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.
You know, I can imagine someone wanting to develop property over a fault line, but I canât 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?
I can tell ya one thing: Iâd love to be the guy getting commission for selling them earthquake insurance.
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.
Iâve watched this issue discussed by Angelenos, and it often results in a lot of shouting from people who donât understand basic seismology, donât understand the Alquist-Priolo Act, and/or donât 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. Itâs 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 buildingâs foundation directly straddles the fault such that, when the quake occurs, half the buildingâs foundation moves one way, while the other half moves the other way - well, thatâs basically going to destroy the building.
Any building. Short, tall, well-built, poorly-built â doesnât matter. Ripping a building in half tends to destroy it.
Thus the Alquist-Priolo law, which requires State geologists to define approximate zones near âactiveâ faults. (i.e., faults that show evidence of movement during the Holocene â 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.
Itâs 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 â maybe every 3k yrs on average â to make a Rilly Big Quake of ~ Mag 7.
But bear in mind that âperiodicityâ 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 thereâs some chance these events could happen tomorrow; but the odds are also reasonably good that they wonât happen in our lifetimes.
Historically speaking, the majority of Californiaâs damaging quakes have occurred on faults that no one was aware of until the quake happened. Even with todayâs advanced techniques, this will probably continue to be true,
Itâs a very⌠odd⌠sort of risk analysis.
So, if somebody gets hurt or dies, then whose fault is it?
âWeâll just buy no-fault insurance, and everything will be fine! Thatâs what that means, right?â
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, Iâm sure the seismologists understand what a black swan is, and Iâm also sure developers and legislators do not. If I was a gambling manâŚ
No, itâs not impossible - you just have to dig a very deep trench. Which they did. But the State geologist didnât get a look at it, and is depending on inferences from surface surveys
The developerâs geologists say, yeah, thereâs probably a deeper fault under the site, but itâs 150k yrs old and thus âinactive.â
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. (-:
Surprised that they can get insurance or financing.
Those geologists; always going off about âthis site is unsafe!â and âbuilding a skyscraper here will endanger lives!â Theyâre starting to sound like a broken record(-shaped building).
I also hope this isnât the potential construction that was going to potentially damage the Capitol Studios unique underground echo chambers.
Wellington is sensible enough to own up in advance of âthe big oneâ.
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)
I always thought Zone D stood for âDoomedâ? 
I can absolutely tell you that people here are that stupid, and would definitely not think about it twice. Sure, thereâs going to be the occasional person who thinks about it and decides not to live there, but for every smart one, thereâs 5000 thinking âyeah, itâs a bit expensive, but itâs new, and the gym is super coolâ.
So the City or State authorities canât say âNo you canât build this. Just no.â?
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.
As long as there wasnât an Indian Burial Ground.
This topic was automatically closed after 5 days. New replies are no longer allowed.
