Might be true, might not, but as a lifelong Angelen@, I get really nervous when the train goes underground for any period of time. I don’t trust the earth to stay put, and I find the idea of being buried in the Red Line…disconcerting.
Elon Musk has a long history of pontificating on topics he knows little about. He shows no more assurance of being an expert on geophysics and seismology than he does about machine intelligence.
Earthquakes cause the greatest displacement on the ground surface for the simple reason that the surface is an essentially unconstrained boundary that is free to undulate. That doesn’t mean that structures underground don’t experience the energy of the seismic event or cannot suffer shearing stresses or collapse. As Sloe Moe notes, even if a tunnel doesn’t collapse the redistribution of stress can cause leakage or otherwise compromise the integrity od the tunnel. Aboveground transportation structures like bridges and overpasses can also collapse, or course, but this is largely due to older construction methods that do not incorporate earthquake protection. Tunnels have a number of other difficulties but the biggest reason we don’t build extensive networks of underground tunnels for transportation except in cities with extremely high population densities is because they are really expensive to build and maintain.
Stranger
Yes, that’s true, but if someone asks if earthquakes are a big deal for tunnels and I reply “Not especially. It’s primarily a problem for surface structures” I think it’s pretty damn nitpicking to call me a liar because the rate of tunnel failure isn’t 0.00%.
I’ve actually done a small amount of analysis on tunnels professionally.
Not super current, but http://cdn.wspgroup.com/8kzmue/seismic-design-of-tunnels-a-simple-state-of-the-art-design-approach.pdf is a good guide.
I didn’t say that he was lying (then, I did say he would be lying if he said “earthquake proof”). I said he was speaking bullshit, which is not the same as lying.
And yay, *you’ve *done analysis on tunnels. I’ve been 1km underground in hard rock when an earthquake struck, so I will say again - “essentially a surface phenomenon” is bullshit.
I think he just wasn’t careful with his terms. He must have meant the adverse effects of an earthquake are seen mainly at the surface.
No dispute there. But it’s also kind of tautological - the adverse effects are mostly seen at the surface because the surface is where everything is.
The thing is, Musk’s statements are based off a sound principle - tunnels in hard rock are more resistant to earthquakes - greatly so. But he’s taking that principle and overselling it, and using obfuscatory language to do so.
I mean I’m one of Musk’s biggest detractors (I will actually give him credit for many of his genuine achievements, but I think he lies and exaggerates a lot and I think Tesla is a very overvalued company because of these effective lies and exaggerations); but I don’t find a huge issue with what he said. I listen to the Joe Rogan podcast occasionally and I listened to this episode in full.
For the actual venue and typical listeners of Rogan’s podcast I don’t think Musk said anything here that was meaningfully ridiculous enough to warrant getting hot and bothered about it. He doesn’t present himself as a civil engineer in the interview or an expert in tunnel construction, he even later talks about the engineers who work for him that are more hands on with it–he likely simply paraphrased stuff they’ve said to him, and I think he did so with enough fidelity to convey the essential “idea” in a manner that’s fine for the audience of the Joe Rogan Experience. This wasn’t an interview with a news outlet, wasn’t a pitch to investors, wasn’t communications to city officials to help get permits or etc. The conversation wasn’t really about earthquakes but more how Elon gets his hands into so many pies.
No-one’s “hot and bothered” by it. Bullshit is a technical term, not a sign of upset.
And in most major earthquakes, you don’t hear of major collapses of pipes - sewer, water, gas, etc. - except at shear zones and where they enter buildings. Presumably the same effect. I assume if the underground cavity size were significant, there would be a risk that the shaking could cause a roof collapse - the edges of the cavity present the same boundary condition hazard as a surface; but generally there is not the same amount of stress on a tunnel as on a building in open air where the shaking is unconstrained.
Broken gas and water mains are common in SoCal quakes. E.g., the Northridge quake of 1994 broke some gas mains under roads some of which caught fire (last par of the section in the link). The video footage is … interesting. The broken water mains caused problems for firefighters putting out numerous fires.
Mains are basically near-surface objects so the surface effects are still quite noticeable. E.g., differential shifting of soil over short distances.
What about the difference of timescales between earthquakes and tunnel-formations?
Prepare for assumptions:
Earthquakes are an event on a timescale of dozens to hundreds of years(?) New tunnels being formed happen on a timescale of centuries to millennia(?)
So, would it reasonable to assume any earthquake-susceptible tunnel would be weeded out relatively early in it’s formation; leaving only the earthquake-impervious tunnels to continue growing?
“Liquification” - that’s the term I was looking for. I’ve heard that the delta mud in Vancouver/Richmond may be subject to liquification in an earthquake. Wouldn’t that affect tunnels going through the mud?
I remember that the Loma Prieta earthquake didn’t damage the BART system of the Bay Area (though the Bay Bridge was severed), but I don’t know if BART actually goes through mud when it goes under the bay.
If you mean was it bored underneath the bay, no it wasn’t. The Transbay Tube is an Immersed Tube tunnel - sections were fabricated on land, then transported out to the bay, sunk into place on the bottom, and reinforced with fill around them.
It is worth noting that during the Loma Prieta Quake a BART train was actually in the tube - the driver didn’t notice anything, but was ordered to stop in accordance with established procedure for earthquakes. The tube was reopened in 6 hours, and the entire BART system resumed normal service in 12. Good thing, too, as it took over a month to fix the Bay Bridge (which was a much shorter time than originally estimated).