Are tunnels earthquake-resistant?

So a few days ago Elon Musk went on a podcast where at one point he explains that tunnels are earthquake proof, and using a submarine under the ocean during a storm as a sort of analogy. Now I’ve been wondering about this, to what degree would a tunnel system really be earthquake resistant? What kind of soil or ground would be needed for the tunnel to be earthquake resistant, and how sure can we be it’s safe. Now just based on some assumptions, I’m guessing a regular tunnel through a mountain or something isn’t earthquake proof, and instead it’s tunnels that go under hard ground are (which would be the case with a 3D road). Where could these tunnels function as earthquake resistant, and is it even the case? I doubt elon was bullshitting, although I don’t really understand the whole situation here maybe someone can give me some insight.

Edit: Should have specified in the title I’m talking about “underground tunnels”.

What material is earthquake-proof, both under and above ground, is hard virgin rock free of faults, fractures, weathering and alteration. Having that as your foundation on the surface, or country rock at underground, is always a good investment.

But, what you are asking is not about the rock but the man-made structure. If the tunnel is driven through good rock underground then the likelihood of damage is small. But a tunnel has vulnerable parts. The entrance from outside, for instance, where you have a layer or soil or altered rock, is at risk. Also, your tunnel interior might have portions that are fractured, or vulnerable to shifting and roof collapse.

And hard rock is not a guaranty of complete safety. There was this suspension bridge in Japan. Its columns were driven through hard rock. But there was an active fault running across it and following an earthquake, one half of the bridge was dis-aligned by 1 meter.

You can read a nice review on the subject here.

An early report came to these conclusions:
[li]Collapse of tunnels from shaking occurs only under extreme conditions.[/li][li]No damage occurred when PGAs were lower than 0.19 g and/or PGVs were lower than 0.2 m/s.[/li][li]Minor to moderate damage occurred when PGAs were up to 0.5 g and PGVs up to 0.9 m/s.[/li][li]Moderate to heavy damage occurred when PGAs were larger than 0.5 g.[/li][li]Tunnel collapse only occurred associated with movement of an intersected fault.[/li][li]Tunnels are much safer than above ground structures for any given event.[/li][/ul]

Subsequent reports have largely agreed with these findings, with the caveat that the behavior is more complex than originally thought (no surprise there).

The submarine analogy is a loose one, but people who build tunnels in seismically active areas make largely the same argument:

So it is generally true that tunnels are pretty safe during an earthquake, with some caveats.

Elon Musk is a fucking idiot. Underground during a quake is nothing like underwater during a storm (I’ve been underground during a small quake). But he’s not exactly wrong, either. Tunnels are more resistant to earthquakes than above-ground structures (same as** Dr. Strangelove**'s first link). But the key word there is resistant. Not immune. If he actually said “Earthquake proof”, he’s a liar.

Let me follow up for you with this question then.

Which is safer: A house above ground, or a house underground (both in ideal conditions)?

Edit: My response actually triggered a more serious question. Would humanity fare better underground than under water? Maybe going underground will be better than going under the ocean? Which eventually I believe it’s inevitable we’ll start living underground/under ocean and on other planets, if nothing disastrous happens that is.

Musk never said they were earthquake proof. He just says that tunnels are very safe in an earthquake. The analogy is imperfect but completely reasonable for a lay audience.


We’d be better off underground than under water.

The OP said he did, and I’m not going to watch a video to see what he actually said. Is there a transcript?

The entire referenced bit is just this:

He goes on to describe the specific tunnel that the Boring Company is designing (not tunnels in general).

Generally underground; earth and rock mostly just sit there, while water not only seeps into even tiny gaps but seawater specifically is pretty corrosive stuff to most of our technology.

Yeah, that bit I highlighted is pure bullshit. And I speak from experience.

Also, I hope he actually said “phenomenon” and that was just transcription error :smiley:

I’m grossly incompetent in my display of information on this site, I tend to just go full retarded and project every ignorance I have so (as expected) dopers can correct and educate me. Elon most likely did not say that word for word, I was simply expressing wherever I said “earthquake proof” that they were implied heavily earthquake resistant. Sorry for the misunderstanding due to word choice, I should have been more careful when quoting someone who actually knows what they’re talking about.

The LA Metro has this article about the effect of earthquakes on subways.

There is a chart showing the effects of major earthquakes on subway systems around the world. The effects were minimal.

e.g. Chile 2010 - earthquake magnitude 8.8 - subway running the next day, with some damage at entrances to stations.

They generally don’t build tunnels across fault lines. ie part of the tunnel moves one way and another part moves a different way.

Also generally speaking, IIRC buildings get damaged by earthquakes when they are too rigid and brittle to handle the vibration. Large skyscrapers, counterintuitively, are mostly fairly safe from earthquakes because they are already built to flex and sway in high winds.
I would imagine a tunnel is relatively safe for the same reason they tell you to hide in the door frame during an earthquake. The tunnel is already designed to resist a massive load on top of it.
Of course…I can’t speak for a landslide covering one or both ends of the tunnel.

I’m not sure why your link invalidates the fact that vast majority of earthquake effects are surface effects. As a civil engineer I don’t have any issue with what Musk said. Neither does any of the literature.

Note that some damage to a tunnel to a quake takes a bit to show up. The lining can be easily cracked and water can start to seep in, for example.

In LA specifically (where Musk wants to bore a couple of tunnels), the possibility of natural gas and oil seeping into a tunnel is a major concern. Earthquakes can readily damage any barriers placed to prevent this. Plus there are minor faults all over the place increasing the problem.

Doesn’t it depend in part on what the tunnel is going through? For instance, there are tunnels in Vancouver which go under ocean inlets, where the ground is not rock but delta muds. I’ve read that that kind of sub-surface is very vulnerable to certain types of earthquakes, leading to major shifts of the sub-surface itself. Wouldn’t that be different than a tunnel through solid rock?

Given a long enough time frame, perhaps. For the foreseeable future, there’s still a whole lot of open real estate on the earth’s surface without going full Morlock. The interiors of South America and Africa, most of Canada, the western United States, most of Australia, huge portions of Asia, etc are all lightly populated. Granted, living in the center of Australia is no picnic, but I’m not sure if it’s harder than creating subterranean lairs for a hundred million people.

I am not a geologist or an architect or engineer, but educated guess:

Surface buildings fail in two ways - the foundation sinks (like SF or Mexico City) so the building fails or topples; or, the shaking and building inertia cause the joints in the building to fail as it moves, so typically where beams meet posts the joint breaks (or the beam, or the post - especially concrete cracks open) and the structural integrity fails.

A tunnel would be immune to the latter, generally. What happens with the former- depends how serious the liquification/softening of the ground is that it is immersed in. In relatively solid ground, probably not a problem. Another issue is “wave” action when pressure waves bounce off surrounding bedrock and reinforce, as happened in Mexico City, built on a swamp, or the waterfront landfill in San Fran. However, likely the effects are most pronounces at the surface, where the ground has freedom to move in response to pressure waves.

My emphasis:

It doesn’t. But that’s not what Musk said.

It’s beyond obvious from context that he’s talking about the effects. In fact, it’s impossible that he’s talking about the origins because other than landslide caused earthquakes, all earthquakes originate beneath the surface. If you want to be a hyper-pedant in order to score internet points against Elon Musk, I guess congratulations.