The relative safety of large buildings during massive earthquakes
August 7, 2013 10:48 AM   Subscribe

How many people during the Tohoku 3/11 earthquake actually died from the earthquake itself, and not the tsunami? Also subtract elderly heart attacks, people being fatally crushed under bookshelves/the like, and the collapse of rickety old traditional houses that would have been knocked out during a smaller quake too.

Well, that sucked. 2:30 AM and I just woke up from a nightmare where my wife and I were trapped at the top of Tokyo Tower during a massive, massive earthquake. Not that ridiculous a situation, given that we both live in Tokyo.
Is there any significant data about what happens in similarly massive but modern structures in the event of a 6-7+ earthquake? Tokyo Skytree? Landmark Tower?
I know that the building codes for earthquake resistance are among the strictest in the world here, but am curious if there have been examples of skyscraper/tower collapse from anywhere else in the world. I remember seeing a documentary about the countermeasures in place for that building in Dubai, and it included a gyroscope/pendulum of some sort at the very top; what would it take to knock something like that over? Are so-called "pancake collapses" as rare as wikipedia would have me believe as long as I'm in a building of Japanese and not Chinese provenance?
How good, exactly, is our architecture in this regard?
During the Fukushima earthquake, how many people actually died of collapsed buildings of modern construction? The lion's share of fatalities, according to the narrative I heard, were from people too old or daft to heed the warnings and subsequently getting swallowed up by the tidal wave.
posted by GoingToShopping to Science & Nature (4 answers total) 1 user marked this as a favorite
Best answer: Here's an interesting (to weird ole me) article about the nature of the deaths.

The sad fact is, there's probably never going to be a specific count. Here's a quote from the article:

It will never be known how many died due to the earthquake, as separated from the tsunami; however the CATDAT analysis, the autopsies give us an indicator that we can expect that about 1.4% of the 4.2% crushed were probably in earthquake collapsed houses.

Here's the thing. The modern buildings are probably as good as it gets. If the earth really shakes, we're all out of luck.

The more traditional houses with the tile roofs, those pancake pretty frequently during siesmic actiity.

I was in the Loma Preita Earthquake in California, and I used to be the resource for Disaster Recovery at BellSouth (ask me about Hurricanes, Tornadoes, Earthquakes, etc. I've got an answer.) I maintain the worst thing to happen in the future is movement on the New Madrid Fault. Memphis doesn't believe me though.

The good news is that Japan is very pro-active in addressing infrastructure (as opposed to the US where shit just falls down.)

You should have a plan for disaster. One thing worth knowing, even if the voice phone system is down, you should be able to get text message through.
posted by Ruthless Bunny at 11:58 AM on August 7, 2013 [1 favorite]

Best answer: Civil engineer here (although not a structural or seismic specialist) and modern buildings are quite good at resisting earthquake damage as long as they are built to code. Japan has both things covered as they have the best earthquake codes and readiness in the world and they have a professional bureaucracy to inspect things to make sure they are meeting those codes (And my understanding of the philosophy in Japan is violating laws/ordinances is JUST NOT DONE there). I don't have a source to point you to but i remember readign that the loss of life (and even property damage) from the earthquake outside of the tsunami zone was very minimal considering the size of the quake.

In order of buildings best able to withstand earthquakes:

wood framed residential housing on pier and beam foundations, closely followed by residential housing on any other foundation. (residential building codes result in very overbuilt houses with lots of flexibility from the wood structure and the simple joints used)-I don't know how common this kind of building is in japan (and if you have a heavy roof on it like tile it isn't nearly as safe)

Steel framed structures (flexible but usually not as overbuilt as wood frame housing). This would be stuff like the Empire State Building and such.

Reinforced concrete is also pretty good if it was built or retrofitted to withstand earthquakes. The problem with this stuff is the concrete and steel reinforcement work together to give the building strength-concrete in compression and steel in tension. During an earthquake the structural members in the building get loading from weird directions that put the concrete in tension and makes it break, than rapidly switch back to compression and the now broken concrete 'spalls' or comes flying apart and isn't there to support the load anymore. This is pretty much the 'pancake' collapse you fear (and it is scary). Modern construction is built with this in mind, uses a different kind of concrete, different method of steel reinforcement and can withstand the shaking. Older stuff can be retrofitted to contain the spalling and also be pretty safe. when poorly done you get the nightmares stuff from Haiti and Turkey with widespread building collapse. I bet it isn't hard to find the building manager and ask them about this issue.

then the worst kind of building is unreinforced concrete or masonry buildings. Think about shaking apart a Lego set-it pretty much works like that in the real world also.
posted by bartonlong at 3:35 PM on August 7, 2013 [3 favorites]

There were a couple of videos on CNN's iReport page of the earthquake. They were fascinating.

One was of a guy in a park. The ground wasn't shaking, it was just undulating at like 1 hz. Up six inches, down six inches. Terrifying, but not at all violent.

The other one was of people in an office building. The thing was shaking like crazy. Pictures rattling off of walls, computers falling off of desks, etc. It was a much faster frequency, but at a lower amplitude. The biggest (apparent) danger was of people going berserk, any possibly getting whacked on the head by something falling. The building took the big, slow waves and converted the energy into faster, but much shallower and less dangerous ones.

Larger buildings built for earthquakes take a lot of things like this into account when they are designing it. Every structure has a resonant frequency. If the earthquake happens to be at the building's frequency, it will tear itself apart. So what designers do is place heavy masses near the top of the building to change the frequency at which it resonates to something that is not expected during an earthquake. The plaster might crumble and the windows might crack, but it won't fall down.
posted by gjc at 5:18 PM on August 7, 2013 [2 favorites]

There are a number of things at work here, but the basic one is that most residential buildings anywhere are pretty much just resting on the ground. There usually isn't much done to resist lateral forces such as in many earthquakes, and so it's just like the ground moves out from under the structure, in a manner of speaking, and the structure no longer has integrity and collapses.

Skyscrapers, however, are almost universally built on top of some sort of deep pier structure, reaching into bedrock some places, or just generally piles sunk into the mud/muck. Then the steel structure has fastenings that hold it in place when lateral forces strike, and instead of one level pulling out from under the other, the swaying forces are transmitted up and down the structure in waveforms. Many modern skyscrapers then mitigate these forces using a tuned mass damper near the top -- essentially a way to suck the kinetic energy out of the structure and into an isolated mechanism. They use things such as springs, hydraulics, and even just oil to act as an oppositional force to the earthquake.

It does seem terrifying, but a skyscraper is probably one of the safest structures you can be in during an earthquake. Up toward the top you might lose your lunch in the shaking, but the building is going to wave around a lot and then slowly stabilize.
posted by dhartung at 1:15 AM on August 8, 2013 [1 favorite]

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