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This question is fairly self-explanatory. The civilisation in my story is in an earthquake-prone area due to lots of tectonic plates. Could using magic to make their cities levitate and thus not be affected by it be a viable solution?

Edit: This is still a really rudimentary idea. My plan is for the cities to levitate, rather than actually fly. Making them fly in the first place will be expensive, requiring lots of material components and recasting every six months to ensure that the cities do not crash to the ground and kill lots of people. There will be failsafes and such to make sure that if one casting is missed, it won’t automatically fall, but frequent recasting is needed as “fuel” to keep them there.

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    $\begingroup$ It would be more interesting if you used tech because if you had magic you could just chase the earthquakes off to happen somewhere else. $\endgroup$
    – Willk
    Commented Jan 7, 2022 at 3:11
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    $\begingroup$ Can you edit the question to give more details about how the magic works? Specifically: 1. What types of things can the magic do? 2. How powerful is the magic? What size of effects can the magic produce? 3. What is the mechanism for the magic? Or are you more interested in a justification for why magic can levitate cities but not prevent earthquakes? $\endgroup$ Commented Jan 7, 2022 at 4:25
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    $\begingroup$ It might be interesting if the cause of the earthquakes was the levitating cities. $\endgroup$
    – Dan
    Commented Jan 7, 2022 at 5:36
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    $\begingroup$ Unless the magic is simple enough and cheap enough for ancient folks to discover and use, they will find non-magical solutions. Japan, for example, has many centuries of experience building cities that were fairly earthquake-resistant without magic. $\endgroup$
    – user535733
    Commented Jan 7, 2022 at 6:29
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    $\begingroup$ in a sense, Japanese buildings are already "floating" - not on air, but on an array of springs. The bigger ones come with a big honking chunk of metal at the top just to stop them from swinging around. $\endgroup$ Commented Jan 7, 2022 at 7:12

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I have lived in the area of Japan that experienced the large earthquake in 2011 for ten years now. I think the levitating cities would not be a huge help, and if they cost a lot, would be a very inefficient solution.

  • Most earthquakes are very mild. We have several a year where we feel gentle shaking, look up, everyone remarks that it is an earthquake, we comfort children if necessary, and 10 seconds later it is over and we continue with life. I don't know how many earthquakes I've felt in 10 years. But I know that things have only fallen down 3-4 times. And I was only recently in an earthquake where I couldn't stay standing and where I saw damage walking around the city afterward. Living in a city that could fall and be damaged if expensive and frequent maintenance is not performed sounds much scarier to me than living where I live.

  • The most dangerous part of earthquakes is tsunamis. If your city is close enough to the ocean to risk going underwater and they can levitate the city high enough to be out of reach, that's the only scenario I can think of where this might be worth it. Japan has gone to some pretty drastic lengths to protect the coastline after the 2011 tsunami - it was devastating.

  • The other big danger in earthquakes has been landslides, especially after heavy rain. I wonder if your levitation would pick up large hills / small mountains in and around the city? If the levitated part wasn't higher than all the land, landslides could still be a danger. Landslides are also a big factor for our rivers - so if an earthquake triggers a landslide in the mountains, it could cause the rivers to flood. I don't know how rivers would work in a levitated city, but that is the factor in my city.

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No

consider a few questions, how to they travel outside the city? The only solution I can see is bridges, but if your city gets cut off during every quake as bridges to the ground break it will be far deadlier than just building your city with earthquakes in mind. It will also severely limit travel and thus the economic productivity of your city since you can only have a few bridges. this is similar to the problem ancient cities had with walls they create bottlenecks of traffic and in this case are also prone to breakage.

Ditto for the transportation of water. NYC consumes more than a billion gallons of water EACH day. pipes don't fare any better than bridges, you also now need much more active pumping since your city is high off the ground.

this also means most shipping can't be done by water because docks can't be directly connect to the city.

Also how do they produce food, you need a huge amount of farm land to supply a city. Keep in mind NY City needs an area larger than NY state to feed it. If it grown on the ground then the bridge problem is even worse since food also gets cut off, and now you have the farmers and other people living around the city feeling like second class citizens since they still have to deal with earthquakes.

How to deal with earthquakes

  1. Build far inland, so you don't have to worry about tsunami.

  2. Heavily manage your waterways, you need to worry about flooding but also need to keep shipping open.

  3. Build low squat wooden or steel buildings with dampers, this limits the height and density of your city but also makes it far safer. buildings will also need a lot more horizontal support than ones we are familiar with. Wood or steel buildings can flex and a damper will keep sway to a minimum. Building buildings tapered as they go up will help as well.

  4. Redundancy, every major system needs several layer of redundancy, because you will always have the risk of fault lines cutting things and this ensures even when there is damage it is not disruptive.

  5. Accessibility, this comes in two forms, you need many ways in and out of the city so lifelines cannot be completely cut. Also utilities need to be built with ease of access in mind, you will never no what will need repair.

  6. Don't build bridges or if you do vastly over build them and use steel and wood again. stone is a horrible building material in earthquake prone areas.

If you want a way to include floating magic, don't float the city, float individual buildings just a few inches off the ground, basically recreating modern floating bearing supports with magic. this will let you build larger buildings without being too different than normal cities and still be very earthquake resistant. this also means when failures occur it is single buildings and not entire sectors of the city. Japan has actually tried to build something like this, but with magic it ill actually work because it is always on. https://www.popsci.com/technology/article/2012-03/japanese-levitating-homes-could-survive-earthquakes-unscathed/

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  • $\begingroup$ For getting off, install a few mountain cable ways on the side.. also, If they can levitate an entire city, it won't be a problem to get people out. or put some magic temporary bridge which disappear when you leave it. $\endgroup$
    – Goodies
    Commented Jan 7, 2022 at 17:17
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    $\begingroup$ @Goodies cables need to be short to not be affected by earthquakes, and that only allows foot traffic not the important stuff. read the OP's statement making things fly as an expensive time consuming enterprise there is no reason to believe they can just throw up hundreds of new bridges and pipelines in a few minutes. $\endgroup$
    – John
    Commented Jan 8, 2022 at 15:21
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Yes, it is viable. But,

1. It must be trivial for the system to run perfectly.

If you want to float your cities as a solution to earthquakes at a civilization level, at least you should make the magic simple and cheap. Otherwise, peoples of your civilization will just default back to what works but simpler and cheaper. Actively maintaining a high-tech, sophisticated, resource-intensive support system does not sound like a very good thing to do in the long run, especially for something as foundational as the literal foundation for your city.

  • What if the tech (magic) fails mysteriously?
  • What if the resources (mana/spellcasting costs) suddenly gets expensive?
  • What if rival city-states exploit a weakness in my system (assassinate the mages, steal the runes, counter the magic) to bring it down crashing to the ground, Sokovia-style?

I mean, if the magic suddenly turns off, your city ... falls, literally. Not to the hands of your enemy, but to sea level.

2. Remember, stuffs that exist on the ground does not automatically exist when floating.

  • Water: there's significantly less groundwater when you're not on the ground, and make sure not to go above the clouds because otherwise rainwater starts its fall below you.
  • Atmosphere: if you go too high, air gets too thin and the temperature gets cold.
  • City limits: going off-limits means going down, so make sure to put preventive (and possible curative!) measures.
  • Space: there's significantly less space to expand, going suburban means going down so land will be even more luxurious commodity. Space allocated for food generation (farmland) will also be an issue over time.
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  • $\begingroup$ food will also be an issue, cities need a LOT of farmland to support. $\endgroup$
    – John
    Commented Jan 7, 2022 at 16:33
  • $\begingroup$ @John Good point. It will make the available space for expansion even less, significantly. $\endgroup$
    – Nuclear241
    Commented Jan 8, 2022 at 15:16

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