They won't break, but they may screw-up in-progress wafers and need to be realigned. You're right that they're incredibly sensitive, and they've built this into the design of the fab. They float the masks, objectives, and wafers on pneumatic isolators (separate stages for each, I believe). Extra-sensitive machines will also be individually isolated from the rest of the fab to prevent adjacent machines and footsteps from interfering.

Here's an example of a common pneumatic isolator, the kind of which can be found in almost every lab making optics:

https://www.newport.com/f/pneumatic-vibration-isolators-with...

A lot of this is from memory so...possibly wrong...

Very but also its solveable. You stop manufacturing, realign the tools, and then move on. With the 2011(?) japanese earthquake, there were impacts of the earthquake vibrations on lithography well beyond Japan - and it took a while for the earth to settle back down to the point that lithography was stable again. Aftershocks, tsunamis, reverberation of earthquake energy are all sources of vibration that can affect lithography.

The bigger issue (to me with what you are saying) is actually within the semiconductor supply chain. At least when I was involved, many/most/a huge fraction of the basic wafers come from Japan. Two of the major players were (are?) SUMCO and Shin-etsu, and they had huge fleets of CZ furnaces because power was relatively cheap, and more importantly, generally very stable. The process time for ingot (the precursor to wafer) growth is on the order of like weeks/months and is very energy intensive. So, power stability is a big deal. The power issues after the earth quake had huge impacts on wafer availability over the following year or so.

Like Japan, Taiwan is also on the Ring of Fire, and is no stranger to earthquakes.

We know how to make earthquake resistant buildings and foundations for decades now.