Have you ever lived in California, or any other place where earthquakes are common? It sounds as if you have not. They now build tall buildings with things like built in rollers and shock absorbers so they can flex and sway with the shocks, which are not infrequent. A really large earthquake can move the relative positions of objects on opposite sides of the fault by many meters. Also the ground can liquefy and erupt if its wet.
Earthquakes definitely would and do pose a threat to tunnels. They have various ways to adjust to this, I am not saying its "impossible" but it definitely would and does add substantially to costs and the planning thats required.
Otherwise this hype-train could find itself suddenly making a little directional adjustment... underground, at 500 mph!
If you calculate the projected cost to build the high-speed train from SF to LA every man women and child would have to make that trip 100 times, paying $100 just to cover construction costs/
You just made this up. You have no actual data on this.
You are right what happens if there is an earthquake and the ground shifts 25 feet?
Earthquakes usually pose no serious threats to underground systems, especially if you dig deep enough. Most of the damage happens on the earth surface. It's pretty much the same as waves on water, where the water underneath is calm.
This statement of yours could not possibly be true. Earthquakes are definitely an underground phenomenon, not a surface one.
One interesting electronics related phenomenon which I have seen, which are still not well understood is, very large earthquakes cause very bright flashes in the sky. (the ones I saw were greenish blue) very much like lightning. This must mean that there are very high voltage potentials in the ground.
I saw this once years ago and for decades I had no idea what it was that I had seen because it was not described in the literature.
But recentlly, thanks to sites like Youtube now there are a great many videos people have taken of them.
So that represents another potential problem that must be planned for. If a high voltage spike is large enough to cause these discharges into the sky, they must be absolutely huge.