This search has some good links: https://www.google.com/search?q=effect+of+earthquakes+on+tunnels https://www.google.com/search?q=effect+of+earthquakes+on+tun..

This search has some good links: https://www.google.com/search?q=effect+of+earthquakes+on+tunnels https://www.google.com/search?q=effect+of+earthquakes+on+tun... I don't have a structural engineering background so I'm having a tough time imagining how someone could make a train-track or hardened tunnel "flexible" but I'm sure there are many ways. It doesn't seem too hard to predict the movement of the plates and build in automatic adjustments for the track/tunnel. Have a way to automatically extend track/tunnel and move it laterally to adjust for any minor plate movement. It seems like it would be cheaper and just as effective to build higher speed rail beside of existing rail lines. Or maybe some sort of independently powered train cars that are private so that there are no unnecessary stops, more automated, and can travel faster. Train tracks likely already have to compensate for the faults somehow, though their probably slightly simpler. Regenerative breaking would be nifty technology to build into the trains/cars/vehicles and musk has teams with significant experience in these fields. I imagine that, with all the of top-tier engineers that Musk has on his payroll at tesla, spacex, and solarcity, he can get plenty of suggestions for how to overcome or prevent several feet of movement in the track, humans have done more complicated stuff than that. Then make sure to make redundancy and backup of backups to prevent loss of life and help prevent gridlock in the event of a major disaster (vehicles could go backwards maybe?).