Aside from the cost, I can’t see how they could compensate for earth movements. The last thing I’d want is to slam into a side at 800 mph because the tunnel moved over by three inches.
They are trying to address that, although I don't know how feasible it really is for complete safety. If there were a real earthquake, the tube would have to be shutdown immediately. And if you are travelling at 700 miles an hour and it moves, you'd become a statistic. But if they are safe on every other occasion, they would still be better than cars.