Tunnels adjacent to faults.
In California.
Yeah, that’ll work.
Tunnels, when designed properly, are known to be one of the safest places to be during an earthquake. From a structural safety standpoint, the tunnel moves uniformly with the ground, in contrast to surface structures. Additionally, a large amount of earthquake damage is caused by falling debris, which does not apply inside tunnels. Some examples:
1994 Northridge Earthquake: no damage to LA Subway tunnels
1989 Loma Prieta (Northern California) Earthquake: no damage to tunnels, which were then used to transport rescue personnel
1985 Mexico City Earthquake: no damage to tunnels, which were then used to transport rescue personnel