Would the water system even survive it? That’s some dry country, without a water system.
That’s a good question. Much of the water supply pipes in the LA area are old and rotted. I’d guess a 7.8 would cause countless water main ruptures. And this isn’t good, because at that magnitude, there would be fires everywhere...
In a truly big quake, the water system will not survive. Attended another briefing (a few years later in San Bernardino) where the focus was on a major quake on the southern section of the San Andreas fault.
Bottom line: the Pacific Plate will lift and move North, several feet at a minimum and probably as much as ten feet or more. Every aqueduct, freeway, gas line, railroad, and perhaps the electrical transmission lines will be severed. The LA basin will be cut-off from the east.