No need to wonder, sewer lines that cross a fault line simply break. During my time here in the SF Bay Area I know of at least three water line incidents which were directly caused by water mains that were damaged by earth movement. One in San Francisco in the late 90's created a huge sink hole as the water washed out the under part of a street, one in Berkeley where the REI store flooded, and one in Fremont which may have been a combination of fault motion and land settling.

Yes but they know the fault is exactly there and moving at a constant rate, it's possible they could plan for it.