My Physical Geography 100 class says pretty much that you want the right kind of bedrock. Obsidian, for example, that's great stuff to have under your feet because it barely moves at all. But the guy next to you on sandstone, he's screwed, because obsidian transmits the waves well even if it doesn't actually move much. (This is why in the event of The Big One hitting San Diego, most of La Jolla will still be standing.) Mexico City was an unpredictable occurance but soil liquefaction is not, so all that swampy land might just come back and bite you unless you're on the right kind of bedrock.
Basically, studies have shown that anything aside from rock is probably asking for trouble. The San Francisco earthquakes prove the point: those parts of the city built on swampy land were flattened along with the fill portions. The Presido, which is built on an area with obsidian bedrock, didn't feel a thing.
