Why were cities built on the San Andreas Fault?
The famous earthquake zone known as the San Andreas Fault lies underneath the extreme west coast of the U.S., which includes San Francisco, San Jose, and Los Angeles, as well as dozens of other population centers. History tells us that these cities were erected there for all the reasons that populations choose sites: transportation (here, the Pacific Ocean, especially San Francisco Bay), natural resources (for example, the Gold Rush), etc. In the centuries when these population centers were establishing themselves, little was known about the locations of tectonic plate movements, etc., and certainly economic concerns trumped fears of possible natural catastrophes (the same can be said of any coastline; consider New England and its notorious storms). While contemporary expansions (driven by technological advances in the San Jose area, for example) take earthquake possibilities into account, those possibilities do not drive populations away.