This HowTo describes how to install OpenQuake on Mac OS X 10.9 from source.
Note that even though the instructions below seem to work, the result has not been thoroughly tested. OS X is not officially supported by GEM. Unless you have a very good reason to run OpenQuake on OS X it is recommended that you stick to the official platform which is Ubuntu 12.04.
Also, it's fairly involved. You've been warned ;-)