How to catch fatal errors

Hello every body, I'm currently working on a very high traffic web sites. I often get a fatal error in production about memory "Allowed memory size of ... exhausted". Unfortunately, I can not reproduce this fatal error in developpement environment. The main reason for that is that I don't know the php script which causes the error. Php only tell me on which file, the error has appeared, but I don't know the orginal php script which were called. I've tried some hacks, like the register_shutdown_function one. This hack allows me to catch almost all fatal errors, except one which says "Allowed memory site of ..." Any idea about how to catch this error? My main issue is to know script that has been called. Best regards