ausearch with message types does not return what I think it would return. (0 matches when adding a user)

Good day, I am new with auditd, and got some issues.. For example, When I add or delete a user, I cannot see the entry with ausearch -m ADD_USER, it returns 0 match, BUT its logging it under USER_AUTH. If I do a ausearch -x adduser, ill thee se event audit.log with the EXECVE Type: # ausearch -x useradd | grep titi type=EXECVE msg=audit(1435677075.900:49410): argc=2 a0="useradd" a1="titi" I also tried to find a full description of all message types returned by ausearch -m but could not find any.. Any help on this would be appreciated as well. Many thanks.