System and method for event-based updating of user profiles UP of users U in a social network and formation of new communities based on a resonance condition. A database of user profiles UP with profile domains D based on self-reports as well as observed network behaviors is deployed. The user profiles UP of users U in groups G attending an event are re-compiled by an event-based updating module based on event responses ER. Further, the event-based updating module identifies a profile change ΔP* in at least one of the profile domains D of user profiles UP, and the new community is formed by the event-based updating module from a subgroup SG whose profile change ΔP* indicates a mutual resonance or consensus in their event responses ER.