1. A system to detect an event, the system comprising: a memory device configured to store candidate lexical graphs; and a processor configured to: obtain a set of social media data streams associated with a region and a time frame of interest; apply a lexical graph generation algorithm to the set of social media data streams to obtain lexical graphs; perform similarity analysis on the lexical graphs based on the candidate lexical graphs related to the event to generate matching data; and provide information for investigation of the event based on the matching data.