8. A computer program product for detecting an event the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to perform a method comprising: selecting a region and time frame of interest; obtaining a set of social media data streams associated with the region and the time frame of interest; applying a lexical graph generation algorithm to the set of social media data streams to obtain lexical graphs; performing similarity analysis on the lexical graphs based on candidate lexical graphs related to the event to generate matching data; and investigating the event based on the matching data.
18. The computer program product according to claim 8 , wherein each lexical graph of the lexical graphs, and each candidate lexical graph of the candidate lexical graphs, is constructed based on repeating patterns of words.