A method includes receiving first media data from a plurality of persons; identifying first media data generated within a window of time at a certain location and associating the identified first media data with an occurrence of a first event; determining which persons of the plurality of persons were present at the occurrence of the first event; and storing information related to the first event in association with information identifying those persons determined to be present at the occurrence of the first event. The method further includes, in response to receiving further media data from a plurality of persons, determining if the further media data was generated within a window of time at a certain location; determining based at least in part of the stored information if the certain location associated with the further media data is the same as the certain location associated with the first media data, and if at least some of the persons from which the further media data is received are the same as the persons from which the first media data was received and, if so, declaring that a second event is occurring that is related to the first event; and sending a notification of the occurrence of the second event to those persons who were determined to be present at the occurrence of the first event and who are determined to not currently be present at the occurrence of the second event.