We study the dynamics of public media attention by monitoring the content of online blogs. Social and media events can be traced by the propagation of  word frequencies of related keywords. Media events are classified as exogenous-where blogging activity is triggered by an external news item-or  endogenous where word frequencies build up within a blogging community without external influences. We show that word occurrences exhibit  statistical similarities to earthquakes. Moreover the size distribution of events scales with a similar exponent as found in the Gutenberg-Richter law. The  dynamics of media events before and after the main event can be satisfactorily modeled as a type of process which has been used to understand  fore-and aftershock rate distributions in earthquakes-the Omori law. We present empirical evidence that for media events of endogenous origin the  overall public reception of the event is correlated with the behavior of word frequencies at the beginning of the event, and is to a certain degree  predictable. These results imply that the process of opinion formation in a human society might be related to effects known from excitable media.