"Inspired by XKCD, [here's a] heat map of the frequency of tweets mentioning the word "earthquake" in the 5 minutes after the Virginia earthquake on 08/23/2011. The locations are self-reported by Twitter users and may be erroneous. The spread of the earthquake is approximated to be 4000 m/s."And see here actual seismometrics across the US...
25 August 2011
TweetQuake ~ Twitter Outraced VA Quake Vibes!
Twitter outpaced geological vibrations during recent VA 'quake!