a 5.9 on the Richter scale. And it was felt pretty strongly here in NYC, which does get earthquakes from time to time. The last "big one" hit October 27, 2001 and was a 2.6. That one was quicker than today's quake, which lasted over 30 seconds.
Back in March, the NY Daily News ran an informative piece about the history of earthquakes here in New York. The city has had it's share of "big one"s, a 5.2 in 1884 and 1737 that originated closer to home. As for something of a magnitude of 7 or more, that is incredibly rare, happening only once ever 3,400 years. But yesterdays event was big news anyway, seemingly amplified by all the social media tremors that were sent out in its wake.