Update: Natural Resources Canada confirms that there was a 4.3 magnitude earthquake centered near Hawkesbury, Ontario (about 90km or so east of Ottawa) today at 1:36pm: "
"The earthquake of March 16, 2011 occurred in the western Quebec seismic zone. The depth of this earthquake is 12.8 km. On average, we record 100-150 mostly small earthquakes in the region every year. Magnitude 4 events occur on average once every 2-3 years in this region. This event (mN 4.3) is roughly 1/10 the size of the June 23, 2010 Val-des-Bois earthquake (Mw5.0) and 75 km to the southeast. This earthquake was widely felt between Ottawa and Montreal. No significant damage has been reported and none would be expected for an event of this size."
So a pretty minor earthquake really, nothing to see here, please move along. Scott McClare put the earthquake into context: it was less than 1/10000 as intense as the one that hit Japan last week.
A far more significant event in Ottawa today was the fire at the Home Hardware building on Beechwood Avenue. Firefighters are warning residents in the area to stay indoors due to potentially toxic smoke. More info...
Originally posted here at 1:58pm: "Natural Resources Canada reports: "Earthquake S of Hawkesbury, Ont. -- details soon Preliminary automatic detection of a seismic event of magnitude 4.7 at 13:36 EDT on 16 Mar in the region of LACHUTE, QUE." (Source: http://earthquakescanada.nrcan.gc.ca/index-eng.php)
Lots of people felt it here in Ottawa, check out this Twitter feed: Ottawa Earthquake.