Eastern U.S. Quake, 5.9

A rather large earthquake occurred in northern Virginia at 1:51 pm local time today, giving Washington DC and neighboring states a good rattling. People 1000 kilometers away felt it. The U.S. Geological Survey's Community Intensity map (the "Did You Feel It?" map) shows abundant reports to the edge of the map, including Ohio, South Carolina and New Jersey. But a friend of mine felt it in northern New Hampshire, and the New York Times reports that it was felt in Ottawa. This is typical of quakes outside the western mountains, because the North American plate is thick and cold and rigid, allowing seismic waves to go farther before fading out. UPDATE: I've found published reports of people feeling the earthquake in Atlanta, eastern Tennessee and Kentucky, Illinois, Toronto, Quebec City and Augusta, Maine.

Virginia's largest quake on record was in 1897 and is estimated to have magnitude 5.9, the same as today's event. Given that no seismometers recorded the 1897 quake, we can say confidently that today's event is largest ever recorded in Virginia. And maybe the data from today's quake can help us better calibrate the 1897 one.

The eastern states are earthquake country, although large events are much rarer than in the west. Notable events occurred in 1638, 1755 and 1886. The 1886 event was a 7.3 event in Charleston, South Carolina. That probably shook the region more strongly than today's quake.

Baseball at the Nationals' stadium in Washington was delayed a few hours, but what caught my eye was what the owner told MLB: "I knew what it was immediately. A lot of people thought it was an explosion—either in the building or across the street in the concrete plant. I felt the swing immediately and knew it was an earthquake." Remember that: Feel the swing. Earthquakes swing because of their low-frequency vibrations, unlike explosions. Little quakes thump or jiggle, middle-size quakes rock or swing. Big ones are like nothing else on Earth.