My there was a lot of ground shaking going on yesterday!  This morning the NYT published a telling map showing how far away people reported the shaking…an impressive distance.

vaquake shake
Comparing two similar quakes in two different parts of the United States...significant difference in how far away the ground shaking is felt. (Source New York Times)

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).

Yesterday’s earthquake occurred on a north or northeast-striking plane within a previously recognized seismic zone, called the “Central Virginia Seismic Zone” (CVSZ).  The CVSZ has produced small and moderate earthquakes since at least the 18th century. The previous largest historical shock from the CVSZ occurred in 1875 and occurred before the invention of effective seismographs, but the felt area of the shock suggests that it had a magnitude of about 4.8. The 1875 earthquake shook bricks from chimneys, broke plaster and windows, and overturned furniture at several locations. A magnitude 4.5 earthquake, December 9, 2003 also produced minor damage.

Right after I heard about the quake I started Googling for information…what blew me away was the Wikipedia had already placed a “placeholder for information” on their page on the Virginia Seismic Zone…that was within 20 minutes of the ground shaking!!!!  Wow…social media and the internet…blazing!

For those of you in the East and Midwest this is a bit of a wake up call.  Earthquakes happen throughout the United States, albeit more commonly in the West.  Take a look at your emergency response and business continuity plans this morning through fresh, earthquake filled eyes.

Oh, and by the way, the largest natural earthquake in Colorado in more than a century struck Monday night in the state’s southeast corner, but there were no reports of damage or injuries. The quake, with a preliminary magnitude of 5.3, was centered about nine miles from the city of Trinidad and hit at 11:46 p.m. local time. It was felt as far away as Greeley, about 350 miles north, and into Kansas and New Mexico.

http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/se082311a.php#summary

http://www.nytimes.com/2011/08/25/us/25quake.html?_r=1&hp