What caused the earthquakes that shook N.C.’s mountains this week?

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RALEIGH — Four small earthquakes that rattled the mountains in western North Carolina earlier this week aren’t anything to get all shook up about.

Quakes that minor, which ranged from 1.7 to 2.7 magnitude, are common in that part of the state but rarely felt. Quakes in sparsely populated areas typically go unnoticed.

The U.S. Geological Survey compiles reports from people who feel earthquakes and submit the information online. North Carolina’s state geologist, Kenneth Taylor, said 174 people reported feeling the largest of the four quakes, on June 10; there were no reports on the other three dates.

Most earthquakes occur unnoticed and are a normal process that allows the earth to ease built-up geological strain.

“These are essentially normal, small earthquakes associated with very old faults that formed during the building of the Appalachian mountains,” Sarah Carmichael, an associate geology professor at Appalachian State University, said in an email Thursday. “The faults themselves aren’t active anymore in terms of tectonics, but as the North American plate moves/shifts with time and builds up stress, these little faults will be the things that can move a bit to diffuse some of the stress on the plate.”

She said some of the motion is likely due to aftershocks related to extremely old earthquakes.

This week’s quakes began with a 2.7 magnitude about 8 p.m. Sunday between Burnsville and Spruce Pine, followed by a 2.0 at 8:16 a.m. southwest of Hays. The third was a 1.8 at 10:40 p.m. Tuesday southwest of Newton, and a 1.7 at 1:12 a.m. Wednesday east of Mountain View.

Advances in technology have allowed for a much more detailed mapping of small earthquakes, Taylor said. A map from earlier in the week shows a smattering of seismograms from stations in North Carolina operated by the U.S. Geological Survey and the Center for Earthquake Research and Information at Memphis State University.

News of this week’s earthquakes sparked discussion online about their significance and what caused them.

Taylor and Carmichael said they had nothing to do with fracking or the companion process of injecting waste fluid into the ground. Nor have there been test wells drilled in that area.

Conventional oil and gas drilling in Virginia and Tennessee are too far away to have caused this week’s temblors, Taylor said.

Fracking is not permitted anywhere in North Carolina at this time.

Though they are not as common nor as destructive as earthquakes in the west, there have been significant events that either had their epicenter in North Carolina or caused damage from outside the state.

Other quakes that had an impact in North Carolina include:

  • A 5.8 quake in Virginia knocked a spire off of the National Cathedral in Washington, D.C., in 2011, and was felt from Georgia to Massachusetts. It panicked hundreds of tourists in Washington.
  • A 4.5 magnitude quake near Richmond, Virginia, in 2003 that was felt in Raleigh.
  • 3.5 quake in Henderson County in 1981.
  • 4.1 quake in McDowell County in 1957.
  • 4.0 quake in Jackson County in 1957.
  • 3.7 quake in Buncombe County in 1957.
  • 5.2 quake in Mitchell County in 1926.
  • There was a 5.5 quake in 1916 near Asheville.
  • A 7.3 magnitude quake in 1886 centered in Charleston, South Caronlina, and caused damage here. It was felt from the East Coast to the Midwest.
  • 5.1 quake in Wilkesboro in 1861.

Source

http://www.greensboro.com/ap/north_carolina/what-caused-the-earthquakes-that-shook-n-c-s-mountains/article_eb4d5d79-6210-540c-9e91-7be93358160b.html

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