Arkansas Earthquake Swarm Jolts Residents

Geologists actively seeking cause of earthquakes

related: New Fault Raises Threat of Eastern Earthquakes – flashback





October 11, 2010
By Megan Reynolds
Log Cabin Democrat

Geologists with the Arkansas Geological Survey are looking into the cause of a series of earthquake events happening daily in Faulkner County, including a 4.0 magnitude earthquake recorded two miles southeast of Guy early Monday morning.

Gamma Ray BurstAccording to the USGS website, aftershocks ranging in scale from 1.6 to 3.5 magnitude were recorded throughout the morning.

Scott Ausbrooks, geohazards supervisor with the Arkansas Geological Survey, said the quakes are likely a product of Mother Nature, though geologists have not ruled out the possiblity that the quakes are being caused by oil and gas deep injection disposal sites.

Ausbrooks said the area is considered “seismically active,” likening the land to the Enola Swarm area of the 1980’s.

“What we are seeing are clusters of earthquakes in Greenbrier, Damascus, Enola — the areas there are all geographically similar,” Ausbrooks said.

According to Ausbrooks, the AGS has been monitoring the area “off and on” all year, comparing data to determine a cause.

“If you look at the earthquakes on a map, and if you compare them to the location of some 3000 gas wells in that area, you just don’t see a temporal,” Ausbrooks said. “Right now we don’t see any evidence that the vertical or horizontal drilling wells have anything to do with it.” Salt water disposal wells, he said, have not been ruled out.

“We’re hoping to look at their level of injection and see if there is correlation,” Ausbrooks said. “If this is associated with some of the disposal well activity, separating what is natural and what is trigger is problematic. At this time we just don’t know.”

Ausbrooks attributed the recording of recent activity to the Arkansas Seismic Network, which has only been implemented over the course of the past year.

“The goal was to lower the detection threshold,” Ausbrooks said. “So prior to last year, smaller earthquakes could have occurred and we would not have known it — now we’re picking up a lot more. Part of it is our ability to be detecting, but I do believe that we are above average on our earthquakes.”

The earthquakes, he said, are likely to continue, but what Ausbrooks said he does not expect is an earthquake of catastrophic proportions.

“Don’t expect large, damaging earthquakes. The sky is not falling,” Ausbrooks said. “Historically, in swarms like this, you may get a 4.5, maybe a 5.0 magnitude — no major structural damage, but possibly some broken china.”

And as for the reason Monday morning’s quake was reportedly felt exponentially stronger than typical by area residents, Ausbrooks explained, “For every magnitude you go up on the scale, you’re experiencing 32 times more energy released, and that can make a big difference.”

Faulkner County Judge Preston Scroggin said on Monday his office was working hand-in-hand with the USGS and AGS to determine the cause of the activity.

Faulkner County OEM Director Sheila Maxwell reported “lots and lots of phone calls” Monday from concerned members of the community.

“Today I’m working to try to gather information as to who felt it,” Maxwell said. “I’m trying to coordinate a public forum with the USGS, and we’re probably going to have that in Guy the week after next.”

Maxwell said preparedness literature is available to the public at the county OEM office.

Stephanie Newland, principal at Greenbrier Westside Elementary, said some students thought the earthquake was “cool.”

“They handled it pretty good,” Newland said. “I think it happened so fast there was just not enough time to panic or scream. I think it just startled them. We survived.”

Newland said the teachers were reminded of the school’s policy on earthquake procedures and were advised to go over them with the children.

“We wanted to kind of remind them of what to do — we weren’t trying to scare them, just to prepare them and sort of calm their nerves.”

Newland said it was “a good reminder” for the district to “keep on their toes” in terms of emergency preparedness.

Area residents who feel any earthquake activity are encouraged to go online and visit the USGS “Did You Feel It?” site at http://earthquake.usgs.gov/earthquakes/dyfi/

Over 260 responses were recorded by noon on Monday, with claims reaching as far north as Fayetteville and West Plains, Mo. and as far south as Little Rock.

http://thecabin.net/news/local/2010-10-11/geologists-actively-seeking-cause-earthquakes