A souvenir T-shirt for the new Enders Fault Mountain Bike Trail includes a squiggly line that replicates the seismographic reading from a magnitude-4.7 earthquake, part of the Guy-Greenbrier earthquake swarm that struck Faulkner County in 2011.
Enders Fault, which runs through Woolly Hollow State Park, played a role in that quake, says Scott Ausbrooks. Ausbrooks, who grew up in Greenbrier, is an expert on geohazards for the Arkansas Geological Survey in Little Rock.
The temblor immortalized on those shirts (as it were) occurred at the intersection between Enders Fault and another big crack, the Guy-Greenbrier Fault.
When park superintendent Steve Wilson called to ask about geologic features that might be used to name the new trail, Ausbrooks said, there weren't many other options. The rock under the park is part of the Atoka formation, which sounds native, but that package of shale and sandstones stretches all the way to Oklahoma.
Geologic structures typically are named for the places where they begin or are first observed, he said. For instance, Atoka is in Oklahoma. Meanwhile, the Enders Fault is named for the community of Enders, which is 6.1 miles north of the community of Barney on Arkansas 107 and about 7 miles northeast of the park.
Faulkner County has several large and many small faults, he said, and Enders Fault is "a very large one."
"In some places this thing has had over 2,000 feet of displacement. It has moved over 2,000 feet vertically over time. ... It used to be at the same level. The movement is up and down. It's like a step, if you can imagine having a 2,000-foot step.
"If you're on one side of the fault, you're 2,000 feet higher on the north side than on the south side."
So when he thinks about the new trail's motto, "Ride the fault," Ausbrooks said, "I smile."
The Arkansas Seismic Network Survey has just created a poster with photos of the seismic monitoring station at Woolly Hollow State Park. It can be downloaded as a PDF from geology.ar.gov. Under "Geohazards," click "Earthquakes," and look on the left side of the page for "Geohazard maps." Scroll down about halfway and click on "Woolly Hollow State Park."
ActiveStyle on 06/16/2014