LITTLE ROCK — Scientists are installing more seismic monitors this week in an area north of Conway that has been the center of hundreds of earthquakes that began rumbling last fall.
The U.S. Geological Survey will place two additional sensors near Guy and Greenbrier to record the earth’s movements, said Scott Ausbrooks, geohazard supervisor for the Arkansas Geological Survey.
The monitors are used together to pinpoint seismic activity, he said.
Geologists have measured more than 750 earthquakes since September along a fault system between Guyand Greenbrier in northern Faulkner County. Scientists have not determined if they are caused naturally, or if fluid injections by gas and oil drilling crews play a role.
The quakes have generally increased in frequency - and lately in intensity, too - during the middle of each month.
Twenty-two were recorded Thursday, and 15 shook the area Friday, including one that registered 4.1 in magnitude, which was the most intense quake measured since the swarm began nearly six months ago.
Scientists also recorded 15 more Sunday and at least eight Monday.
The new monitors willhelp scientists study the series of earthquakes that have startled residents since they began rocking the area last September.
The temblors began on the northern edge of a fivemile long fault near Guy. Ausbrooks said the latest batch of quakes are rattling along the opposite end of the fault.
“They’re on a previously unknown fault that’s been highlighted by the seismicity,” he said.
There are six major faults between Clinton and Conway. Most run east and west, but the fault that’s responsible for the series of earthquakes juts off and runs northeast and southwest, he said.
The Center for Earthquakeand Research Information in Memphis will analyze the data recorded by the monitors, said center director Gary Patterson.
He said scientists there have ruled out the hydraulic fracturing methods companies are using to drill in the Fayetteville Shale because the drilling goes only about 1.5 miles deep. The quakes are centered along faults between four and six miles deep, he said.
However, the disposal injections of saltwater used in drilling have not been discounted yet, Patterson said.
“We don’t know what’s causing them,” Patterson said. “We need to continue looking at the data.”
Northwest Arkansas, Pages 7 on 02/22/2011