Friday quake called 'normal' New Madrid event

LITTLE ROCK -- A small 2.5-magnitude earthquake centered near Manila on Friday morning was the first Arkansas quake recorded this month and an indication seismic activity in the state is returning to normal, geologists said.

The quake occurred at 5:45 a.m. Friday about 7 miles southeast of Manila in western Mississippi County.

A Mississippi County Sheriff's Office dispatcher said she received no calls about the earthquake.

Generally, temblors below 3.0 in magnitude often go unfelt, U.S. Geological Survey officials have said.

Friday's quake is the first recorded in the state since Aug. 29, when a 2.4-magnitude tremor rumbled about 4 miles north of Viola in Fulton County. It was also the first measured on the New Madrid Seismic Zone in Arkansas since a 1.5-magnitude quake shook near Etowah in Mississippi County on Aug. 21.

The seismic zone is an active earthquake fault system that runs from southern Indiana and Illinois, through the Missouri bootheel and into northeast Arkansas. Another series of faults runs along the Missouri and Arkansas border and into northern Mississippi.

In 1811-12, three earthquakes occurred in Arkansas and southern Missouri that were believed to be the largest ever to hit the continental U.S. Scientists estimated the quakes could have reached 8.0 in magnitude.

Arkansas Geological Survey geohazards supervisor Scott Ausbrooks said the decrease along the New Madrid Seismic Zone is "normal" at times.

"Things are getting back down to normal background seismicity," Ausbrooks said. "There have been a few New Madrid events in Missouri, and that's normal. But we're seeing a return to an average earthquake cycle."

He said earthquakes in central Arkansas -- primarily around Faulkner, Conway and Van Buren counties -- have also decreased after natural gas operations in the area discontinued using injection wells to dispose of waste water. Natural gas injection wells caused hundreds of earthquakes there three years ago, geologists said.

"There is a correlation," Ausbrooks said. "The injections went down, and the [seismic] activity began falling."

He said the lack of earthquakes along the New Madrid zone does not necessarily mean pressure is building and a large quake is imminent.

"It's just episodic," Ausbrooks said. "It's all part of the normal process."

NW News on 09/13/2015

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