Twenty-six small earthquakes have rattled the state of Oklahoma over the past week — including seven on Saturday alone — according to data from the U.S. Geological Survey (USGS).

Most of the temblors have ranged from 2.5- to 3.9-magnitude over the past seven days, but USGS recorded an earthquake of 4.3-magnitude at 5:11 p.m. CDT on Saturday. The epicenter was about 4.9 miles south-southwest of Langston, OK.

During the week, the USGS recorded seven earthquakes that measured between 3.0- and 3.9-magnitude. The first, a 3.3-magnitude temblor, hit Friday afternoon about 10.5 miles north-northeast of Enid, OK, while a second quake measuring 3.2 struck Saturday morning about 5.6 miles south-southwest of Langston. A third, of 3.0-magnitude, also hit Saturday, about 4.9 miles east-southeast of Guthrie, OK.

USGS recorded two earthquakes between 3.0- and 3.9-magnitude on Monday, and another three on Tuesday. Monday’s quakes measured 3.3 and 3.9 and hit 5.6 miles south-southwest Langston and 10.5 miles southwest of Medford, OK. On Tuesday, quakes measuring 3.0, 3.9 and 3.8 hit 4.9 miles south of Medford, 4.9 miles north-northeast of Harrah and 3.1 miles north-northeast of Harrah.

“The earthquake activity hasn’t stopped in Oklahoma,” Justin Rubinstein, geophysicist with the USGS, told NGI’s Shale Daily on Tuesday. “There’s been a number of studies looking at earthquakes in Oklahoma that have pointed to wastewater injection wells being responsible for those earthquakes.

“We can’t say that for all of the earthquakes in Oklahoma because they haven’t been carefully studied. But certainly a number of these earthquakes appear to be induced by wastewater injection.”

Last week, researchers at three universities and the USGS said four wastewater injection wells with high disposal rates could be responsible for up to 20% of the earthquakes that hit Oklahoma between 2008 and 2013 (see Shale Daily, July 7). Researchers have also attributed a 5.7-magnitude earthquake near Prague, OK, in 2011 to wastewater injection (see Shale Daily, Oct. 25, 2013).

Two months ago, the USGS and the Oklahoma Geological Survey issued a joint report that said 145 earthquakes of 3.0-magnitude or greater had occurred in the state so far in 2014 (see Shale Daily, May 6).