Reservoir water weight blamed for Arkansas earthquake swarm

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A swarm of earthquakes in northern Arkansas is being linked to the weight of the water at a rain-swollen reservoir.

The water level at Bulls Shoals has risen 42 feet because of rainfall since March 1, and the weight of the additional water likely triggered 10 earthquakes over five days last week near Harrison, said Arkansas Geological Survey earthquake geologist David Johnston.

The quakes were small, ranging from 1.5 to 3.6 in magnitude, but aren't expected to end soon, Johnston told the Springfield News-Leader . He said the quakes weren't related to hydraulic fracturing, an oil and gas drilling process, or injection wells.

"It's the same process when you let the water out of the lake," Johnston said. "When you lower the lake, you can then relax that pressure and cause small earthquakes again."

Johnston said there weren't immediate reports of damage following a 3.6 magnitude quake on June 11, when the swarm started. But he said some people reported houses creaking and pictures rattling on walls. The quakes were near Harrison, a city about 140 miles north of Little Rock.

Local resident Will Presley said the quake opened a sinkhole in his yard.

"It shook the whole house, and the first thing I thought was that it was the sinkhole," Presley said. "It was just so loud. The shaking went on for 15 or 20 seconds or so. I just knew my house was off in that sinkhole."

Presley said the sinkhole has been filled, but that Harrison officials are planning to work on stabilizing it more.

The depth of the earthquakes ranged from just over a half-mile underground to about 3.7 miles underground. The Arkansas Geological Survey plans to add more ground-detection devices to better record where the earthquakes are occurring.