Seventeen minor earthquakes have shaken the ground in extreme northern Arkansas in the past seven days and officials with the United States Geological Series are attributing at least some of them to the swollen waters of the Bull Shoals Lake, which straddles the Arkansas/Missouri border.
The area north of Harrison and in the Bull Shoals Lake region has been hit with ten shakes since last Sunday ranging from 1.5 to 3.6 multitude on the Richter scale. Harrison is about 25 miles southwest “as the crow flies” of what is considered the center of the massive lake system.
David Johnston, earthquake geologist with the Arkansas Geological Survey, said on Friday in a press release that the tremendous weight generated on the seismic plate formation in the area from a high volume of water being retained at Bull Shoals is a mitigating factor.
Johnson said the lake level, which has risen by 42 feet since March is applying more than six trillion pounds of pressure to the bottom of the man -made reservoir in the Ozarks.
Bull Shoals Lake impounds the White River for the last time as water travels toward its mouth on the Mississippi River. Bull Shoals is the lake farthest downstream in a chain of four artificial lakes that include (from upstream to downstream) Beaver Lake, Table Rock Lake and Lake Taneycomo in Missouri.
The lake is controlled by the Army Corps of Engineers and has the primary purpose of flood control. The level of the lake fluctuates regularly with a normal pool level elevation of 654 feet above sea level.
However, the lake regularly fluctuates between an elevation of 630 to 680 feet and was close to 390 feet throughout the past week.
Eventually, says Johnson, something has to give.
The earth has regulated itself with the series of earthquakes which included three last Sunday, one each on Tuesday and Wednesday, four on Thursday and one on Saturday just after 4:30 p.m.
Johnston reported a team from Arkansas Geological Survey will be placing more seismometers (ground-motion detection devices) in the quake zone to better record what is happening and to get a better feel for the depths underground where the quakes are happening.
The deepest so far has been about 3.7 miles, while the shallowest is estimated at just over a half mile underground.
Johnston said there are no reports of damage from the 3.6 magnitude quake early Sunday morning. But some people reported houses creaking, china shaking on shelves, pictures rattling on walls and glasses of water sloshing on tables.
There were reports of experiencing effects of the Sunday earthquake from citizens compiled by the USGS from seventeen counites in Arkansas and Missouri as well as Delaware County in northeast Oklahoma.
