earthquake

The United States Geological Survey (USGS) reported that a small quake, originating in Putnam County, registered a 2.1 on the Richter scale at around 7:20 a.m. Wednesday.

No damage was reported.

An earthquake of similar magnitude, 2.3 on the Richter scale, occurred in the same area last April. 

The Richter scale is used to measure magnitude of earthquakes.

Earthquakes in this area aren’t all that uncommon, although they typically register a low magnitude.

“The Oconee River valley occupies an area that has probably been a drainage area for a long, long time — we’re talking like 10s or 100s of millions of years since the Appalachian Mountain chain started forming almost 300 million years ago,” Georgia College geology professor Dr. Doug Oetter said after April’s quake in Putnam County. “Oftentimes, rivers occupy places that had, for whatever reason, some sort of a geologic fault (crack in the bedrock) underneath it. That crack has probably been there for over 100 million years. Every so often, about 3 miles down, as the seismograph told us, the fault can slip because these are old structures that are moving around just a little bit. What I've heard is that a lot of times these are caused by the water in the reservoir.”

The reservoir, Lake Sinclair, can help create earthquake-favorable conditions on occasion.

“After a significant rain, especially if Georgia Power is holding onto their water, the level can come up and the rainwater can help lubricate things down underneath,” Oetter added. “The weight of the reservoir is one of the things that can help move those sediments around along that old fault. They have a name for it called, ‘reservoir-induced earthquakes.’ The ones we’ve seen tend to be focused in and around the lake. They usually tend to come when there’s a high water level at the lake, and a lot of them came on the heels of a significant precipitation event … People tend to forget how much water weighs.”

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