A “rupture” in the ground has been discovered in the North Carolina community that saw widespread damage during a 5.1 magnitude earthquake in 2020, according to a peer-reviewed scientific paper published this month in the Geological Society of America.
Initial mapping shows the “surface rupture” is at least 1.5 miles long, and appears southeast of Sparta as a step-like scarp that reaches heights of around 9 inches at its tallest, the scientists reported.
It exposes a previously unknown fault in the earth, representing “the first documented surface rupture earthquake in the eastern U.S.,” N.C State University says.
Geologists have named the newly discovered fault line the Little River fault, and they note there is evidence earthquakes happened there in the past.
Participants in the research included representatives of the U.S. Geological Survey and lead author Paula M. Figueiredo..
The earthquake occurred at 8:07 a.m. Aug. 9, 2020, and was shallow — centered just three quarters of a mile below the surface. Still, it damaged “roads, utility lines, and masonry structures,” and shifted the foundations of some structures, the paper notes.
“It’s very rare that a moderate magnitude earthquake (the Sparta quake was a 5.1) will create a rupture at the surface,” according to the N.C. State University release.
“Most earthquakes are generated along fault planes located deep within the Earth (commonly five to seven miles below the surface), and a moderate earthquake that deep does not have enough energy to break the fault all the way to the surface,” the university reports.
The earthquake happened along a “reverse fault,” a type of ground motion that pushed one side up and placed it on top of the other side.
“In this case the south of Sparta was pushed up,” Figueiredo told McClatchy News.
It runs through wooded areas, empty fields and commercially developed sites, including Sparta’s Greenway Drive industrial park where several buildings atop the rupture saw moderate damage. Several residential houses up the hill from the rupture ground were severely impacted. The rupture also caused buckling of Rivers Edge Road, breaking “a buried water pipe,” the paper says.
The crack also runs through areas of dense forest growth, which prevented the scientists from making a closer inspection immediately after the earthquake in those spots, the paper states. Survey methods that can look though vegetation have been used more recently, allowing the scientists to extend the length of ground breaking, Figueiredo says.
Study is ongoing at the site of the rupture, she said.
“There is so much here left to understand – we don’t even know when the fault line formed – but hopefully this earthquake can tell us more about these shallow quakes not only in North Carolina, but all over the world,” Figueiredo said in an N.C. State release.
“These less active faults ... tend to move when there are pressure changes on the surface above them. These pressure changes can be due to things like sediment or water being added or released over time,” Figueiredo continued. “... But these characteristics don’t apply in the Sparta region, which means that there may be something else at play that we don’t fully understand yet.”