Chadron area earthquake centered on recently-discovered fault

Jennifer Balmat, adjunct professor of geoscience at Chadron State College, has been studying surface expression of features, known as lineaments, as part of her master’s thesis. A lineament is a line that is visible on satellite images and aerial photos as a faint coloration of the landscape. Balmat, who finished her thesis in June 2011, mapped the lineaments in the region between Chadron and the Black Hills and found the features to be faults in most cases. Many of the faults extend into so-called basement rocks — deep granite and schist similar to that exposed in the central Black Hills — at several miles depth.

According to the U.S. Geological Survey, the quake occurred Sunday at 11:51 p.m. at a depth of 3.1 miles and a magnitude of 3.7. At least five other earthquakes are known to have occurred near this same lineament. These quakes, which occurred between 1975 and 2009, had magnitudes between 3 and 4.

Faults are not well studied in Nebraska because they are poorly expressed at the surface. Balmat’s study, however, shows that they can be detected using simple tools such as satellite images. While well-defined lineaments in the Chadron area indicate earthquake-producing faults exist in the subsurface, chances these faults would cause even a moderate earthquake -- magnitude 5 or larger -- is extremely low, scientists say. But there are other reasons for studying faults.

“Identifying and studying faults in northwestern Nebraska and southwestern South Dakota is important not only for hazard assessment but also for understanding groundwater resources in the region,” Balmat said.