Keynote Speaker – Jesse S. Hill, Geohazards Geologist

Dr. Jesse S. Hill currently works for the North Carolina Geolog- ical Survey and is part of the landslide hazard mapping team based out of the Asheville regional office. He received a BS in Earth Sciences from Tennessee Technological University in 2011, and both an MS and PhD in geological sciences from the University of North Carolina at Chapel Hill in 2013 and 2018 respectively. His work centers on the structural geomorphology of the southern Appalachians, with a focus on the influences of post-orogenic structures on the landscape and slope stability.

Surface Rupture of the Little River fault in Response to the August 9, 2020 Mw 5.1 Earthquake near Sparta, North Carolina

Jesse S. Hill, Mark W. Carter2, Bart L. Cattanach1, Thomas J. Douglas1, Paula M. Figueiredo3, Eric Kirby4, David M. Korte11 Ashley S. Lynn4, Arthur J. Merschat2, Lewis A. Owen3, Corey M. Scheip1, Kevin G. Stewart4, Sarah B. Wells4, Anne C. Witt5, & Richard M. Wooten1 (1) North Carolina Geological Survey, (2) United States Geological Survey, (3) North Carolina State University (4) University of North Carolina at Chapel Hill, (5) Virginia Department of Mines, Minerals, and Energy

On August 9, 2020, an Mw 5.1 earthquake shook the Blue Ridge Mountains near Sparta, North Carolina, causing damage to over 500 buildings and other infrastructure. Surface ruptures are attributed to a SSW-dipping reverse fault, here named the Little River fault (LRF), and slide-related failures in anthropogenic fill. Field and unmanned aircraft systems assessments reveal multiple strands of the ESE-trending LRF spanning ~2.5 km across anthropogenically modified surfaces and underlying saprolite, and across open countryside. The LRF produced a vertical displacement of 25.2 cm between the ends of a 30-m- long building, with similar vertical displacements along much of the fault trace. The hanging wall was to the south where most of the infrastructure damage was located. A prominent scarp in an asphalt-covered road produced by the LRF allowed the geometry of the fault to be examined in detail, supplemented by trenching. The scarp had vertical displacements of 4.2–15.1 cm along a series of 6-m-traverses. Dilational cracks at the top of the scarp accommodated folding of the asphalt and opened oblique to the scarp trace, indicating a component of strike-slip motion, and are on average 0.45 cm wide and with an opening direction of 343°. The trench reveals coseismic horizontal shortening of 10 cm. The trench also shows evidence of mul- tiple earlier movements with ductile shear fabrics, brittle faults with dip-slip slickenlines, and fault gouge and breccia within weathered metasedimentary rocks of the Ashe Metamorphic Suite. Ages of previous fault deformation are undetermined, but we interpret the LRF as having reactivated during the August 9 event. Displacements projected onto the reverse fault plane within the trench had a strike azimuth of 100° and a dip of 45°S, with minor right-lateral motion, which matches slicken- lines along an older fault exposed in a trench near the eastern tip of one of the fault strands. Whether the LRF is the main 2020 earthquake causative fault is unclear. Although there is no recorded historical seismicity in and around Sparta, the LRF may be associated with the Giles County seismic zone, which is centered in Virginia about 100 km to the north. The ESE- trending fault trace parallels linear structures that cross the NE- trending southern Appalachian Blue Ridge such as the Boone and the Mills Gap faults, which both have evidence for Cenozoic deformation. The LRF, however, provides the first direct evidence of the surface rupture related to a recent earthquake in the southern Appalachian Blue Ridge.

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