Mark W. Carter Ashley S. Lynn Kevin G. Stewart Paula Figueiredo William E. Odom Ryan J. McAleer Jorge A. Vazquez Nicholas Edwin Powell Christopher S. Holm-Denoma Arthur J. Merschat Mark W. Carter Arthur J. Merschat 2024 <p>This field trip examines the results of integrated geologic studies of the 9 August 2020, M_w<span>&nbsp;</span>5.1 earthquake near Sparta, North Carolina, USA. The earthquake generated ~4 km of coseismic surface rupture of the Little River fault and uplifted a surface area of ~11 km^{<strong>2</strong>}. The Little River fault is a thrust fault oriented 110–130°/45–70°SW, and mapped fault segments are<span>&nbsp;</span><i>en echelon</i><span>&nbsp;</span>with scarp heights from &lt;5–30 cm. The epicenter is in polydeformed rocks of the Ashe and Alligator Back Metamorphic Suites in the eastern Blue Ridge. Bedrock structure formed during multiple Paleozoic orogenies; the regional foliation strikes NE-SW and dips SE (mean orientation 063°/52°SE). Mapping identified late Paleozoic veins and shear zones, a regional joint set striking 330–340° and 250–240°, and brittle faults that cut the Paleozoic foliation. Brittle faults oriented similar to the Little River fault are mapped up to 4 km along strike from the coseismic rupture along Bledsoe Creek valley, and the combined length of the Little River fault system is ~8 km. Paleoseismic trenches across the Little River fault corroborate the reactivation of an older fault by the 2020 earthquake and reveal two events during late Pleistocene (&lt;50 ka). Surficial mapping identified several terrace deposits, including a deposit along Bledsoe Creek that yielded a<span>&nbsp;</span>²⁶Al/¹⁰Be isochron burial age of 0.46 ± 0.13 Ma and overlies a brittle fault, thus constraining the timing of movement of the fault at that location. Paleoliquefaction studies document soft-sediment deformation features in alluvium that may represent paleoseismic events. Collectively, these results highlight long-lived paleoseismicity of the Blue Ridge and that the 9 August 2020 earthquake reactivated an older, suitably oriented brittle fault in the bedrock. The Little River fault is an example of a previously unknown but active fault lying outside of known seismic zones with demonstrated recurrence of paleo-ruptures, raising questions about the assumption that damaging earthquakes are limited to areas of ongoing background seismicity, which is counter to seismic hazard assessments in the eastern United States.</p><p>Bedrock mapping separates eastern Blue Ridge lithostratigraphy of the Lynchburg Group and Ashe and Alligator Back Metamorphic Suites into separate fault-bound packages juxtaposed over various 1.3–1.0 Ga basement rocks of the northern French Broad massif by the Gossan Lead fault.</p> application/pdf 10.1130/2024.0067(03) en Geological Society of America Mesoproterozoic to Paleozoic tectonics, Pleistocene landforms, and Holocene seismicity in the Blue Ridge: Results from integrated studies of the 9 August 2020, Mw 5.1 earthquake area near Sparta, North Carolina, USA chapter