Geology topics

Research about Sparta, North Carolina

Source-linked reports with geographic coverage including Sparta, North Carolina.

4 recordsLinked to original sources

USGS2024

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

This field trip examines the results of integrated geologic studies of the 9 August 2020, M w 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 2 . The Little River fault is a thrust fault oriented 110–130°/45–70°SW, and mapped fault segments are en echelon with scarp heights from <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 (<50 ka). Surficial mapping identified several terrace deposits, including a deposit along Bledsoe Creek that yielded a 26 Al/ 10 Be 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. 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.

North Carolina↗

USGS2023

Preliminary map of the surface rupture from the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina—The Little River fault and other possible coseismic features

This publication is a preliminary map and geodatabase of the coseismic surface rupture and other coseismic features generated from the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina. Geologic mapping facilitated by analysis of post-earthquake quality level 0 to 1 lidar, document the coseismic surface rupture, named the Little River fault, and other coseismic features. The Little River fault is traced for approximately 4 kilometers and cuts the regional Paleozoic fabric (mean foliation, 063°/57°), and the dominant strike of joint sets are 0°–10°, 130°–150°, and 320°–340°. Individual fault strands occur in an en echelon pattern within an approximately 10-meter-wide zone. Trenches across the Little River fault document a thrust fault oriented 110°/45° with at least 10 centimeters (cm) of displacement. The Little River fault is marked by a flexure or scarp with a height of 5–30 cm and a local maximum height of 50 cm. Southwest-side-up displacement is consistent along the fault and indicates thrust kinematics. The strike of the Little River fault changes from 110° to 130° near Duncan Farm where it crosses Chestnut Grove Church Road (NC Rt. 1426). Although the surface expression of the fault terminates and (or) is imperceptible at both ends, deformation is still clear in residual surface maps showing the change between pre- and post-earthquake lidar elevations. Other coseismic features documented are rockfalls, ground cracks, fissures, lateral spreading on a sandbar, and mass-wasting scarps; several possible faults that were identified from lidar analyses strike E-W and oblique to the Little River fault.

North Carolina↗

USGS2022

Surface rupture on a secondary fault associated with the August 8, 2020, Mw 5.1 Sparta North Carolina Earthquake

On August 8, 2020 northwest North Carolina experienced a M w 5.1 earthquake that caused damage to buildings and roads in the city of Sparta. A regional centroid moment tensor solution shows the earthquake was the result of slip on a reverse fault with a minor strike-slip component. InSAR data, from the Japan Aerospace Exploration Agency’s ALOS2 satellite, reveal a deformation field that is more complex than expected from a single reverse fault earthquake. The data also reveal an apparent fault rupture at the Earth’s surface that caused damage to local roads. Modeling of the InSAR deformation field indicates the fault rupture is associated with a very shallow normal faulting event with an equivalent M w of about 5.1, that overprinted the reverse fault deformation field and possibly occurred aseismically.

North Carolina↗

USGS2022

The Mw 5.1 9 August 2020, Sparta earthquake, North Carolina: The first documented seismic surface rupture in the eastern United States

At 8:07 a.m. EDT on 9 Aug. 2020 a Mw 5.1 earthquake located ~3 km south of Sparta, North Carolina, USA, shook much of the eastern United States, producing the first documented surface rupture due to faulting east of the New Madrid seismic zone. The co-seismic surface rupture was identified along a 2-km-long traceable zone of predominantly reverse displacement, with folding and flexure generating a scarp averaging 8–10-cm-high with a maximum observed height of ~25 cm. Widespread deformation south of the main surface rupture includes cm-dm–long and mm-cm–wide fissures. Two trenches excavated across the surface rupture reveal that this earthquake propagated to the surface along a preexisting structure in the shallow bedrock, which had not been previously identified as an active fault. Surface ruptures by faulting are rarely reported for M <6 earthquakes, and hence the Sparta earthquake provides an opportunity to improve seismic hazard knowledge associated with these moderate events. Furthermore, this earthquake occurred in a very low strain rate intraplate setting, where earthquake surface deformation, regardless of magnitude, is sparse in time and rare to observe and characterize.

North Carolina↗