The 2020 Mw 5.1 Sparta, North Carolina, Usa Earthquake: Surface Deformation and Paleoseismicity of the Little River Fault
Description:
The Mw 5.1 2020 earthquake near Sparta, North Carolina, was a shallow oblique reverse earthquake with a surface rupture, the first documented in the eastern U.S. This was an unexpected event because: 1) the WNW trending Little River fault was previously unknown, and 2) a surface rupture generally is not expected from an Mw5.1 earthquake. Initial surveys recognized a 2-km-long surface rupture with topographic steps trending ~N110°. Reverse scarps and associated folding of the uplifted southern hanging wall were recognized during initial field surveys, consistent with an oblique-reverse focal mechanism and N108°-striking 60° SW-dipping nodal plane. Although no lateral displacement was recognized along the rupture trace, post-earthquake surveys of geodetic monuments corroborated an off-fault left-lateral displacement. A post-earthquake lidar revealed an additional ~2.5 km of surface rupture and helped recognize additional vertical deformation expressed by a wider folding of the hanging wall leading to recognize a larger co-seismic deformation area.
To further investigate the fault zone, we conducted ground-penetrating radar (GPR) and electrical resistivity surveys at favorable locations across the rupture trace. Results highlighted a 10-15 m wide fault zone, and GPR showed south-dipping reflectors. Combined geophysics and geomorphology guided site selection for paleoseismic trenching. At two trenches, a sequence of Quaternary soil and colluvium overlaying the weathered bedrock was deformed by several WNW-NW fault strands in a complex, 15-m-wide fault zone. The 2020 rupture was accommodated by three reverse strands, with a total along-fault dip-slip of ~50 cm, associated with a ~30 cm high scarp. An upper Bt soil horizon of probable Late Pleistocene age has a cumulative displacement of ~1 m, providing evidence for previous surface ruptures. The Little River fault is an example of a previously unknown but active fault lying outside of known seismic zones, raising the question of how many similar, unknown faults pose a seismic hazard to the eastern U.S.
Session: Tectonics and Seismicity of Stable Continental Interiors
Type: Oral
Date: 4/19/2023
Presentation Time: 02:30 PM (local time)
Presenting Author: Paula M. Figueiredo
Student Presenter: No
Invited Presentation: Yes
Authors
Paula Figueiredo Presenting Author Corresponding Author paula_figueiredo@ncsu.edu North Carolina State University |
DelWayne Bohnenstiehl drbohnen@ncsu.edu North Carolina State University |
Arthur Merschat amerschat@usgs.gov U.S. Geological Survey |
Mark Carter mcarter@usgs.gov U.S. Geological Survey |
Eric Szimansky szymaner@umich.edu University of Michigan |
Karl Wegmann karl_wegmann@ncsu.edu North Carolina State University |
Lewis Owen lewis.owen@ncsu.edu North Carolina State University |
Matthew Ricker mcricker@ncsu.edu North Carolina State University |
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The 2020 Mw 5.1 Sparta, North Carolina, Usa Earthquake: Surface Deformation and Paleoseismicity of the Little River Fault
Category
Tectonics and Seismicity of Stable Continental Interiors