Paula M. Figueiredo
Dept. of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North
Carolina 27695, USA
Jesse S. Hill
North Carolina Geological Survey, Swannanoa, North Carolina 28778, USA
Arthur J. Merschat
U.S. Geological Survey, Florence Bascom Geoscience Center, Reston, Virginia 20192, USA
Corey M. Scheip
Dept. of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North
Carolina 27695, USA, and North Carolina Geological Survey, Swannanoa, North Carolina 28778, USA
Kevin G. Stewart
Dept. of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North
Carolina 27599, USA
Lewis A. Owen
Dept. of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North
Carolina 27695, USA
Richard M. Wooten
North Carolina Geological Survey, Swannanoa, North Carolina 28778, USA
Mark W. Carter
U.S. Geological Survey, Florence Bascom Geoscience Center, Reston, Virginia 20192, USA
Eric Szymanski
Dept. of Earth and Environmental Sciences, University of Michigan, Michigan 48109, USA
Stephen P. Horton
Center for Earthquake Research and Information, The University of Memphis, Memphis, Tennessee
38152, USA
Karl W. Wegmann
Dept. of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North
Carolina 27695, USA, and Center for Geospatial Analytics, North Carolina State University,
Raleigh, North Carolina 27695, USA
DelWayne R. Bohnenstiehl
Dept. of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North
Carolina 27695, USA, and Center for Geospatial Analytics, North Carolina State University,
Raleigh, North Carolina 27695, USA
Gary W. Thompson
North Carolina Geodetic Survey, Raleigh, North Carolina 27607, USA
Anne Witt
Virginia Dept. of Mines, Minerals and Energy, Virginia 22903, USA
Bart Cattanach
Thomas Douglas, North Carolina Geological Survey, Swannanoa, North Carolina 28778, USA
Abstract
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.
Manuscript received 4 June 2021. Revised manuscript received 4 Jan. 2022.
Manuscript accepted 5 Jan. 2022. Posted 26 Jan. 2022.
© The Geological Society of America, 2022. CC-BY-NC.
https://doi.org/10.1130/GSATG517A.1