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.