Abstract View

Volume 32 Issue 3-4 (March-April 2022)

GSA Today

Article, p. 4-11 | Full Text | PDF

The Mw 5.1, 9 August 2020, Sparta Earthquake, North Carolina: The First Documented Seismic Surface Rupture in the Eastern United States

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