Source Characteristics of the 2020 Mw 5.1 Sparta, North Carolina, Earthquake Sequence
Description:
The Mw 5.1 Sparta, North Carolina earthquake on August 9, 2020 is the largest earthquake to occur in the Appalachian Blue Ridge province since 1916. It produced notable ground shaking and damage to infrastructure. Significantly, this moderate-magnitude event generated the first documented surface rupture due to faulting in the eastern United States. The ~2-km-long rupture occurred along a previously unmapped, ESE-striking, SSW-dipping reverse fault, now named the Little River fault. Detailed analyses of the earthquake sequence, including foreshocks, aftershocks, and the mainshock, provide critical insights into the mechanics of this intraplate event. Moment tensor inversion reveals a shallow (1 km depth) oblique reverse fault mechanism (strike N118°E, dip 52° SW) consistent with the observed surface deformation. Spectral analysis of the mainshock indicates an unusually low Brune stress drop (5.7 MPa) for an eastern U.S. earthquake, with a source radius of 1.5 km and average slip of 20 cm, both corroborating field observations. To improve hypocenter locations, we combine machine learning and template matching techniques to relocate over 1,000 events using a double-difference algorithm. The relocated seismicity delineates not only the NW-SE striking mainshock fault but also a conjugate NE-trending fault intersecting the primary structure near the northwest edge of the surface rupture. Further analysis of focal mechanisms and stress drop estimates for smaller events within the sequence will provide a more comprehensive understanding of the rupture process and its implications for seismic hazard assessment in this low strain rate tectonic setting.
Session: Earthquakes, Lithospheric Structure, and Dynamics in Stable Continental Region [Poster]
Type: Poster
Date: 4/17/2025
Presentation Time: 08:00 AM (local time)
Presenting Author: Qimin
Student Presenter: No
Invited Presentation:
Poster Number: 73
Authors
Qimin Wu Presenting Author Corresponding Author wu@lettisci.com Lettis Consultants International |
Martin Chapman mcc@vt.edu Virginia Polytechnic Institute and State University |
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Source Characteristics of the 2020 Mw 5.1 Sparta, North Carolina, Earthquake Sequence
Category
Earthquakes, Lithospheric Structure, and Dynamics in Stable Continental Regions