Current Understanding of Intraplate Seismicity and Surface Deformation Associated with the August 9th, 2020 Mw 5.1 Earthquake Near Sparta, North Carolina

Wednesday, 28 October 2020
1:30 PM - 5:30 PM
Auditorium

STATE OF STRESS AND SEISMOTECTONICS IN THE VICINITY OF THE 9 AUGUST 2020 MW5.1 SPARTA, NORTH CAROLINA, EARTHQUAKE

Program: Late Breaking Session
Time: 4:05 PM – 4:25 PM

Authors

Abstract

A MW5.1 earthquake occurred on 9 August 2020 near the town of Sparta, in northwest North Carolina, and within the southeastern part of the Appalachian Mountains. As we show based on our recently published new-generation stress map of North America (Lund Snee, J.-E., and Zoback, M.D., 2020, Multiscale variations of the crustal stress field throughout North America: Nature Communications, v. 11, 9 p., doi:10.1038/s41467-020-15841-5), the event occurred in a transitional strike-slip/reverse faulting stress field (Aϕ ≈ 1.8). The USGS focal mechanism indicates oblique reverse slip along a 48°- or 59°-dipping plane striking either ~N–S or ~NW–SE, respectively. This plane cuts across the regional structural grain but is consistent with the maximum horizontal principal stress (SHmax) in this area (oriented NE–SW to ENE–WSW). Published geologic and aeromagnetic maps show a structural grain defined by reverse faults, fold axes, dikes, metamorphic foliations, and boundaries between crustal basement domains, which all trend ~NE and are hence strongly oblique to the likely orientation of the causative fault. The compressive state of stress in this area may be related to drag along the bottom of the ~WSW-moving North American plate, as well as low gravitational potential energy related to a low geoid anomaly. Both mechanisms result in higher compressive stresses in the northeastern U.S. with respect to the mid-continent. More locally, the stress field could also be affected by compressive stress associated with relatively thin, potentially high-density crust along the Eastern Seaboard.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-361223

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.