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36°30'30"N Sparta ¯

36°30'0"N LOS -0.91- -0.50
-0.49- 0.00
0.01-1.00
1.01-2.00
36°29'30"N 2.01 -3.00

36°29'0"N

36°28'30"N

36°28'0"N 0 0.75 1.5 B 3 Km A

81°9'0"W 81°8'0"W 81°7'0"W 81°6'0"W 81°5'0"W 81°4'0"W
Canada
45°0'0"N 45°0'0"N

40°0'0"N 40°0'0"N Un Appalachian Mountains
United
States
St
35°0'0"N 35°0'0"N

Atlantic
°0'0"N °0'0"N Ocean

Me
C 25°0'0 25°0'0 Mexico D

80°0'0"W 70°0'0"W

Figure 1. Location, earthquake sequence, and interferometric synthetic aperture radar interferogram for the Sparta earthquake. (A) Unwrapped phase
interferogram overlaying a lidar-derived hillshade model with the main surface rupture (black line) and August 2020–February 2021 instrumental seismicity
(circles; USGS catalog). Topographic lineament marked by brown arrows. Figure 2 location denoted by the dashed white rectangle. Line P–P' indicates the
projection plane for seismicity. (B) Focal mechanism solution (Horton et al., 2021). (C) Projection of seismic sequence (USGS catalog) into a plane with azi-
muth N20°. (D) Location of the earthquake (red) in eastern North America, with North Carolina outlined. LOS—line of sight; CERI—Center for Earthquake
Research and Information, University of Memphis; SLEUC—Saint Louis University Earthquake Center.

www.geosociety.org/gsatoday 5