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

LINKING TOPOGRAPHIC LINEAMENTS IN WESTERN NORTH CAROLINA TO ACTIVE FAULTS

Program: Late Breaking Session
Time: 3:45 PM – 4:05 PM

Authors

Abstract

There have been three earthquakes in western North Carolina with a magnitude greater than 5 in the past ~100 years: The M5.5 Skyland earthquake in 1916, the M5.2 Mitchell County earthquake in 1926, and the M5.1 earthquake near Sparta in 2020. Because the two early quakes were not well instrumented, we don’t know the precise epicenter locations, nor do we know which faults slipped. Existing geologic maps of these areas do not show any faults with recent movement. The 2020 Sparta earthquake resulted in numerous ground fissures as well as fault ruptures that define a discontinuous WNW-ESE zone of reverse and thrust faulting and ground deformation over a distance of about 3km, which is now known as the Little River fault (LRF). The mapped trace of the LRF corresponds in part to the zone of maximum displacement indicated by InSAR, which in turn is roughly parallel to a prominent NW-SE topographic lineament.

The earlier quakes also occurred near prominent lineaments that may be the surface expression of active faults. The 1926 earthquake was likely in southern Mitchell County, which is cut by the east-west Laurel Creek lineament. There have been several earthquakes on this lineament in the past 20 years including an M3.7 in 2005. The 1916 Skyland earthquake may have occurred on the Mills Gap fault, which corresponds to a WNW-ESE lineament and has evidence of Cenozoic movement. There are other similarly oriented lineaments in the Mills Gap area that may be associated with other Cenozoic faults.

Near Boone, NC, we documented the presence of a WNW-ESE brittle fault zone that we interpreted to be Cenozoic in age and seismically active. There were four magnitude 2.5-2.9 earthquakes ~2km south of the Boone fault in 2013 and 2014. Other earthquakes have been documented within a swarm of topographic lineaments that parallel the mapped trace of the Boone fault in a zone ~20km wide and ~180km long.

Before the Sparta earthquake, there were no documented earthquake fault ruptures in western North Carolina, and it was unclear which faults were producing earthquakes. The relationship between M5 earthquakes in North Carolina and prominent topographic lineaments may indicate that the lineaments are the surface expression of active faults.

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

doi: 10.1130/abs/2020AM-361228

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