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#           Shallow faulting and folding in the epicentral area of the 1886 Charleston, South Carolina, earthquake      

      March 6, 2022    

The moment magnitude (⁠Mw">Mw�w⁠) ∼7 earthquake that struck Charleston, South Carolina, on 31 August 1886 is the largest historical earthquake in the United States east of the Appalachian Mountains. The fault(s) that ruptured during this earthquake has never been conclusively identified, and conflicting fault models have been proposed. Here we interpret reprocessed seismic reflection profiles, reprocessed legacy aeromagnetic data, and newly collected ground penetrating radar (GPR) profiles to delineate faults deforming the Cretaceous and younger Atlantic Coastal Plain (ACP) strata in the epicentral area of the 1886 earthquake. The data show evidence for faults folding or vertically displacing ACP strata, including apparent displacements of near‐surface strata (upper ∼20 m). Aeromagnetic data show several northeast (NE)‐trending lineaments, two of which correlate with faults and folds with vertical displacements as great as 55 m on the seismic reflection and radar profiles. ACP strata show only minor thickness changes across these structures, indicating that much of the displacement postdates the shallowest well‐imaged ACP strata of Eocene age. Faults imaged on the seismic reflection profiles appear on GPR profiles to displace the erosional surface at the top of the upper Eocene to Oligocene Cooper Group, including where railroad tracks were bent during the 1886 earthquake. Some faults coincide with changes in river trends, bifurcations of river channels, and unusual river meanders that could be related to recent fault motion. In contrast to our interpreted NE fault trends, earthquake locations and some focal mechanisms in the modern seismic zone have been interpreted as defining a nearly north‐striking, west‐dipping zone of aftershocks from the 1886 earthquake. The relationship between the modern seismicity and the faults we image is therefore enigmatic. However, multiple faults in the area clearly have been active since the Eocene and deform strata in the upper 20 m, providing potential targets for field‐based geologic investigations.

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April 14, 2023

####                 Ground Penetrating Radar Profiles collected in Charleston, SC, in June 2015 for imaging shallow faults              

Earthquake Hazards Program

#### Thomas Pratt, Ph.D.

##### Research Geophysicist

Geologic Hazards Science Center

tpratt@usgs.gov

720-357-0470

#### Anjana K Shah

##### Research Geophysicist

Geology, Geophysics, and Geochemistry Science Center

ashah@usgs.gov

303-236-1218

#### J. Wright Horton, Jr., Ph.D.

##### Scientist Emeritus

Florence Bascom Geoscience Center

whorton@usgs.gov

703-648-6933

## Related Content

April 14, 2023

####                 Ground Penetrating Radar Profiles collected in Charleston, SC, in June 2015 for imaging shallow faults              

Earthquake Hazards Program

#### Thomas Pratt, Ph.D.

##### Research Geophysicist

Geologic Hazards Science Center

tpratt@usgs.gov

720-357-0470

#### Anjana K Shah

##### Research Geophysicist

Geology, Geophysics, and Geochemistry Science Center

ashah@usgs.gov

303-236-1218

#### J. Wright Horton, Jr., Ph.D.

##### Scientist Emeritus

Florence Bascom Geoscience Center

whorton@usgs.gov

703-648-6933

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#### Geology, Geophysics, and Geochemistry Science Center

West 6th Avenue and Kipling StreetDenver Federal Center Building 20Denver, CO80225United States

303-236-1800

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#### Geologic Hazards Science Center

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303-273-8500

####               Florence Bascom Geoscience Center          

12201 Sunrise Valley DriveReston, VA20192United States

703-648-5953

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