The 1886 Charleston, South Carolina, Earthquake: Intensities and Ground Motions

The 1 September 1886 Charleston, South Carolina, earthquake was one of the largest preinstrumental earthquakes in eastern North America for which extensive contemporaneous observations were documented. The distribution of shaking was mapped shortly after the earthquake, and reconsidered by several authors in the late twentieth century, but has not been reconsidered with a modern appreciation for issues associated with macroseismic data interpretation. Detailed contemporary accounts have also never been used to map the distribution of numerical shaking intensities in the near field. In this study we reconsider macroseismic data from far‐field accounts as well as detailed accounts of damage in the near field, estimating modified Mercalli intensity values at 1297 locations including over 200 definite “not felt” reports that delineate the overall felt extent. We compare the results to the suite of ground‐motion models for eastern North America selected by the National Seismic Hazard Model, using a recently proposed mainshock rupture model and an average site condition for the locations at which intensities are estimated. The comparison supports the moment magnitude estimate, 7.3, from a recently proposed rupture model (Bilham and Hough, 2023). A ShakeMap constrained by model predictions and estimated intensities further illustrates this consistency, which we show is insensitive to rupture model details. Given the uncertainty of calibration relations for magnitudes close to 7, the overall intensity distribution provides a good characterization of shaking but cannot improve the independent moment magnitude estimate. We also identify a previously unrecognized early large aftershock that occurred 9–10 min after the mainshock, for which we estimate magnitude ∼5.6.

All data used in this study are from published sources. Detailed macroseismic accounts are included in Dutton (1890), available at https://digital.tcl.sc.edu/digital/collection/quake/id/955/ (last accessed July 2023). Additional photographs are available at https://www.eas.slu.edu/eqc/eqc_photos/1886EQ/ (last accessed July 2023). In the supplemental material (Table S1) we summarize available data along with published interpretations (intensities) and interpretations by this study. In Table 1 we summarize near‐field data from sources indicated. Through the twentieth century, the United States Earthquakes series was published by the U.S. Coast and Geodetic Survey. These volumes are widely available online, and can be located using https://WorldCat.org (last accessed November 2023). Historical newspaper holdings can also be explored using https://WorldCat.org (last accessed November 2023). 1 and 10m digital elevation models were downloaded from https://www.opentopography.org (last accessed June 2023).

Supplementary data

The authors acknowledge that there are no conflicts of interest recorded.