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The 1886 Charleston, South Carolina, Earthquake: Source Properties and Ground Motions

The 1886 Charleston, South Carolina, earthquake was felt over much of the eastern United States, with magnitude 6.8-7.3 previously estimated from felt reports. In spite of extensive contemporaneous documentation, the earthquake and Charleston Seismic Zone have remained enigmatic. Bilham and Hough (TSR, 2023) recently developed an elastic deformation model for the 1886 earthquake using identified geodetic constraints, including a ~4.5-m dextral offset in a railroad line southeast of Summerville where the track crosses the previously mapped Summerville fault. The offset was described in contemporary accounts but never considered by subsequent studies. Unlike other railroad disturbances in the epicentral region it cannot be explained by site response. The preferred deformation model yields moment magnitude 7.3, but in contrast to conclusions of previous studies, we found no support for significant slip south of the Ashley River. We also revisited the near- and far-field intensity distribution using extensive archival accounts. We compare the intensity distribution, constrained at nearly 1300 locations, with predictions from modern ground motion models (GMMs) and ground motion-intensity conversion equations. Although GMMs are characterized by significant epistemic uncertainty for large earthquakes, we show that the intensity distribution is consistent with average model predictions, assuming Mw 7.3. Given the complex influence of site response on saturated Atlantic Coastal Plain (ACP) sediments throughout the epicentral region, the fit to near-field intensities is insensitive to the rupture length or other detailed rupture properties. Macroseismic intensities can be used together with model predictions to improve a ShakeMap for the earthquake, but cannot improve the independently determined rupture model or Mw. An apparent concentration of high intensities near Rantowles, west of Charleston, was defined by a multiplicity of environment effects that are readily explained by dynamic stress effects and site response on saturated ACP sediments prevalent throughout the low-lying marshy regions surrounding Charleston.

Session: Tectonics and Seismicity of Stable Continental Interiors [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Susan Hough

Student Presenter: No

Additional Authors