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Exploring Rupture Models for the 1 September, 1886, Charleston, South Carolina, Earthquake

Description: 

The 1 September 1886 Charleston, South Carolina, earthquake was one of the largest pre-instrumental earthquakes in eastern North America for which extensive contemporaneous observations were documented. The source zone has, however, remained enigmatic, with evidence of the rupture and faulting obscured by saturated Atlantic Coastal Plains sediments. We considered detailed archival accounts, including documented disruption to railroad lines through the epicentral region. The most severe disruptions of the tracks occurred south of the town of Summerville. The railroads have long since been repaired and are now generally straight to within 30 cm over distances of tens of km. However, GPS measurements reveal the railroad alignment south of Summerville has a ≈3 m dextral offset that is reasonably interpreted as a quantitative measure of coseismic surface deformation. We use these data together with present-day surface morphology and other constraints to develop elastic deformation models based on previously proposed faults in the region. Of possible scenarios, evidence favors >4 m of reverse slip on a ≈30-km-long blind rupture parallel to the North Woodstock fault (Talwani and Dura-Gomez, 2009) but with ≈45° westward dip similar to the reverse fault proposed by Chapman et al. (2016), intersecting the surface near the east-facing Summerville scarp. In our model, dextral slip occurs on secondary shallow faults above this thrust plane. A common feature of models for the 1886 earthquake is the absence of significant coseismic rupture south of the Ashley River. In the near-field region, from Summerville to Charleston, damage was exacerbated by extensive liquefaction on saturated fluvial, barrier sand, and marsh facies. Our preferred scenario implies a moment magnitude of M 7.1, consistent with estimates from previous studies. Given the strong dependence of radiated energy on stress drop, however, any intensity-based magnitude will provide at best a weak constraint on M.

Session: Tectonics and Seismicity of Stable Continental Interiors

Type: Oral

Date: 4/19/2023

Presentation Time: 05:30 PM (local time)

Presenting Author: Susan E. Hough

Student Presenter: No

Invited Presentation: 

Authors