Probabilistic Seismic Source Inversion of the 1886 Charleston, South Carolina, Earthquake from Macroseismic Evidence: A Major Updating

5 The source of the 1886 Charleston, South Carolina earthquake influences the computed seismic hazard of 6 the Southeastern U.S. and thus impacts public policy and engineering practice. However, because the 1886 7 rupture predated seismic instruments, its source is highly uncertain. This study presents probabilistic 8 seismic-source inversions of the Charleston earthquake from liquefaction evidence and historical intensity 9 reports. Using the latest predictive models and a novel inversion approach, we seek to constrain the 10 magnitude, location, and orientation of the 1886 rupture. Probability distributions of rupture magnitude are 11 conditioned on both the “Woodstock Fault” – a commonly inferred source of the 1886 event – and on an 12 unknown source, wherein the uncertainties of fault location and orientation are considered. These 13 distributions are compared to the M w 6.7-M w 7.5 distribution adopted by the U.S. National Seismic Hazard 14 Model Project (NSHMP). Collectively, the results do not provide strong support for the hypothesized 15 Woodstock Fault. This is not to say the Woodstock Fault does not exist, but rather, that the position of the 16 1886 source model cannot be constrained by the data and models studied herein, given the large 17 uncertainties inherent to each. While this is at odds with the underlying assumption of many prior studies, 18 the results nonetheless generally uphold the magnitude distribution assumed by the NSHMP. The largest 19 uncertainties inherent to this distribution are identified and could be diminished in the future. Finally, we 20 note that the inversion methodology used here is not specific to any region, or to certain types of evidence, 21 but can be applied to any seismic zone and to any co-seismic response. This methodology allows for 22 uncertainty to be accounted for in a more complete and transparent manner when inverting seismic source 23 parameters from macroseismic data. Of course, any limitations, biases, or unmodeled uncertainties inherent 24 to these data must be understood, and their implications acknowledged, as further discussed herein.