A Bounded Approach to Magnitude Estimation of the 1886 Charleston, SC Earthquake Based on Structural Analysis of Surviving Historic Buildings

摘要

Current seismic maps found in the International Building Code [1] used to design buildings in South Carolina include seismic hazard from a characteristic earthquake assigned a moment magnitude of M7.3. This magnitude represents an estimated magnitude of the 1886 Charleston, SC Earthquake. Although it is well established in South Carolina historical records that the 1886 Charleston, SC Earthquake caused significant damage to coastal South Carolina and was felt as far away as Wisconsin, previous research regarding magnitude estimates has focused on MMI assignments that contain large margins of uncertainty. As a result, current estimates vary from M6.8 to M7.3. The methodology for magnitude estimation presented in this paper includes an approach for estimating the magnitude of historic earthquakes that considers the pseudo dynamic analysis of significant buildings in Charleston, SC that survived the 1886 earthquake with well recorded damage, and using these results to back calculate the probable earthquake magnitude that would have caused such damage. Specifically, the finite element programs RISA-3D are used to perform linear and nonlinear pseudo dynamic analyses of two historic structures with upper and lower bounds placed on material properties and localized soil effects. Because the presented magnitude estimates are developed using an independent approach, they are valuable in terms of providing additional constraints for the MMI-based procedures. This paper presents upper and lower bound magnitude estimates for the 1886 Charleston, SC Earthquake based on pseudo dynamic structural analysis of the Miles Brewton House and Charleston City Hall. These two famous historic structures are both located in the historic district of Charleston, SC.