Intraplate seismicity and stress in the southeastern United States

Abstract

The stress induced by topography and by density heterogeneities in the lithosphere has been computed for two seismic regions in the southeastern United States: the Southern Appalachian mountains and the South Carolina Coastal Plain. The lithosphere was assumed to be a three-dimensional layered elastic slab overlying an inviscid fluid. The calculations indicate that the local stress is of the same magnitude as the tectonic stress (tens of MPa); but contradictory conclusions are suggested by the comparison of stress differences and principal directions with earthquake locations and focal mechanisms. In the Southern Appalachians, the seismicity correlates well with the stress maximum and focal mechanisms agree with the calculations where regional stress is combined with locally induced stress. In South Carolina, a combination of regional and local stress can explain the orientation of focal mechanisms, but stress does not concentrate in the region of Charleston, and, thus, other factors must play a role in the Charleston seismicity.