Abstract

Time-space patterns of seismicity with dimensions of several years and hundreds of kilometres can be identified in the southeastern United States from the available historic data. During the 15 yr preceding the 1886 earthquake, seismicity was low in South Carolina and high in the surrounding areas, forming a “doughnut” pattern. A protracted period of high seismicity followed the 1886 main shock. These “aftershocks” probably originated from a large area resembling the more recent South Carolina–Georgia seismic zone, rather than from the concentrated source in Charleston-Summerville, as indicated by available catalogues. These and other transient seismicity patterns in the southeastern United States suggest rapid and widespread stress changes and strain events which are mostly aseismic. Such events are not easily reconciled with an intraplate environment dominated by a low rate of overall strain, which, in the brittle part of Earth's crust, is produced by rare slip events on each of many scattered steeply dipping faults. They can, instead, be reconciled with movement on reactivated Appalachian low-angle thrusts or detachments of regional dimensions.

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