Mesozoic and Cenozoic Faulting Imaged at the Epicenter of the 1886 Charleston, South Carolina, Earthquake

Abstract

A seismic reflection profile collected in 1981 southeast of Summerville, South Carolina, was reprocessed to investigate the recent observation of unusual features. The reprocessing included geometrical spreading and attenuation correction, minimum-phase filtering, and spiking deconvolution, which led to improved velocity analysis and residual static correction. The result gives an improved image of the shallow crust in the epicentral area of the 1886 Charleston earthquake. There is clear evidence of a down-to-the-east steeply dipping fault with approximately 200 m of vertical offset, displacing lower Mesozoic sedimentary and volcanic rocks. Diffraction from fault edges is responsible for the observation of unusual events with abnormal move-out, which led to the discovery of the faulting. The overlying Cretaceous and Tertiary sedimentary section shows approximately 10 m of reverse up-to-the-east displacement, resolved by the data to within 100 m of the ground surface. Two other near-vertical faults with down-to-the east offset of lower Mesozoic units are inferred from the data immediately to the northwest of the major fault. The locality is on the north side of the Ashley River, near the place known as Gregg’s Landing, and it coincides with the epicenters of modern seismic activity and maximum shaking effects documented in 1886. The Charleston earthquake was very likely associated with this faulting.