STRIKE SLIP ON REACTIVATED TRIASSIC(? ) BASIN BOUNDARY FAULT ZONES AS SOURCES OF EARTHQUAKES NEAR CHARLESTON, S. C.

Interpretation of several thousand kilometers of multifold seismic reflection data supports the old theory that earthquakes in the Charleston, S. C. area are associated with reactivated Triassic(? ) basin boundary extensional fault zones. The Gants-Cooke fault zone associated with the Jedburg basin in the 1886 meizoseismal area, an unnamed fault along the margin of the Branchville basin in the Bowman earthquake area and the offshore Helena Banks fault zone (no observed seismicity) along the margin of the Kiawah basin show evidence of reactivation of Triassic(? ) normal faults zones in a compressional, probably strike slip sense. The previously reported reverse separation of these faults observed on the seismic profiles in the late Cretaceous-Cenozoic Coastal Plain sediments is possibly produced by oblique slip with the horizontal component possibly 10 to 100 times the vertical. Earthquake recurrence intervals of several thousand years reported in the Charleston area appear consistent with ranges of magnitude of strike slip displacement inferred from the seismic reflection data, and are constrained by aeromagnetic data.