Rift Basins and Intraplate Earthquakes: New High-Resolution Aeromagnetic Data Provide Insights Into Buried Structures of the Charleston, South Carolina Seismic Zone

Abstract

The delineation of faults that pose seismic risk in intraplate seismic zones and the mapping of features associated with failed rift basins can help our understanding of links between the two. We use new high-resolution aeromagnetic data, previous borehole sample information, and reprocessed seismic reflection profiles to image subsurface structures and evaluate recent fault activity within the Charleston seismic zone, the associated Mesozoic South Georgia rift basin, and surrounds. The new aeromagnetic data provide an unprecedented view of buried basement structures. NE- and NW-trending lineaments of various lengths throughout the survey area are interpreted as Paleozoic orogenic structures and Mesozoic dikes, respectively. Within the rift basin, 15- to 20-km long ESE-trending lineaments are associated with faults in pre-Cretaceous strata of the reflection data and are interpreted as Mesozoic rift structures. Various intersections and terminations of interpreted faults suggest rift-related reactivation of Paleozoic faults and corresponding inheritance for Mesozoic structures. The reflection data show that several Paleozoic and Mesozoic faults are associated with deformation in Cretaceous and younger sediments, suggesting reactivation in the more recent passive margin setting. Two of these faults, one NE-striking and one ESE-striking, are coincident with surficial landforms, suggesting Quaternary slip; the ESE-striking fault is also well-aligned with a plan-view offset in modern seismicity. A favorable orientation for reverse motion on ESE-striking Mesozoic faults, a possible sub-basin, and potentially weakened lithosphere are failed rift basin features that may influence intraplate seismicity within the Charleston seismic zone.