EVALUATION OF FAULT ZONES IN THE ATLANTIC COASTAL PLAIN OF NORTH CAROLINA

The role of Cenozoic faulting in the geological development of the Atlantic Coastal Plain of North Carolina has been a topic of debate over several decades. Although the seismic hazard potential in the South Carolina coastal plain is well-established, the lack of a large earthquake in eastern North Carolina has limited interest in the Cenozoic tectonic history. Furthermore, previous studies documenting the structural geology and tectonism have been hampered by insufficient outcrop, drilling, and geophysical data. This study evaluates two previously defined fault systems, the Graingers fault zone (GFZ) and the East Coast fault system (ECFS) to assess the geomorphic and geophysical signatures in an effort to update the extent of these zones using digitized geophysical datasets and airborne LIDAR.

Data utilized in this study were aeromagnetic, gravity, and airborne-based LIDAR. Having these data in a digital, georeferenced format facilitates integration into GIS and allows comparison of the geophysical data with the high-resolution LIDAR. The GFZ can be traced in the aeromagnetic data as a northeast-southwest trending, linear magnetic high for ~100 km and defines the western margin of a magnetic and gravity low referred to as the Graingers basin. Speculation of a fault zone in this area in the 1950’s was suggested based on abrupt turns in the course of the Neuse River. The northeast trending segment of the river lies parallel to the magnetic high defining the GFZ. Additional topographic evidence of the GFZ is identified 40 km to the southwest along the Northeast Cape Fear River. Coincidence of the GFZ and outliers of Eocene Castle Hayne Formation may indicate fault control on the preservation of these rocks. The ECFS was previously defined as a ~600 km long, northeast-southwest zone that can be traced from South Carolina into Virginia. The ECFS in North Carolina occurs in the innermost coastal plain close to the Fall Zone and is along trend with a cluster of documented Cenozoic faults between the Neuse and Tar Rivers. Of the two segments of the ECFS defined in North Carolina, the ~75 km long northern segment appears to align with northeast-southwest trending magnetic highs, but there is not as strong a correlation between geomorphic and geophysical signatures as is observed with the GFZ.