PRELIMINARY FINDINGS FROM RECENT GEOLOGIC MAPPING IN THE CENTRAL VIRGINIA SEISMIC ZONE

Identifying geologic structures that contribute to earthquakes in the Central Virginia Seismic Zone has been hampered by the lack of modern, detailed geologic mapping. Recent work in the aftermath of the August 2011 Louisa County earthquake is providing new insights about folds and faults that were unknown or only generally known in the area. The Quantico Synform, previously mapped as a simple structure in the area, appears to be more complex, with bifurcations, subsidiary folds, and cross-faults. The Lakeside and Little Fork Church faults, both of which have composite histories involving Paleozoic ductile compression and Mesozoic brittle extension, have been extended by new mapping northward to the Pendleton area. The trace of the Lakeside Fault is relatively straight, striking within a few degrees of N40E, over a distance of 80 km from near Curdsville in southern Buckingham County to near Buckner in Louisa County. The trace of the Little Fork Church Fault, while generally northeast-striking, is less linear, with segments striking from nearly north-south to nearly east-west. Both faults are marked by breccia zones, mylonite, and discontinuous bodies of mafic and ultramafic rock. Breccia zones also delineate several northwest-striking, unnamed brittle faults with apparently minor offset. While most of the recent seismicity can be attributed to faults west of the Lakeside and Little Fork Church faults, historic earthquake epicenters are spatially associated with both faults, indicating that they may still be seismically active.