Aftershocks illuminate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from approximately 3 to 8 km in depth and are in a 1-km-thick zone striking approximately 036 degrees and dipping approximately 50 degrees SE, consistent with a 028 degrees , 50 degrees SE main-shock nodal plane having mostly reverse slip. This cluster extends approximately 10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician-Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, approximately 10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes approximately 035 degrees -039 degrees , and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks approximately 3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks approximately 1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.