Geological Characterization of the Idalia Hill Fault Zone and Its Structural Association with the Commerce Geophysical Lineament, Idalia, Missouri

摘要

The Commerce geophysical lineament (CGL) is a 600-km-long, 5- to 10-km-wide, northeast-trending magnetic and gravity anomaly that extends from northeastern Arkansas to central Indiana. The seismogenic potential of the CGL is poorly known. However, recent geologic and geophysical studies along faults overlying the CGL support the notion that this prominent geophysical anomaly may be a source of future large-magnitude earthquakes in the central United States. Our geomorphic mapping, acquisition of seismic reflection, and ground-penetrating radar data, coupled with paleoseismic trenching and borehole information, collected at the South Holly Ridge site, near Idalia, Missouri, provide evidence of late Pleistocene to early Holocene deformation on the Idalia Hill fault zone. The Idalia Hill fault is a 0.5-km-wide zone of northeast-striking, near-vertical faults that directly overlie the CGL and coincide with the southeastern margin of the Bloomfield Hills. At the South Holly Ridge site, fault-related geomorphic features include a prominent, northeast- trending linear trough bounded on the southeast by a 2- to 3-m-high linear, north- facing escarpment and an apparent right-laterally deflected creek. These features, in turn, are aligned with regional northeast-trending linear valleys, escarpments, linear and deflected drainages, springs and bedrock notches mapped northeast and southwest of the site. Seismic reflection data across the Idalia Hill fault zone image near- vertical faults that displace Tertiary/Cretaceous and Tertiary/Quaternary reflectors and project upward to faults interpreted from ground-penetrating radar (GPR) surveys, and trench exposures. Together, these results suggest that deformation at the site is coincident with the CGL and is of primary tectonic origin.