EXAMPLES OF HIGH-RESOLUTION SEISMIC-IMAGING OF NEAR-SURFACE DEFORMATION WITHIN THE VERTICAL PROJECTION OF THE COMMERCE GEOPHYSICAL LINEAMENT, SE MISSOURI TO SW ILLINOIS

The Commerce geophysical lineament (CGL), approximately 50 km northwest and roughly parallel to the New Madrid seismic zone (NMSZ), is a 5- to- 10- km wide zone of near-linear, northeast-trending magnetic and gravity anomalies traceable in the basement for 600+ km across NE Arkansas, SE Missouri and SW Illinois. Scattered paleoliquifaction features, near-linear topographic trends, anomalous changes in drainage trends, mapped fault segments, and patches of modern seismicity are present along the vertical projection of the CGL. High-resolution seismic-reflection data acquired at several sites along a 200 km length of the Commerce geophysical lineament in southeast Missouri and SW Illinois image varying degrees of complexity with respect to faulting and post- Cretaceous to Quaternary strata deformation. On the southwestern end of a transect near Qulin, Missouri, approximately 20 m of apparent vertical displacement of Quaternary strata has occurred. Seismic-reflection data collected at Idalia Hill, Missouri (45 km to the northeast of Qulin) reveal a series of reverse and possibly right-lateral strike-slip faults with Quaternary displacement. In the Benton Hills region of Missouri, seismic data image a complicated series of shallow anticlines and synclines and fault-bounded blocks immediately north of the Commerce fault. At Wolf Creek, Illinois, approximately 20 km northeast of the Benton Hills, seismic and micro-gravity data reveal faults at or near the base of strikingly linear bluff fronts, faults with apparent Quaternary displacement and Paleozoic bedrock reflectors are more intensely deformed then at any other site. These data and geomorphic and surface-geologic evidence suggest: 1) the existence of at least one potential seismogenic structure(s) outside the currently active zone of modern New Madrid seismicity, and 2) the geographic location of the imaged deformation suggests that it is related to structure(s) associated with the deep-seated Commerce geophysical lineament.