Over the last decade, several investigations have demonstrated a plausible link between surface and near-surface tectonic features and the vertical projection of the Commerce geophysical lineament (CGL), a 5- to 10-km-wide basement magnetic anomaly longer than 600+ km that extends from Arkansas through southeast Missouri and southern Illinois and into Indiana. Structural features interpreted from the Tamms, Illinois high-resolution seismic-reflection survey and supporting microgravity data correlate with anomalous changes in drainage patterns, strikingly linear topographic bluff-front scarps, and the complex faulting and folding of Paleozoic rock.

Post-Devonian displacement associated with the CGL is clearly identified in the Tamms area of southern Illinois. Several imaged faults are traceable to the Paleozoic/Quaternary interface, and, at one site, deformed Quaternary strata may have been faulted upward 5 to 10 m. Based upon the seismic-reflection and microgravity data provided within this paper, we believe that faults associated with the CGL need to be investigated further to determine their potential as hazardous seismic sources outside of the main zones of New Madrid seismicity.

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