Shallow Reflection Seismic Study Of Recent Faulting In The Benton Hills, Southeastern Missouri

During the summer of 1997, the Department of Geology and Geophysics at the University<br>of Missouri-Rolla conducted a high resolution shallow @IRS) reflection seismic study of the<br>Commerce Geophysical Lineament (CGL) both within and adjacent to the Benton Hills, southeast<br>Missouri. Our primary objective was to determine whether the CGL constitutes part of a late<br>Quaternary fault system located outside of the New Madrid area of active micro-seismicity. A<br>secondary objective was to demonstrate that the reflection seismic technique can be used to map the<br>shallow subsurface in an intensely faulted environment.<br>The reflection seismic study was successful. Our interpreted data demonstrate that the CGL<br>zone (both within and adjacent to the Benton Hills) is structurally complex - reflection seismic and<br>geologic data indicate extensive and episodic faulting of Paleozoic, Cretaceous, Tertiary, and<br>Quaternary strata. The individual faults exhibit significant near-vertical displacements, and appear<br>to be oriented north-northeast essentially paralleling the CGL.<br>These observations support the argument that the southeastern escarpment of the Benton<br>Hills is tectonic in origin, and indicate that the CGL constitutes part of a late Quaternary fault system<br>located outside of the New Madrid area of active micro-seismicity. This implies that earthquake risk<br>in southeast Missouri is greater than generally thought. This conclusion has important implications<br>for earthquake hazard assessment in the mid-west.