SHALLOW FAULTING ON THE SOUTHEASTERN MARGIN OF THE REELFOOT RIFT OF WESTERN TENNESSEE

Previous interpretation of Dow Chemical petroleum exploration seismic reflection data has shown faulted Precambrian through lower Tertiary strata along the southeastern margin of the Reelfoot Rift in western Tennessee. In this current study 120 wireline logs, from 300 foot deep North American Coal Company wells, are used to map the shallow structure above these deep faults in southern Livingston, Tipton, and northern Shelby counties of southwestern Tennessee. Maps were drawn on the tops of the Eocene Cook Mountain and Memphis Sand. Three northeast-trending fault zones are identified. Reverse faulting of 25 meters or more and horsts are evident both from apparent displacement and repeated section in some wireline logs. Two of these fault zones were previously mapped in the Dow reflection data as flower structures in the deeper section. The third fault zone is similar in orientation and geometry to the other two, but is east of the seismic reflection coverage.

The westernmost fault zone extends south into Shelby County and probably continues under the Mississippi Alluvium into Arkansas. The middle of these fault zones appears to be the northward extension of the Memphis Fault; and the eastern most fault zone may be a northern extension of the Ellendale Fault. In addition to the northeast-trending faults, an east-trending down-to-the-north fault exists across southern Tipton County. All three of these northeast-trending fault zones appear to have generated some displacement of the Pliocene-Pleistocene Upland Gravel and thus have Quaternary activity.

Microseismic activity is occurring on the basement faults along the southeastern margin of the Reelfoot rift in Tipton County. Continuity of the deep seismogenic faults with the near-surface Quaternary faults along this rift margin has broad implications for seismic hazard assessment in western Tennessee and the metropolitan area of Memphis in particular.