THREE DIMENSIONAL MODELING OF THE REELFOOT RIFT AND NEW MADRID SEISMIC ZONE

Geologic and geophysical data within the northeast-trending Reelfoot Rift and coincident New Madrid seismic zone of the northern Mississippi Embayment have been utilized to create a three dimensional software model of the region. The three-dimensional rendering promotes improved interpretations of the relationships between faults, earthquakes, and regional geology. The model permits projection of deep structures into the shallow stratigraphic section by incorporating the tops of the Precambrian, Paleozoic, Cretaceous, Tertiary units, faults, and earthquake foci. Integration of multiple datasets has better defined the Precambrian surface, improved fault delineation, and allowed the production of several possible fault models with increasing structural complexity. Previously mapped Proterozoic northwest striking faults have been incorporated into the model and are strongly correlated to changes in orientations of the rift margin faults and significant changes in the relief on the Precambrian surface. The location of the Reelfoot Rift western margin fault has been improved and extends north to the Reelfoot thrust fault. The two faults which form the eastern margin of the Reelfoot Rift have also been better mapped and one of the faults has been extended to Union City, Tennessee where it is expressed as a fault scarp.

The northeast-striking Axial fault of the Reelfoot Rift is well defined from seismic reflection data and earthquake foci. This Axial fault is a wide strike-slip zone that segments the northwest-striking and southwest-dipping Reelfoot thrust fault into two discrete fault planes. The two sections of the Reelfoot thrust were mapped using earthquake foci. These foci were utilized to create trend surfaces thereby providing more accurate strike/dip information, and refining fault locations and extents. There appears to be a significant down-to-the-southwest step in the Precambrian basement at the Reelfoot thrust, thus suggesting the thrust may be an inverted basement normal fault. The use of three-dimensional modeling of the region has improved our understanding and allowed greater interpretation of deep structures and their upsection propagation.