REELFOOT-ROUGH CREEK RIFT SYSTEM ANALOGS: FINDING NEW ANSWERS TO OLD QUESTIONS?

Although it is the seismogenic structures that are commonly the focus of seismic-hazard research, it should not be forgotten that these “active” structures are likely to be only part of a larger complex of “inactive” and unknown or unmapped structures. In attempting to answer questions concerning strain accumulation, structure reactivation, and crustal deformation, these processes must be considered as systemic and not isolated phenomena. In attempting to understand the whole-system response, it may be equally as important to consider which parts (structures) were inactive or locked as it is to know which parts were active or unlocked. Reelfoot-Rough Creek rift-system analogs from other continental rift settings may be, therefore, an important aid in interpreting whole-system response and in defining inactive and unknown structures.

An improved understanding of the geometry Reelfoot-Rough Creek rift system structures is necessary for accurate seismic hazard assessment in the central United States. Structural relationships observed in one system may yield new information about the geometry of structures in another system. In recent years a large number of multidisciplinary geophysical studies of ancient and modern rift systems worldwide have yielded a wealth of information on their structural, sedimentary, and tectonic histories. Although much has been learned about the Reelfoot-Rough Creek rift system, after nearly two decades of study, a variety of persistent questions remain. Among these are: 1) why are selected structures reactivated, 2) what is the true nature of the associated seismic potential, 3) what is the rate of regional strain accumulation, 4) how are the seismic source zones characterized, and 5) what are the mechanisms and spatial character of recent crustal deformation? Although the Reelfoot-Rough Creek rift is no longer an active extensional system, initial rift structures persist and some have been reactivated in the present-day regional compressional-stress environment. A greater understanding of the kinematics of the Reelfoot-Rough Creek rift system may be gained through an examination of structural configuration of other rift systems.