High-resolution shallow seismic reflection profiles across the northwesternmost part of the New Madrid seismic zone (NMSZ) and northwestern margin of the Reelfoot rift, near the confluence of the Ohio and Mississippi Rivers in the northern Mississippi embayment, reveal intense structural deformation that apparently took place during the late Paleozoic and/or Mesozoic up to near the end of the Cretaceous Period. The seismic profiles were sited on both sides of the northeast-trending Olmsted fault, defined by varying elevations of the top of Mississippian (locally base of Cretaceous) bedrock. The trend of this fault is close to and parallel with an unusually straight segment of the Ohio River and is approximately on trend with the westernmost of two groups of northeast-aligned epicenters ("prongs") in the NMSZ. Initially suspected on the basis of pre-existing borehole data, the deformation along the fault has been confirmed by four seismic reflection profiles, combined with some new information from drilling. The new data reveal (1) many high-angle normal and reverse faults expressed as narrow grabens and anticlines (suggesting both extensional and compressional regimes) that involved the largest displacements during the late Cretaceous (McNairy); (2) a different style of deformation involving probably more horizontal displacements (i.e., thrusting) that occurred at the end of this phase near the end of McNairy deposition, with some fault offsets of Paleocene and younger units; (3) zones of steeply dipping faults that bound chaotic blocks similar to that observed previously from the nearby Commerce geophysical lineament (CGL); and (4) complex internal deformation stratigraphically restricted to the McNairy, suggestive of major sediment liquefaction or landsliding. Our results thus confirm the prevalence of complex Cretaceous deformations continuing up into Tertiary strata near the northern terminus of the NMSZ.
|Number of pages||21|
|State||Published - Jun 26 2003|
Bibliographical noteFunding Information:
This research was supported, in part, by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number 01HQGRO126 (University of Illinois) as part of the National Earthquake Hazards Reduction Program (NEHRP). The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. This work was also supported in part by the Earthquake Engineering Research Centers Program of the National Science Foundation under Award Number EEC-9701785. We express our appreciation to Nick Niestrath, County Engineer for Pulaski, IL for the assistance in using county roads for the seismic surveys and to personnel of the U.S. Army Corps of Engineers at Lock and Dam 53 for allowing us to use their facility as a staging area for the surveys in Illinois. We are also grateful to the Kentucky Department of Fish and Wildlife Resources for allowing access to the Ballard Wildlife Management Area. Reviews of previous versions of this report by C. Juhlin and R.B. Van Arsdale substantially improved the final version. We thank W.J. Stephenson for supplying Fig. 11 .
- Seismic reflection
ASJC Scopus subject areas
- Earth-Surface Processes