Abstract for AGU as submitted…oh 2 minutes ago?

September 2nd, 2010

Pervasive post-Eocene faulting and folding in unconsolidated sediments of the Mississippi River, Central U.S. as imaged by high-resolution CHIRP seismic data

Xenia Fave*, M. Beatrice Magnani**, Brian Waldron***, Kirk McIntosh****, Guo Lei**, Steffen Saustrup****

*Florida Institute of Technology, Melbourne, FL
**Center for Earthquake Research and Information, University of Memphis, Memphis, TN
***Ground Water Institute, University of Memphis, Memphis, TN
**** University of Texas at Austin Institute for Geophysics, Austin, TX

Despite being located in the stable continental interior of the North American plate, in 1811-1812 the New Madrid Seismic Zone (NMSZ) experienced among the largest magnitude historical earthquakes that ever occurred in the U.S. Paleoseismological evidence shows that large earthquakes have been occurring every 500 yr in the region for the past few thousand years, and historical and instrumental seismicity demonstrate that the NMSZ fault system is actively deforming today. By contrast, motion rates emerging from almost twenty years of geodetic observations substantiate a very slow rate of deformation across the NMSZ faults, suggesting that present velocities are not representative of the long-term deformation rate of the NMSZ fault system, and that deformation has likely been accommodated along structures additional to the NMSZ.

In the summer of 2010, a high-resolution marine seismic reflection survey was carried out along the Mississippi River as part of a multi-year cooperative effort to investigate the spatial and temporal distribution of deformation in the Mississippi Embayment. Coincident to the seismic reflection profile, the survey also acquired ~300 km of CHIRP (Edgetech SB-512i) data from Cape Girardeau, MO to Caruthersville, MO. The CHIRP used a 0.7-1.2 kHz source pulse and recorded to a depth of 5-50 m sub-bottom. Here we present the preliminary interpretation of part of the CHIRP profile along the Mississippi River north of Hickman, KY, where the survey imaged a highly reflective sedimentary package down to a depth of ~50 m. The sedimentary sequence is about 20 m thick and appears to be bounded at the top and at the bottom by angular unconformities. The package is mildly folded and pervasively faulted, in some cases by extensional faults that exhibit up to 2 m of displacement and that reach the riverbed.
Based on exposure of Eocene deposits 7 km to the east of the study area, and on the correlation of electric and gamma logs of nearby oil, gas and water wells, projected from 12 km to the west and which penetrated the Eocene units at a depth of 67 m, we determined that the reflective package corresponds to one of the elements of the Jackson Fm, (i.e. the top of the Eocene and of the Tertiary sequences), sealed at the top by the basal unconformity of the Mississippi River Quaternary alluvium and at the bottom by the Claiborne Group deposits.