Year of Publication

2021

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

First Advisor

Dr. Edward W. Woolery

Abstract

The New Madrid Seismic Zone (NMSZ) is a large source of seismic hazard within the central and eastern United States. Seismogenic source parameters such as active fault location, slip rate, total displacement, and strain accommodation is poorly constrained due to the masking effect of the Mississippi Embayment sediment and agricultural practices on structures and surface expressions. Consequently, noninvasive geologic and geophysical investigation of the subsurface is needed to characterize seismogenic sources. Recent investigation of the Reelfoot Fault found that there is a strain accommodation enigma between the dextral offset at seismogenic depth versus the surface expression, Reelfoot Scarp. This strain imbalance was suggested to be due to a dextral shear zone from a splayed portion of the Axial Fault continuing through Reelfoot Fault to the northeast. Seismic reflection surveys collected at Sassafras Ridge, 12 km to the northeast of Reelfoot Fault, found a dextral transpressional structure in Paleozoic to Eocene horizons. This structure was suggested to be an extension of the shear zone to the northeast of Reelfoot Fault but could not satisfy temporal boundary conditions due to the lack of resolution in the upper 50 m. New, near-surface seismic reflection surveys were collected at Sassafras Ridge, targeting the basal Quaternary gravel and intra-Quaternary sediments. The resultant images showed steeply dipping northeast striking faults with vertically offset and arched Quaternary reflectors, extending within 5 m of the surface. There are five imaged transpressional faults within two zones of deformation, forming an $\sim$600 m wide flower structure, with vertical displacements of 9 m and 4 m at the top of the Quaternary basal gravel, and top of the intra-Quaternary coarse sands, respectively. The seismic images were correlated with LiDAR digital terrain analysis and an electrical resistivity survey to characterize the near-surface extent of these faults. The results suggest that the transpressional flower structure imaged across Paleozoic to Quaternary reflectors extends to the surface and is expressed as a lineament spanning the length of Sassafras Ridge observed in LiDAR slope and roughness maps. These results provide further evidence for the hypothesized shear accommodation fault across the Reelfoot Fault, as well as identifying a previously unknown Quaternary-active fault in westernmost Kentucky, northeast of the most active parts of the NMSZ.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.397

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