Abstract

The northernmost extent of the New Madrid seismic zone in the central USA has been investigated using an integrated approach involving both compressional-wave (P) and horizontally polarized-wave (SH) seismic reflection and regional and dedicated borehole geophysical information in order to assess seismic hazard and risk. Our study area, centered around southernmost Illinois and western Kentucky, USA, represents an area of concentrated facilities (e.g., lock and dam sites and chemical plants on the Ohio River near its confluence with the Mississippi River) as well as an area of high potential soil amplification due to earthquake shaking. Integrated high-resolution seismic reflection profiles were used to investigate deformation in Mississippi embayment sediments localized over Paleozoic bedrock faults. A major zone of faulting (Olmsted fault) is identified from combined P-wave and SH-wave seismic profiles and from borehole data. Lower resolution, but deeper penetration, P-wave reflection profiles identify fault disruption of Paleozoic bedrock and disruption of Cretaceous and Tertiary stratal markers. Higher resolution, but shallower penetration, SH-wave images show deformation of Wisconsin till at the base of the Quaternary section that has propagated upward from bedrock faults. A northeast trend, parallel to New Madrid zone seismicity patterns, of faulting is observed with mainly normal faults that appear to dip to the northwest. Also observed are reverse faults and positive flower structures associated with a possible right-lateral strike-slip deformation that would be expected from seismicity patterns. The tectonic history deduced from the sum of geological and geophysical information indicates that faulting began in the Cretaceous accompanied by an over-thickening of the Cretaceous strata (McNairy Formation) in a locally subsiding structure bounded by the Olmsted fault, followed by lesser amounts of displacement near the base of the Holocene. Comparison of our geological structural information with recent earthquake data suggests that deformation in this critical region is ongoing.

Degree

MS

College and Department

Computational, Mathematical, and Physical Sciences; Geological Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2024-5

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd13442

Keywords

Olmsted fault, Illinois, New Madrid seismic zone, compressional-wave seismic reflection, horizontally polarized-wave seismic reflection, borehole data

Language

English

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