Author ORCID Identifier

https://orcid.org/0009-0009-1321-6701

Date Available

12-20-2023

Year of Publication

2023

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department/School/Program

Geology

First Advisor

Dr. Seth Carpenter

Abstract

Due to the nature of the Mississippi Embayment region and its vicinity to the New Madrid Seismic Zone, earthquake ground-motion site effects are potential hazards and quantifying the associated hazard is a necessary step for public safety. Measuring the Vs contrast between bedrock and overlying soil layers is necessary for site effect evaluation. Various methodologies for investigating shear wave velocity (Vs) profiles have been implemented in the Mississippi Embayment. However, these previous studies provided a wide range of bedrock Vs. In this study, microtremor array measurements, utilizing ambient background noise, were used to provide an additional estimate of the bedrock Vs at the Vertical Seismic Array at Paducah (VSAP) from the recordings of 17 SmartSolo 5 Hz, 3 component geophones arranged in a nested triangle array. H/V spectral ratios were also calculated. Geopsy was then used to produce dispersion curves via MSPAC and FK analyses, which were then inverted using Dinver. A joint inversion was also performed using the fundamental frequency (f0) and the dispersion curves from the MSPAC and FK analyses. Using misfits and the bounded Vs in velocity profiles as measures of model reliability, modeled shear wave velocity (Vs) profiles were developed from the surface to the limestone bedrock at 100 m depth. Bedrock Vs of the Warsaw limestone was estimated using three different preliminary Vs models from previous studies for the dispersion curve inversions. Allowing the Vs of each layer to become bounded by low misfit models resulted in three different Vs profiles. Bedrock Vs of approximately 2600 m/s, 2650 m/s and 2850 m/s were obtained. The variability of these new measurements is smaller than previous studies and suggests higher confidence that the bedrock Vs is faster than 2500 m/s.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.488

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