Dissertation Defense Announcement

Herff College of Engineering announces the Final Dissertation Defense of

Arash Yarahmadi

for the Degree of Doctor of Philosophy

July 1, 2019 at 1:00 PM in Engineering Building

Advisor: Shahram Pezeshk

Site Effects Study in the Mississippi Embayment and Uncertainties Evaluation in Site Response Analysis

ABSTRACT: There are several methods for obtaining seismic site effects; the standard spectral ratio (SSR) method is one of them. The critical assumption in this method is that the record of a surface reference rock site is equivalent to the input motion at the base of the soil layer. Performing SSR depends on the availability of a proper reference site for which the site amplification is negligible. In this study, we investigate a series of stations near the New Madrid seismic zone (NMSZ) to find stations adjacent to the Mississippi embayment (ME) that have the characteristics of a reference station. Furthermore, we use the most suitable reference station to find site amplification inside the ME. For finding reference stations, we categorize the considered stations by their fundamental frequencies and their average shear-wave velocities. We use the horizontal to vertical spectral ratio (HVSR) method to find the amplification factors of 10 stations located mostly in the west side of the ME. We used an inversion method to find site amplification factors of 6 station inside the ME. Uncertainties exist inherently in seismic site amplification functions and site-specific response analysis results are partly originated from variabilities in soil and local site conditions. these uncertainties can affect the results of surface seismic hazard or surface ground motions obtained by site response analysis (SRA). In SRA these uncertainties are accounted for by generating random cases of soil parameters. Choosing a suitable randomization bound can decrease the effects of uncertainties of soil parameters in SRA results like predicted spectral accelerations. Vertical seismometer arrays provide a great opportunity to study the variability exist in SRA by comparing predicted and observed surface ground motions. In this study we provide coefficient of variations for different parameters of the soil and we show that they vary by different periods. We perform 1-D equivalent linear SRA with SHAKE program for ground motions with peak ground acceleration (PGAs) more than 0.05g in four vertical seismic stations with different site classes in japan belong to KIK-Net seismic network using soil log profiles and ground motions data available in Kik-Neat database.