Electronic Theses and Dissertations

Identifier

5992

Date

2017

Date of Award

7-13-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Earth Sciences

Concentration

Geophysics

Committee Chair

Chris Cramer

Committee Member

Christine Powell

Committee Member

Mitchell Withers

Committee Member

Shahram Pezeshk

Abstract

The Mississippi Embayment (ME) area is prone to damaging earthquakes as it lies over the New Madrid Seismic Zone, which is considered the most seismically active zone in the central and eastern United States. Several attempts have been made to account for the influence of deep sediment deposits of the ME on the propagation of seismic waves. This study presents the seismic and liquefaction hazards of the ME by adding the local geologic conditions to the 2014 USGS National Seismic Hazard Model. Both equivalent linear and nonlinear site response codes have been used to determine the amplification distribution at a site. This study uses the most up-to-date information available from different researchers and attempts to reduce the effect of uncertainties. A new 3D geologic model has been generated to assign geologic information and shear wave velocity to the soil profiles distributed over the ME area. The 3D model helps to generate an interpolated soil profile at a site for more accurate site response analysis, replacing the use of generic soil profiles. For liquefaction hazard analysis, updated surface geologic maps and liquefaction potential curves have been used. At short periods corresponding to peak ground acceleration the results show that seismic hazard is reduced on the lowlands in comparison to USGS results, mainly due to deamplification of ground motions from strong nonlinearity in the softer soil deposits. The NOAH (nonlinear Iwan model) site response code shows slightly lower hazard on the lowland soils in comparison to those obtained from SHAKE91 (equivalent linear). At long periods, lowlands deposits amplify hazards more in comparison to corresponding USGS results, mainly due to much less soil nonlinearity at long periods. The liquefaction hazard tends to be high in Holocene and late Pleistocene lowlands sediments and low in Pleistocene loess of the uplands. The young sediments and shallow groundwater table depth in lowlands contribute to higher liquefaction hazard. Considering pore pressure effects in nonlinear site response analysis at a test site on the lowlands shows amplification of ground motion even at short periods. Therefore, pore pressure effects should be considered in seismic hazard analysis of the ME.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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