Electronic Theses and Dissertations

Identifier

1263

Date

2014

Date of Award

11-21-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Earth Sciences

Concentration

Geophysics

Committee Chair

Chris H. Cramer

Committee Member

Stephen Horton

Committee Member

Oliver Boyd

Committee Member

Shahram Pezeshk

Abstract

Part 1: Three-dimensional wave gradiometry is applied to data collected in an array field experiment composed of experimental three-component micro-electro-mechanical-system (MEMS)-based accelerometers. The objective of the experiment is to obtain near-surface shear wave velocity and shear strain in order to study nonlinear soil behavior. A weak motion and synthetic dataset were used to test the methods to calculate spatial derivatives and their uncertainties, and wave gradiometry coefficients. Displacement gradient in all three Cartesian directions are also calculated. The gradients are used to form displacement gradient tensor, giving strains and rigid body rotation. The synthetic dataset is used to help in understanding the results from the field observations. Part 2: Nonlinear soil behavior can be illustrated by a shear modulus reduction curve where shear modulus decreases as shear strain increases. A field experiment is performed to develop the reduction curve from in-situ measurements. An array of experimental three-component MEMS-based accelerometers is deployed to record strong ground motion produced by a large shaker truck with frequencies ranging from 5-40 Hz and different driving force amplitude. Wave gradiometry and the calculated displacement gradient are used to measure the change in phase velocity and shear strain, respectively, as a function of frequency and driving force amplitude. Shear strains produced by the propagating strong ground motions can be up to 1.4 x 10-4. Part 3: The question of whether a single ground motion intensity correlation equation (GMICE) is applicable to both eastern North America (ENA) and California is examined. The issue is addressed by collecting the datasets from previous studies. Additional data from recent earthquakes in ENA are added. The median of ground motion values at each modified Mercalli intensity (MMI) level and their uncertainties are calculated for peak ground velocity (PGV), peak ground acceleration (PGA), and spectral acceleration (Sa) at 0.3, 1.0, and 2.0 s. I find that the median value of PGV, Sa at 1.0 and 2.0 s at any particular intensity is higher for California than the ENA. A log-linear-fit of MMIto the median values of ground motion is used to determine a GMICE specific to each region.

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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