Electronic Theses and Dissertations

Identifier

1281

Date

2014

Date of Award

12-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Earth Sciences

Concentration

Geophysics

Committee Chair

Charles Adam Langston

Committee Member

Christine Powell

Committee Member

Bob Smalley

Committee Member

Eunseo Choi

Abstract

Part 1: Two large explosions were recorded by a dense array of strong-motion accelerometers and rotational seismometers in northeastern Taiwan. The objective of this experiment was to test the response of the experimental Eentec rotational seismometers against calculated array rotations. Computed array rotation rates are seen to have little variation across the array, but point rotation rate measurements show significant deviations with each other and with the array rotation rates in the range of 3-5 Hz. It is not likely that the differences seen in the point and array-computed rotation rates are due to nonlinear or heterogeneous site conditions under each array element since these effects should also be seen in the acceleration data used to determine rotation rate.Part 2: Three experiments were performed to investigate whether off-the-shelf geophones and seismographs can be used to perform meaningful gradiometry measurements. A standard linear refraction experiment was performed to investigate the slowness of P and Rayleigh waves from hammer sources to compare with measurements taken from two gradiometer designs. One design consists of four, six-instrument gradiometers in a linear array to test the location abilities of the entire gradiometer array. A second gradiometer experiment involved superimposed cells to explore precision in calculation of spatial gradients. We conclude that off-the-shelf equipment can be used to construct small, dense gradiometer arrays.Part 3: Data from a dense array in Belmont County, Ohio were analyzed with seismic-wave gradiometry techniques in an effort to directly image structure associated with mined areas under the array. In particular, work concentrated on examining how two of the wave parameters, phase slowness and propagation azimuth, varied with position in the array. The parameters are found to be locally inconsistent when comparing shots of varying azimuths, but they are similar for shots at the same distance and azimuth, indicating a great deal of wave scattering within and outside of the dense array deployment. It is difficult to ascribe phase velocity or wave propagation azimuth directly to structure under small gradiometers.

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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