Doctoral Dissertations

Keywords and Phrases

Complex anisotropy; Mantle Dynamics; Seismic Anisotropy; Shear wave splitting; Splitting parameters; Tien Shan Orogenic Belt

Abstract

"In spite of numerous studies, the mechanisms for the crustal shortening, mountain formation and associated tectonism leading to complex or simply seismic anisotropy formation beneath the Tien Shan Orogenic Belt is still debated. The most popular hypotheses suggested for the existence of seismic anisotropy are small-scale mantle convection, regional scale resistive basal shear and APM induced asthenospheric flow. Here, we used shear-wave splitting (SWS) measurements with good azimuthal coverage to provide additional constraints on the various models proposed by previous studies. One of the most effective approaches utilized to constrain convective mantle flow patterns is the splitting of P-to-S converted phases at the core-mantle boundary on the receiver side (XKS including PKS, SKKS, and SKS). Consequently, a robust procedure involving automatic and manual batch processing to reliably assess and objectively rank shear-wave splitting parameters were used. The resulting 2089 pairs of well-defined XKS splitting parameters obtained from 25 stations located in the study area were broad enough to make a reliable determination about the existence or absence of complex anisotropy. Out of the 25 stations, measurements from 10 stations show insignificant azimuthal variations, the majority of stations demonstrating strike parallel E-W fast orientation. A remarkable feature of the fast orientations observed at the 15 stations is a clear azimuthal variation with a 900 periodicity, indicating the existence of two-layer anisotropy. Thus, the strike-parallel upper layer anisotropy is caused by lithospheric shortening, and anisotropy in the lower layer is associated with WNW-ward flow of asthenospheric material sandwiched between the subducting Tarim lithosphere and the thick Kazakh lithospheric root"--Abstract, page iv.

Advisor(s)

Gao, Stephen S.

Committee Member(s)

Liu, Kelly H.
Rogers, David J.
Anderson, Neil L. (Neil Lennart), 1954-
Mickus, Kevin L.

Department(s)

Geosciences and Geological and Petroleum Engineering

Degree Name

Ph. D. in Geology and Geophysics

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2015

Pagination

xii, 112 pages

Note about bibliography

Includes bibliographic references (pages 107-111).

Geographic Coverage

Tien Shan

Rights

© 2015 Solomon Gerra Cherie, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Library of Congress Subject Headings

Shear waves -- Measurement
Anisotropy
Earth (Planet) -- Mantle
Orogenic belts -- Tien Shan

Thesis Number

T 10710

Electronic OCLC #

913389914

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Dissertation Location

 
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