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Seismic wave propagation in the MELT...

Hung, Shu-Huei.

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Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise./
Author:	Hung, Shu-Huei.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 1998,
Description:	227 p.
Notes:	Source: Dissertations Abstracts International, Volume: 60-01, Section: B.
Contained By:	Dissertations Abstracts International60-01B.
Subject:	Geophysics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9830458
ISBN:	9780591833010

Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise.
Hung, Shu-Huei.

Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise. - Ann Arbor : ProQuest Dissertations & Theses, 1998 - 227 p.

Source: Dissertations Abstracts International, Volume: 60-01, Section: B.

Thesis (Ph.D.)--Brown University, 1998.

This item must not be sold to any third party vendors.

This thesis conducts comprehensive investigations of on-going tectonic processes from observations and modeling of seismic waves propagating through the MELT Experiment area across the southern East Pacific Rise (EPR). In Chapter One, a moment-tensor inversion procedure is developed to derive the source mechanism of a sequence of teleseismic earthquakes about 300 km west of the 18$\\sp\\circ$S EPR. All the determined events are nearly pure normal faults striking in a variety of directions with significant non-double-couple components, which are likely due to simultaneously slip on randomly-oriented fault planes. The summed moment tensor indicates no preferred orientation of horizontal extension with maximum vertical compression, consistent with the release of thermal stresses in the cooling oceanic seafloor. In Chapter Two, a parallel multi-domain pseudospectral method is developed for simulation of seismic wave propagation in generalized inhomogeneous and anisotropic media. We illustrate the variabilities in wavefront geometry and waveform complexity for different anisotropic symmetries present in the Earth. In Chapter Three, we measure shear wave splitting parameters to constrain lithospheric anisotropy in the vicinity of the earthquake swarm. Most of the resolving fast polarization directions are subparallel to the plate motion vector, attributable to crystal fabrics formed by shearing mantle flow. Some of them are scattered nearly orthogonal to the spreading direction, associated with crack-induced crustal anisotropy. Waveform modeling is employed to test the hypothesis of double-layered anisotropy. The models reconstruct the observed splitting pattern and demonstrate that shear waves split in nonuniform anisotropic layers display frequency-dependent behavior. In Chapter Four, we combine observed and synthetic waveforms and travel-time delays recorded in the MELT seismometer array to characterize the nature of mantle upwelling beneath the EPR. The similar waveforms and broad delay patterns reveal no evidence for the existence of a narrow, low-velocity, melt-rich subaxial channel. We model incoming finite-bandwidth seismic waves propagating through narrow low-velocity zones that might be hidden beneath the ridge. A focused upwelling zone as narrow as 4 km with a 1 km/s S-wave velocity reduction can be easily detected by spike-shaped slow arrivals near the ridge axis, though the rich waveform variability is lost in the resolvable periods.

ISBN: 9780591833010Subjects--Topical Terms:

535228
Geophysics.

Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise.
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245 1 0 $a Seismic wave propagation in the MELT Experiment area: Probing the nature of intraplate earthquakes, lithospheric anisotropy and mantle upwelling in the vicinity of the southern East Pacific Rise.
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500 $a Source: Dissertations Abstracts International, Volume: 60-01, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Forsyth, Donald W.
502 $a Thesis (Ph.D.)--Brown University, 1998.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a This thesis conducts comprehensive investigations of on-going tectonic processes from observations and modeling of seismic waves propagating through the MELT Experiment area across the southern East Pacific Rise (EPR). In Chapter One, a moment-tensor inversion procedure is developed to derive the source mechanism of a sequence of teleseismic earthquakes about 300 km west of the 18$\\sp\\circ$S EPR. All the determined events are nearly pure normal faults striking in a variety of directions with significant non-double-couple components, which are likely due to simultaneously slip on randomly-oriented fault planes. The summed moment tensor indicates no preferred orientation of horizontal extension with maximum vertical compression, consistent with the release of thermal stresses in the cooling oceanic seafloor. In Chapter Two, a parallel multi-domain pseudospectral method is developed for simulation of seismic wave propagation in generalized inhomogeneous and anisotropic media. We illustrate the variabilities in wavefront geometry and waveform complexity for different anisotropic symmetries present in the Earth. In Chapter Three, we measure shear wave splitting parameters to constrain lithospheric anisotropy in the vicinity of the earthquake swarm. Most of the resolving fast polarization directions are subparallel to the plate motion vector, attributable to crystal fabrics formed by shearing mantle flow. Some of them are scattered nearly orthogonal to the spreading direction, associated with crack-induced crustal anisotropy. Waveform modeling is employed to test the hypothesis of double-layered anisotropy. The models reconstruct the observed splitting pattern and demonstrate that shear waves split in nonuniform anisotropic layers display frequency-dependent behavior. In Chapter Four, we combine observed and synthetic waveforms and travel-time delays recorded in the MELT seismometer array to characterize the nature of mantle upwelling beneath the EPR. The similar waveforms and broad delay patterns reveal no evidence for the existence of a narrow, low-velocity, melt-rich subaxial channel. We model incoming finite-bandwidth seismic waves propagating through narrow low-velocity zones that might be hidden beneath the ridge. A focused upwelling zone as narrow as 4 km with a 1 km/s S-wave velocity reduction can be easily detected by spike-shaped slow arrivals near the ridge axis, though the rich waveform variability is lost in the resolvable periods.
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