Dissertation/Thesis Abstract

Three dimensional crustal shear-wave velocity of central Idaho/eastern Oregon and a verified method for modeling upper mantle anisotropy
by Bremner, Paul M., Ph.D., University of Florida, 2016, 136; 10298924
Abstract (Summary)

We present new regional tectonic models of central Idaho and eastern Oregon. Seismic data obtained from the IDaho/ORegon (IDOR) Passive seismic network, 85 broadband seismic stations, were used to tomographically image isotropic and anisotropic crustal velocity structure beneath central Idaho and eastern Oregon. We additionally validate a new method to tomographically image isotropic and anisotropic upper mantle velocity structure. A detailed crustal model is required for an accurate upper mantle tomographic image. Ambient noise tomography was used to produce 3-D isotropic and anisotropic crustal velocity models from Love and Rayleigh wave group and phase velocity measurements on the IDOR dataset. We derived 2-D maps of azimuthal anisotropy as a function of period. We determined radial anisotropy with depth from the 3-D Love and horizontal component Rayleigh wave isotropic velocity models. Results from the isotropic crustal velocity models show a strong velocity contrast across the Western Idaho Shear Zone that is only visible in the shallow crust. Within the Idaho batholith, the area beneath the border zone and early metaluminous suites is moderately faster than that of the Atlanta peraluminous suite. West of the Western Idaho Shear Zone, the Bourne and Greenhorn subterranes have distinctly different seismic velocities at shallow crustal depths. We propose that the Bourne subterrane has a thin package of accretionary prism, and is underlain by an extension of Wallowa related arc or oceanic crust. More than 10 km of very slow velocity accretionary complex overlies a faster basement of the Greenhorn subterrane that could represent the remnant forearc partially exposed on the surface, or further extension of a Wallowa related arc or oceanic crust. Lastly, we laid the groundwork for future imaging of isotropic and anisotropic upper mantle seismic velocity structure using the method introduced by Panning and Nolet (2008). We validated new 3-D finite-frequency kernels through implementation on a synthetic dataset of 128 earthquakes of magnitude 6-7 between 2006 and 2009. The kernels are based on the Born approximation, and formulated for a hexagonal symmetry with an arbitrary fast axis orientation. The kernel predictions were compared against multi-taper fundamental mode surface wave phase delay measurements.

Indexing (document details)
Advisor: Panning, Mark
School: University of Florida
School Location: United States -- Florida
Source: DAI-B 78/05(E), Dissertation Abstracts International
Subjects: Geology, Geophysics
Keywords: Crustal velocity, Idaho, Oregon, Upper mantle
Publication Number: 10298924
ISBN: 978-1-369-41947-4
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