Dissertation/Thesis Abstract

Analysis of off-axis, low-velocity zones on the flanks of the Endeavour segment of the Juan de Fuca Ridge
by Wells, Anne Elizabeth, M.S., University of Oregon, 2012, 140; 1508954
Abstract (Summary)

Seismic data from the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge reveal several crustal-level, low-velocity, high-attenuation regions on the eastern and western ridge flanks 7 to 16 km from the neovolcanic zone. I examine Pg amplitude anomalies for a wide variety of source-receiver azimuths in the Endeavour active source seismic tomography data. I use finite difference waveform forward modeling to estimate the dimensions, depth, and seismic properties of the best-observed inferred anomalous regions. The attenuating regions extend 10–15 km beneath axis-parallel bathymetric highs and from 2 to 4 km below the seafloor. The velocity reduction is small (∼8%) and the attenuation large ( QP ≈ 8–40) suggesting the presence of partial melt. I infer that melt focusing toward the neovolcanic zone is incomplete and that tectonic interactions with the Heckle seamount chain and/or the large segment-bounding overlapping spreading centers may promote off-axis melt delivery at the Endeavour segment.

Indexing (document details)
Advisor: Hooft, Emilie
Commitee: Humphreys, Eugene, Toomey, Douglas, Wilcock, William
School: University of Oregon
Department: Department of Geological Sciences
School Location: United States -- Oregon
Source: MAI 50/05M, Masters Abstracts International
Source Type: DISSERTATION
Subjects: Geology, Geophysics
Keywords: Geology, Geophysics, Magma, Marine, Seismology
Publication Number: 1508954
ISBN: 9781267290328
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