Seismic properties (P, S velocities and Poisson's ratio) of
young (0.75 m.y.) and mature (110 m.y.) oceanic crust are obtained
by studying explosive refraction data collected in the Pacific Ocean
using ocean bottom and downhole seismometers. A comparison of the
results for the two regions indicates that the upper crustal velocities
increase with age due to the cementation of cracks and fractures,
the upper mantle velocities increase with age due to cooling,
and the crust (mainly the lower crust) thickens with age. The Poisson's
ratios obtained in this study are too small to be consistent
with the presence of any serpentinization of the lower crust or
upper mantle which therefore precludes upper mantle serpentinization
as the cause for the thickening of the crust with age. When comparing
seismic structures of young and mature oceanic crust with
ophiolite models, we find close similarities between the Samail
ophiolite and young oceanic crust, and between the Bay of Islands
ophiolite and old oceanic crust. The 110 m.y. old crust of the
northwest Pacific Basin is characterized by high velocity gradients
in the upper crust, low velocity gradients in the lower crust, a
smooth 1 km-thick crust-mantle transition zone and the presence of a
minimum 14% anisotropy in the upper mantle compressional wave
velocities. Velocities are highest in an east-west direction. The
0.75 m.y. old crust at the intersection of the East Pacific Rise and
the Orozco fracture zone is characterized by a steady increase in
velocity with depth. A delay time analysis shows a trend to large
Layer 3 delay times in the Orozco fracture zone indicating a thicker
Layer 2 and/or low Layer 2 velocities.
An investigation of different model parameterizations for the
tau-zeta travel time inversion using a synthetic data set indicates
that the best velocity gradient solutions, based on the least deviation
of the solution from the true model, are obtained from models
in which the velocities of the layer bounds take on the values of
the observed velocities of the refracted waves. A trade-off curve
obtained from varying the number of layers in the model shows that a
model with as many layers as observed data points represents a satisfactory
compromise between model resolution and solution variance. / Graduation date: 1984
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29403 |
| Date | 30 March 1984 |
| Creators | Bee, Michel |
| Contributors | Bibee, L. Dale |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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