Crustal and upper mantle structures in the West Philippine Basin,
along 17-18°N, have been determined using explosions as sources and
ocean bottom seismometers to measure refracted compressional waves.
Seismic refraction profiles out to nearly 500 km were completed.
Shallow structure was measured using small shots, 1-240 lbs., and
the deeper structure was probed with large explosions, 0.9-1.8 tons.
A velocity-depth inversion using short range data shows the
upper crust to have strong velocity gradients which gradually decrease
with depth. The lower crust is characterized by a nearly constant
velocity gradient of 0.24 sec⁻¹. Standard delay-time functions and
a modified function accounting for lateral velocity gradients were
also used in travel time inversion. Results from the two methods are
comparable and yield ~1.5 km transitional zone thicknesses in the
basin. Although they vary slightly in magnitude between methods,
West Philippine Basin oceanic layer thicknesses are abnormally thin,
by about 2 km, when compared to average crust. Total crustal thicknesses
are shown to be thinner in the eastern part of the basin, approaching
only 3 km. Crustal thinning toward the east is consistent
with the Palau-Kyushu Ridge being a remnant transform fault connecting
Philippine and Kula-Pacific ridges in the past.
Predicted water depths in the basin are about 300 meters shallower
than observed depths when compensated to average mantle depths
found for the Western North Pacific. The depth anomaly cannot
be fully reconciled by thin crust, and requires a deeper-seated
anomaly to be present in the West Philippine Basin.
Temperature and pressure modeling using experimental measurements
from proposed mantle constituents indicate high seismic
gradients in the upper mantle and may suggest that a multi-component
or graded mantle exists beneath the marginal sea. / Graduation date: 1983
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29157 |
| Date | 15 April 1983 |
| Creators | Goodman, Dean |
| Contributors | Bibee, L. Dale |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0024 seconds