Hydroacoustic tertiary (T-) waves are seismically generated acoustic waves that propagate
over great distances in the ocean sound channel with little loss in signal strength.
Hydrophone recorded T-waves can provide a lower earthquake detection threshold and an
improved epicenter location accuracy for oceanic earthquakes than land-based seismic
networks. Thus detection and location of NE Pacific ocean earthquakes along the Blanco
Transform Fault (BTFZ) and Gorda plate using the U.S. Navy's SOSUS (SOund
SUrveillance System) hydrophone arrays afford greater insight into the current state of
stress and crustal deformation mechanics than previously available. Acoustic earthquake
information combined with bathymetry, submersible observations, earthquake source-parameter
estimates, petrologic samples, and water-column chemistry renders a new
tectonic view of the southern Juan de Fuca plate boundaries.
Chapter 2 discusses development of seismo-acoustic analysis techniques using the
well-documented April 1992 Cape Mendocino earthquake sequence. Findings include a
hydrophone detection threshold estimate (M~2.4), and T-wave propagation path modeling
to approximate earthquake acoustic source energy. Empirical analyses indicate that
acoustic energy provides a reasonable magnitude and seismic moment estimate of oceanic
earthquakes not detected by seismic networks. Chapters 3 documents a probable volcanogenic T-wave event swarm along a pull-apart basin within the western BTFZ during January 1994. Response efforts yielded evidence of anomalous water-column ��He concentrations, pillow-lava volcanism, and the first discovery of active hydrothermal vents along an oceanic fracture zone. Chapter 4 discusses the detection of a NE-SW trending microearthquake band along the mid-Gorda plate which was active from initiation of SOSUS recording in August 1991 through July 1992, then abruptly ceased. It is proposed that eventual termination of the Gorda plate seismicity band is due to strain reduction associated with the Cape Mendocino earthquake sequence. Chapter 5 combines bathymetric, hydro-acoustic, seismic, submersible, and gravity data to investigate the active tectonics of the transform parallel Blanco Ridge (BR), along the eastern BTFZ. The BR formation mechanism preferred here is uplift through strike-slip motion (with a normal component) followed by formation and intrusion of mantle-derived serpentinized-peridotite into the shallow ocean crust. The conclusion considers a potential link between the deformation patterns observed along the BTFZ and Gorda plate regions. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34150 |
| Date | 02 June 1997 |
| Creators | Dziak, Robert P. |
| Contributors | Yeats, Robert S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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