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Microseismicity on the Gorda RidgeSolano-Borrego, Ariel E. 23 February 1982 (has links)
The seismicity at the northern section of the Gorda Ridge has been
studied with Ocean Bottom Seismographs. Nearly one hundred earthquakes
were located with RMS travel time residuals less than 0.5 seconds.
Most of these events lie within or near the array and they are probably
associated with the dynamics of crustal formation which creates the
observed bench-like features in the Gorda Ridge. An average of 5 microtremors
per hour can be detected in the median valley with a lower
activity outside of the ridge. Considerable clustering in time can
be seen and it is typical of a main-shock sequence with the largest
shock at or very near the beginning followed by a progressive decay
in number. Clustering was spatial as well as temporal and the records
indicate that they have similar mechanisms. A brittle zone of 18 km
thickness at 42°N and 13 km at 42.5°N was found implying any possible
magma chamber must be at greater depth. These thicknesses are larger
than those observed in the Mid Atlantic ridge and in the East Pacific
Rise. They may be explained by the depression of isotherms due to the
heat lost by the contact of the ridge with the old and cold plates
across the Blanco and the Mendocino Fracture Zones.
Comparison of earthquakes locations using only OBS with those obtained
from land stations indicate a major P-delay for the Gorda Basin.
The seismic activity appears to decrease markedly to the south of
42°N. This drop in activity indicates that the southern part of the
ridge is more stable than the northern part. This decrease in activity
is not consistent with a southward propagating rift if we accept that
higher seismicity levels are expected at the tip of the propagating
ridge segments. / Graduation date: 1982
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Paleomagnetic inclination shallowing in deep-sea sedimentsArason, Pórdur 18 April 1991 (has links)
In this thesis anomalous downcore shallowing of paleomagnetic
inclinations is interpreted to be caused by sediment compaction. Thus,
compaction-induced inclination shallowing may influence tectonic
reconstructions that are based on inclinations from deep-sea sediment
cores.
Progressive downcore shallowing of the remanent inclination was
observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea
Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top
of the section the average inclination corresponds to the expected
geocentric axial dipole value of 53° but shallows downcore by about 6°
to 8°. In sediments spanning the same time interval of neighboring site
576, no inclination shallowing was observed. This second site has
considerably lower sedimentation rates, and the Plio- Pleistocene is
represented by a 26-m sedimentary section. The inclination shallowing
at site 578 was correlated to a downhole decrease in porosity, and these
results are interpreted to suggest that both the downhole inclination
shallowing and decrease of porosity in site 578 were caused by sediment
compaction.
Microscopic models demonstrate that sediment compaction may lead
to inclination shallowing of the magnetic remanence. Furthermore, it is
shown that inherent initial within-sample dispersion of the magnetic
moments will transform any form of microscopic mechanism to an
equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I,
where I is the inclination of the ambient field, ΔI is the inclination
shallowing, a is a constant and ΔV the compaction.
Paleomagnetic inclinations of Cretaceous DSDP sediments from the
Pacific plate are known to be systematically shallower than predicted
from paleolatitudes of hot spot reconstructions. Published paleomagnetic
data were reexamined and the shallow Cretaceous inclinations explained
as a result of sediment compaction. The Cretaceous data are used to
estimate the parameter a. The resulting a values are comparable to those
of previous studies of compaction-induced inclination shallowing, both
from laboratory experiments and the considerably younger deep-sea
sediments at site 578. Values of the parameter a suggest that it might be
controlled by sediment lithology with greater shallowing for clayey than
calcareous sediments. / Graduation date: 1991
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Precise measurements of coda buildup and decay rates of western Pacific P, P₀ and S₀ phases and their relevance to lithospheric scatteringBrandsdottir, Bryndis 03 October 1986 (has links)
Graduation date: 1987 / Best scan available for figures.
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Evaluation of data-poor and age-structure management strategies for west coast rockfishArnold, Linsey M. 24 February 2012 (has links)
Management strategies to prevent overfishing while achieving optimum yield vary according to the available data and life history of the fished stock. I evaluated two sets of management strategies for Pacific coast rockfish: strategies to set harvest limits for data-poor stocks, and strategies intended to protect the age structure of fished stocks. Setting Harvest Limits for Data-poor Stocks - The collapse of canary rockfish, Sebastes pinniger, in the northeast Pacific began more than two decades before the stock was officially declared overfished. The 2006 reauthorization of the Magnuson-Stevens Fishery Conservation and Management Act requires a scientifically-based harvest limit for all fished stocks, including those with data limited to catch. Two such "data-poor" methods are currently in use for the management of west coast stocks, depletion-corrected average catch (DCAC) and depletion-based stock reduction analysis (DB-SRA). To evaluate the performance of each method when challenged with catch and biological uncertainty, I retrospectively applied the methods to the catch and biological data available at the time of the first and second canary rockfish stock assessments in 1984 and 1990. In 1980 canary rockfish would be classified as "data-poor", and in 1990 as "data-rich". To evaluate the sensitivity of DCAC and DB-SRA to error in the catch data, harvest limits were estimated using both the historic catch data from each assessment, and the reconstructed catch data from the most recent stock assessment. In addition, harvest limits were estimated using simulated catch data sets for the years 1916 to 1983 with increasing variability around the true catch. DCAC and DB-SRA estimated harvest limits were significantly lower than the catch recommended in both the data-poor and data-rich stock assessments, but higher than the "true" overfishing limit. Use of current catch data improved the estimated harvest limit when the stock was data-poor, but not when the stock was data-rich. The simple methods responded to increasing error in the catch time series with decreasing mean estimates of the harvest limit, indicating that these methods are highly precautionary for this species, when the catch time series is the only source of error. Age Structure Management Strategies - In a variable oceanographic environment, a population with many reproductive age classes benefits not only from the increased fecundity of older fish; but also, in some species, an increase in larval fitness. Older females may also spawn at different times or over longer periods than younger females, increasing the probability of larvae encountering favorable environmental conditions. Despite the accumulating evidence for the importance of age structure to long-term population viability in harvested fish populations, long-lived west coast rockfish (Genus Sebastes) are managed with a biomass-based harvest control rule. I compared three strategies for age structure management, and evaluated the strategies relative to the status quo, biomass-based harvest control rules, across three rockfish life histories. I examined the tradeoff between yield and traditional management reference points, as well as performance measures that could serve as management reference points for age structure. Yield was reduced by strategies that maintain "old growth" age structure, but annual variation in the catch and the probability of becoming overfished were also reduced. The longest-lived rockfish benefited the most from strategies that maintained older fish in the population through dome-shaped selectivity. The shorter-lived rockfish benefited from adjustments in the catch limit based on the age composition of the catch one year previous. Achieving "pretty good yield" with management strategies that also decrease the potential for overexploitation is an important goal for stocks that are well-studied and those that are poorly understood; these investigations contribute to a growing literature on alternative approaches to sustainable fisheries management. / Graduation date: 2012
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The effects of harvesting Pacific hake (Merluccius productus) on the offshore community : the results of a multi-species modelGartz, Russell G. 05 December 1994 (has links)
The effects of harvesting Pacific hake (Merluccius productus)
were examined with a multi-species numerical model composed of
seven logistic growth equations coupled by a food web. The
food web was composed of: California sea lions (Zalophus
californianus), hake, sablefish (Anaplopoma fimbria), spiny
dogfish (Squalus acanthias), a generic rockfish species
(Sebastes spp.), Northern anchovy (Engraulis mordax), and a
generic euphausiid species (as an example, Pacific krill,
Euphausia pacifica). The model was tuned to mimic stock
assessment biomass estimates for the years 1980 to 1991, after
which a short term experiment and a sensitivity analysis were
conducted. The short term experiment used a factorial design,
with hake fishing and fishing for rockfish, sablefish, and
anchovy as treatments. It was analyzed with scale analysis
techniques. The results indicate that hake (from a management
viewpoint) is potentially most important in the offshore
community as a prey item for sea lions and as a predator on
anchovies, but hake fishing mortality had a small effect on
either population during the time span of the experiment.
Results also suggest that hake has little or no competitive
interaction with other species that are trophically similar.
Increased harvesting of hake would probably do little to
increase the biomass of rockfish or sablefish. The general
conclusion of both the sensitivity analysis and the experiment
is that species below their carrying capacity are mostly
affected by changes in growth and removal processes while
species close to their carrying capacity are mostly affected
by processes controlling prey availability.
A forty year projection from 1991 to 2031 was conducted
to examine the effects of hake fishing on sea lion and anchovy
biomass. Results indicate that sea lion biomass will vary
inversely with hake fishing effort, while anchovy biomass is
directly proportional to hake fishing effort. Results also
indicate that hake experience environmental conditions not
favorable to recruitment. During favorable conditions the hake
population builds up a "surplus" that carries it through
periods of unfavorable conditions. Increased hake fishing
effort reduces the response of the population to favorable
conditions. The results of this research constitute a step
from the theory toward the practice of proactive multi-species
and ecosystem management. / Graduation date: 1995
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Distribution and prediction of Swiss needle cast of Douglas-fir in coastal OregonRosso, Pablo H. 17 October 2001 (has links)
This study was directed to improve our understanding of the ecology of Swiss needle
cast (SNC) of Douglas-fir, a disease that produces extensive damage to forests and
plantation in the coastal region of Oregon and Washington. A disease prediction model
for the coastal area of Oregon was built by establishing the relationship between the
distribution of disease severity and the environment. Currently available methods of
determining the distribution of SNC were analyzed, and the possibility of mapping the
disease using Landsat TM satellite images was explored.
Two types of regression approaches were used to study the relationship between
disease severity and climate, topography, soil and forest stand characteristics. Although
both types provided useful information and insight, the multiple regression approach was
chosen over the regression tree analysis to build the model, due to its capacity to
produce a continuous prediction response.
Fog occurrence, precipitation, temperature, elevation and slope aspect, were the
variables that contributed to explain most of the disease severity variability. Findings
agree with and formalize our previous understanding of the ecology of SNC: cool and
wet conditions in summer appear to increase disease severity. When the model was
applied to past climate conditions, retrospective predictions suggest that changes in
climate in the last two decades could help to explain the observed recent regional
increase in SNC disease severity.
The resulting model was used to construct a disease prediction map. This map
showed an accuracy equivalent to the currently available SNC aerial survey. The
prediction model, however, is able to produce a continuous prediction surface, more
suitable for testing and appropriate for assisting in disease management and research.
A strong relationship between mature stand canopy defoliation and the Landsat TM
indices greenness and brightness, indicates that it is possible to use satellite imagery to
map SNC. In contrast, young stands showed high variability, most likely due to the
relatively high proportion of exposed understory vegetation.
The possibility of mapping stand defoliation is of great importance because this
symptom can be directly linked to tree growth and forest productivity. Satellite imagery
can be used in future and in retrospective disease mapping. / Graduation date: 2002
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An investigative study in the systematic application of effectiveness indicators for institutional improvement in northwest community collegesSorensen, James E. 15 April 1998 (has links)
In 1990, the Northwest Association of Schools and Colleges moved to an
accreditation model based on outcomes, their assessment and deliberative attempts at
institutional change and improvement. No study existed in northwest community colleges
which identified the systematic application of effectiveness indicators for institutional
change and improvement. This study was conducted with primary administrators in
northwest community colleges that have completed the regional accreditation process
since 1990. It examined the perceived importance of using effectiveness indicators for
assessing institutional outcomes, and their congruence with actual or potential use in
making institutional change and improvements.
This study shows there is a positive relationship in community colleges between
the development of institutional effectiveness indicators and institutional change and
improvement. All administrators believed they should be using effectiveness indicators but
used them in varying degrees for planning, improving services, budgeting, accreditation,
program review and other decision making processes essential to the functioning of
community colleges. Although the use varied by category and administrative subgroup,
those administrators who had used effectiveness indicators believed their use led to
positive institutional change.
In order for this study to have an affect on northwest community colleges, several
important conditions need to be addressed. The Northwest Association of Schools and
Colleges must enforce Policy Statement 2.2, Policy on Educational Assessment, which
requires the adoption of an institutional effectiveness model. Community colleges must
embrace this model as a mechanism useful for the continuous improvement process.
Faculty, staff, administrators and boards must be trained in the application and use of the
institutional effectiveness model. Boards must establish outcomes or institutional goals
based on their unique mission and must hold the community college president accountable
for the achievement of institutional outcomes and the implementation of an assessment
process. Assessment must be completed at all levels of the institution. Institutions must
adopt an assessment model that reflects the institutions goals and objectives, and place its
responsibility prominently within the organization. Finally, measures must be developed at
each level or process by the persons closest to the process.
Failure to enforce accreditation standards will lead to publicly enacted performance
indicators aimed at achieving institutional effectiveness or accountability. / Graduation date: 1998
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Plant growth, thermal stress response, and enzyme kinetic relationships in native wetland and introduced grassesBrewer, Tim G. 19 December 1996 (has links)
Graduation date: 1997
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Total exposure profiles of azinphosmethyl and azinphosmethyl-oxon to orchard workers in the Pacific NorthwestMoate, Thomas F. 09 May 1996 (has links)
Graduation date: 1996
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Taxonomy of some endophytic and epiphytic genera of Phaeophyta on the Oregon coastO'Flaherty, Mary Louise 11 May 1966 (has links)
Graduation date: 1966
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