550 research outputs found
Cenozoic geology of the continental slope and rise off western Nova Scotia
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October 1985The outer continental margin of Nova Scotia is divided by a diapir
province, 40-110 km wide and ~1000km long, that trends subparallel to the
shelf edge along the upper continental rise and slope. The growth pattern
for a small region of this margin (61°-64°W) during the Late Cretaceous and
Cenozoic was studied using seismic stratigraphy and well data. Structure
maps show that a steep continental slope existed landward of the diapir
province (~2200-3800 m water depth) from Early Cretaceous until Miocene
time when onlapping upper rise sediments reduced the gradient. Shelf edge
canyons were cut during the late Maestrichtian-early Paleocene,
Eocene-Oligocene, and Pleistocene. Extensions of Tertiary canyons onto the
slope are poorly defined, but small Paleocene fans of interbedded chalk and
mudstone on the upper rise indicate that slope canyons existed at that
time. Abyssal currents eroded the upper rise and smoothed relief on the
continental slope in the Oligocene and middle(?) Miocene. In the Miocene,
turbidites may have ponded on the upper rise landward of seafloor highs
uplifted by salt ridges or pillows. Pliocene-Pleistocene sediments drape
over pre-existing topography. At the beginning and end of the Pleistocene,
turbidity currents, caused by delivery of large sediment loads to the shelf
edge by glaciers, eroded the present canyon morphology.
The late Cenozoic section of the lower continental rise thins seaward
from ~2 km near the diapir province and rests on Horizon Au, a prominent
unconformity eroded during the Oligocene by abyssal currents. The
morphology of the lower rise is largely due to construction by down-slope
deposits shed in the Miocene-Pliocene from uplift of the diapir province.
Abyssal currents episodically eroded sediment, but current controlled
deposition formed only a thin (<300 m) deposit in the Pliocene(?). Uplift
in the diapir province accelerated during the Pleistocene and olistostromes
up to 300 m thick were shed onto the lower rise. In the latest Pleistocene,
sediments transported down-slope by near-bottom processes accumulated west
of a sharp boundary running near 62°30'W from 500 m seaward to the abyssal
plain. To the east, hemipelagic sediments accumulated above 4300 m, while
turbidity currents, originating in deep canyons to the east, and abyssal
currents reworked sediments below 4300 m. A glacial sediment source and
relict shelf morphology controlled sedimentation processes and, thus, the
location of depocenters on the slope and rise
Modeling seafloor geoacoustic interaction with a numerical scattering chamber
Author Posting. © Acoustical Society of America, 1994. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 96 (1994): 973-990, doi:10.1121/1.410271.A numerical scattering chamber (NSC) has been developed to compute backscatter functions for geologically realistic seafloor models. In the NSC, solutions are computed to the elastic (or anelastic) wave equation by the finite-difference method. This has the following advantages: (a) It includes all rigidity effects in the bottom including body and interface waves. (b) It can be applied to pulse beams at low grazing angles. (c) Both forward scatter and backscatter are included. (d) Multiple interactions between scatterers are included. (e) Arbitrary, range-dependent topography and volume heterogeneity can be treated simultaneously. (f) Problems are scaled to wavelengths and periods so that the results are applicable to a wide range of frequencies. (g) The method considers scattering from structures with length scales on the order of acoustic wavelengths. The process is discussed for two examples: a single facet on a flat, homogeneous seafloor and a canonically rough, homogeneous seafloor. Representing the backscattered field by a single, angle-dependent coefficient is an oversimplification. In a strong scattering environment, time spread of the field is a significant issue and an angle-dependent separation of the wave field may not be valid.This work was carried out under support from the Office of Naval Research Acoustic Reverberation Special Research
(Grant Number N00014-90-J-149
Finite difference modeling of geoacoustic interaction at anelastic seafloors
Author Posting. © Acoustical Society of America, 1994. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 95 (1994): 60-70, doi:10.1121/1.408298.A major problem in understanding seismic wave propagation in the seafloor is to distinguish between the loss of energy due to intrinsic attenuation and the loss of energy due to scattering from fine scale heterogeneities and bottom roughness. Energy lost to intrinsic attenuation (heat) disappears entirely from the system. Energy lost to scattering is conserved in the system and can appear in observations as incoherent noise (reverberation, time spread, angle spread) and/or mode converted waves. It has been shown by a number of investigators that the seafloor scattering problem can be addressed by finite difference solutions to the elastic wave equation in the time domain. However previous studies have not considered the role of intrinsic attenuation in the scattering process. In this paper, a formulation is presented which includes the effects of intrinsic attenuation in a two-dimensional finite difference formulation of the elastodynamic equations. The code is stable and yields valid attenuation results.This work was carried out under Office of Naval Research
Grant no. N00014-89-J-1012
Lateral continuity of basement seismic reflections in 15 Ma ultrafast-spreading crust at ODP Site 1256
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Marine Geophysical Research 32 (2011): 429-439, doi:10.1007/s11001-011-9122-4.The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1000km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region, formed at an ultra-fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~ 1150m in basement. Multi-channel seismic traces show weak laterally coherent sub-basement reflections at borehole depths. Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. These seismograms show significant sub-basement amplitude peaks. A zero-offset vertical seismic profile, shot on E312, was processed to investigate the authenticity of these reflections and their relationship to borehole geology. A dual scheme of the median filtering and F-K dip filtering was used. Tests with synthetic seismograms indicate the approach is effective at reasonable SNR levels. Downgoing energy is clearly identified but negligible upgoing energy is visible over random noise. These results indicate that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales less than the Fresnel Zone (~ 300m) due to igneous and tectonic processes
An industrial sewing machine variable speed controller
The apparel industry is attempting to move in a new direction in the coming decade. Since the invention of an electrically powered sewing machine, the operator has been seated. Today, companies are switching from a sit down operation to a stand up operation involving modular stations. The old treadle worked well with the sitting operator, but problems have been found when trying to use the same treadle with a standing operator. This report details a new design for a treadle to operate an industrial sewing machine that has a standing operator. Emphasis is placed on the ease of use by the operator, as well as the ergonomics involved. Procedures for testing the design are included along with possible uses for the treadle in other applications besides an industrial sewing machine
Site synthesis report of DSPP sites 417 and 418
This document summarizes information relevent to planning, execution, and interpretation of results from a study of the interaction of
sound in the 2-30Hz band with deep ocean seafloor using sea-surface sources, seafloor receivers, and borehole seismometers emplaced
by wireline re-entry at Deep Sea Drilling Project sites 417 and 418 in the western North Atlantic. We summarize published scientific
results from borehole sampling of water, sediment, and rock, from wire line logging, and from borehole seismic experiments. We present
new results from analysis of total power recorded by receivers clamped in basement during the borehole seismic experiment on DSDP
Leg 102. We document non-drilling investigations of the site and the nature and location of re-entry cones and transponders. We describe
the physical oceanography of the region and the speed of sound in water. We provide an extensive bibliography on published results from
scientific investigations at 417/418. This document was completed prior to 1989 surveys of sites 417 and 418.Funding was provided by the Johns Hopkins University, Applied Physics Laboratory
under contract Number 602809-0
Recommended from our members
Poly(acrylic acid) interpolymer complexation: use of a fluorescence time resolved anisotropy as a poly(acrylamide) probe
YesA low concentration poly(acrylamide) sensor has been developed
which uses the segmental mobility of another polymer probe with a
covalently attached fluorescent marker. Interpolymer complexation
with poly(acrylic acid) leads to reduced segmental mobility which can
be used to determine the concentration of polymer in solution. This
technique could be useful in detecting the runoff of polymer dispersants
and flocculants in fresh water supplies following water purification
processes.Funding for the research was kindly provided by the Engineering and Physical Sciences Research Council (EPSRC)
Recommended from our members
Highly-branched poly(N-isopropyl acrylamide)s with core-shell morphology below the lower critical solution temperature
YesHighly-branched poly(N-isopropyl acrylamide)s in water pass through coil-to-globule transitions. Using
calorimetry and the colour change of a solvatochromic dye within the polymer, we show that some
compositions have biphasic core–shell morphologies, with globular cores and open coil shells. The two-phase
structure is favoured by increased branching and arises because the chain ends penetrate only to
a limited degree into the polymer coil
Bathymetry and sediment thickness survey of the Hawaii-2 cable : cruise report for Kiwi expedition leg 2 on the R/V Roger Revelle
The primary purpose of this cruise was to identify at least two potential
observatory sites along the Hawaii-2 cable that would be suitable for drilling a
hole to basement. There is a funded program, the Hawaii-2 Observatory (H20), to
install a junction box on the cable about mid-way between California and Hawaii
(Figures 1 and 2). We want to identify sites in advance so that drilling will be
possible near the observatory. This will permit a large range of borehole
experiments to be cared out continuously and in real time. Based on available
data we chose a section of cable between 140° and 143°W. This cable lies on a
ribbon of 'normal' oceanic crust with well defined magnetic anomalies and
relatively smooth bathymetry. The goals were to acquire SEABEAM bathymetry
data and single channel seismic reflection data along this section of cable, to
identify at least two potential sites along the cable and to car out SCS surveys
within about 10km radius of the sites. Since the H20 cable has been given to the scientific community it
is a valuable resource for research. While transiting to and from the
site we felt that it would be wortwhile to acquire SEABEAM data along
as much of the cable track as possible. This 'spec' data, Seabeam and
magnetometer data between 130°W and 155°W may be useful to other
investigators in the future.This work was carried out under the JOI Prime Contract OCE-93020477,
JOI Budget Code 44505-J130l0
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