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  • 1
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    Focused Fluid Flow Along the Nootka Fault Zone and Continental Slope, Explorer-Juan de Fuca Plate Boundary (2021)
    Details
    Publication Date: 2021-10-11
    Description: Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from 〉20 years of investigations to demonstrate the nature of fluid-flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near-seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite-to-seafloor reflection polarity, and are associated with frequency reduction and velocity push-down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high-amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom-video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios 〈500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate-related bottom-simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.
    Keywords: 551 ; fluid flow ; Nootka transform fault ; gas hydrate ; intrusion ; heat flow
    Language: English
    Type: map
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  • 2
    Electronic Resource
    Electronic Resource
    The Hatton Bank continental margin—I. Shallow structure from two-ship expanding spread seismic profiles (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 96 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Summary. The Hatton Bank passive continental margin exhibits thick seaward dipping reflector sequences which consist of basalts extruded during rifting between Greenland and Rockall Plateau. Multichannel seismic reflection profiling across the margin reveals three reflector wedges with a maximum thickness near 7 km, extending from beneath the upper continental slope to the deep ocean basin. We present results of the velocity structure within the dipping reflector sequences at eight locations across the margin, interpreted by synthetic seismogram modelling a set of multichannel expanding spread profiles parallel to the margin. At the top of some reflector sequences, we observe a series of 100 m thick high- and low-velocity zones, which are interpreted as basalt flows alternating with sediments or weathered and rubble layers. At the profile locations, the base of the dipping reflectors correlates with P-wave velocities near 6.5 km s−1. However, elsewhere the reflectors appear to extend significantly deeper than the inferred 6.5 km s−1 velocity contour, indicating that the velocity structure may not be controlled solely by lithological boundaries but also by metamorphic effects. Shear-waves were observed on two lines, permitting the calculation of Poisson's ratio. The decrease in Poisson's ratio from 0.28 to near 0.25 in the upper 5 km of crust may also indicate the effect of metamorphism on seismic properties, or alternatively may be explained by crack closure under load.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb04451.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The Hatton Bank continental margin—II. Deep structure from two-ship expanding spread seismic profiles (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 96 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Summary. The continent-ocean transition adjacent to Hatton Bank was studied using a dense grid of single-ship and two-ship multichannel seismic profiles. The interpretation of the explosive expanding spread profiles (ESPs) which were shot as part of this survey are discussed here in detail. Extensive seaward dipping reflectors are developed in the upper crust across the entire margin. These seaward dipping reflectors continue northwards on the Faeroes and Vøring margins, where they have been shown to be caused by basaltic lavas, as well as on the conjugate margin of East Greenland. The dipping reflectors are an important feature of the rifting history of the margin and show that extensive volcanism was associated with the extension. The ESPs show clear seismic arrivals out to ranges of 100 km. Wide-angle Moho reflections can be seen on all the lines as well as good mid and lower crustal arrivals. The determination of seismic velocity structure was constrained by ray tracing and by amplitude modelling using reflectivity synthetic seismograms. The results from the ESPs show that there is a thick region of lower crustal material beneath the margin with an unusually high crustal velocity of 7.3–7.4 km s−1. This lower crustal material reaches a maximum thickness of 14 km beneath the central part of the margin and is terminated at depth by the Moho. The lower crustal lens of high-velocity material is interpreted as underplated or intruded igneous rocks associated with the large volumes of extrusive basaltic lavas, now seen as dipping reflectors on the margin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb04452.x
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  • 4
    Electronic Resource
    Electronic Resource
    Decreased stability of methane hydrates in marine sediments owing to phase-boundary roughness (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 420 (2002), S. 656-660 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Below water depths of about 300 metres, pressure and temperature conditions cause methane to form ice-like crystals of methane hydrate. Marine deposits of methane hydrate are estimated to be large, amassing about 10,000 gigatonnes of carbon, and are thought to be important to global change and ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01263
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  • 5
    Electronic Resource
    Electronic Resource
    Upper Crustal Velocity Structure of the Southwestern Canadian Cordillera from Explosion Recordings on the WCTN Earthquake Seismic Net (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 1315-1336 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Seismic refraction, crustal velocity, Canadian Cordillera, tomographic inversion, earthquake seismic net, shear-wave velocities.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The digital seismic network used to monitor earthquakes in southwestern British Columbia recorded explosions from Lithoprobe’s Southern Cordillera Refraction Experiment (SCoRE) in 1989 and 1990 and from the USGS Pacific Northwest Refraction Survey in 1991. Both P and S waves were recorded. The geographical distribution of the shots and receiver stations enabled a large three-dimensional area to be sampled. For ray paths considered to be in the top 10 km of the crust, we used a tomographic inversion procedure to estimate the 2-D distribution of upper crustal P- and S-wave velocities within blocks of a refracting velocity grid, located beneath a near surface velocity layer of uniform thickness. The P-wave velocity distribution mapped the subsurface location of several terranes in the southwest Cordillera. Volcanic rocks of Wrangellia terrane, which is the principal component of the Insular Belt, were characterized by upper crustal velocities 〉 6.3 km s −1, whereas plutonic rocks of the Coast Belt had velocities 〈 6.3 km s−1. East of southern Vancouver Island, the velocity distribution indicated that Wrangellia extends in the subsurface beneath the Coast Belt for about 130 km eastward of the surface location of the Insular/Coast Belt boundary. A portion of the southern boundary of Wrangellia was also delineated by the P-velocity map, which suggested that metamorphic rocks of the Northwest Cascades Thrust System may extend beneath sedimentary cover as far west as south-central Georgia Strait. Inverted S-wave velocities were typically 3.6–3.7 km s−1. Corresponding values of Poisson’s ratio were 0.27–0.28 over Vancouver Island and 0.20–0.24 in the Coast Belt. The higher values for Vancouver Island likely reflect the high mafic content of Wrangellia volcanics, compared to the high quartz content of the Coast Belt plutonics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001121
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  • 6
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    A background correction algorithm for Van Allen Probes MagEIS electron flux measurements (2015)
    Wiley
    Details
    Publication Date: 2015-06-07
    Description: We describe an automated computer algorithm designed to remove background contamination from the Van Allen Probes MagEIS electron flux measurements. We provide a detailed description of the algorithm with illustrative examples from on-orbit data. We find two primary sources of background contamination in the MagEIS electron data: inner zone protons and bremsstrahlung X-rays generated by energetic electrons interacting with the spacecraft material. Bremsstrahlung X-rays primarily produce contamination in the lower energy MagEIS electron channels (~30-500 keV) and in regions of geospace where multi-MeV electrons are present. Inner zone protons produce contamination in all MagEIS energy channels at roughly L  〈 2.5. The background corrected MagEIS electron data produce a more accurate measurement of the electron radiation belts, as most earlier measurements suffer from unquantifiable and uncorrectable contamination in this harsh region of the near-Earth space environment. These background-corrected data will also be useful for spacecraft engineering purposes, providing ground truth for the near-Earth electron environment and informing the next generation of spacecraft design models (e.g., AE9).
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Penetration of magnetosonic waves into the plasmasphere observed by the Van Allen Probes (2015)
    Wiley
    Details
    Publication Date: 2015-09-13
    Description: During the small storm on 14-15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate towards lower L -shells outside the plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then gradually cross the plasmapause into the deep plasmasphere, with almost unchanged path gains due to the falling proton ring distribution and higher ambient density. These results present the first report on how MS waves penetrate into the plasmasphere with the aid of the continuous proton ring distributions during weak geomagnetic activities.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Evolution and slow decay of an unusual narrow ring of relativistic electrons near L ~ 3.2 following the September 2012 magnetic storm (2013)
    Wiley
    Details
    Publication Date: 2013-06-07
    Description: [1]  A quantitative analysis is performed on the decay of an unusual ring of relativistic electrons between 3 and 3.5 R E , which was observed by the REPT instrument on the Van Allen Probes. The ring formed on September 3, 2012 during the main phase of a magnetic storm due to the partial depletion of the outer radiation belt for L 〉 3.5, and this remnant belt of relativistic electrons persisted at energies above 2 MeV, exhibiting only slow decay, until it was finally destroyed during another magnetic storm on October 1. This long-term stability of the relativistic electron ring was associated with the rapid outward migration and maintenance of the plasmapause to distances greater than L = 4. The remnant ring was thus immune from the dynamic process, which caused rapid rebuilding of the outer radiation belt at L 〉 4, and was only subject to slow decay due to pitch angle scattering by plasmaspheric hiss on timescales exceeding 10–20 days for electron energies above 3 MeV. At lower energies the decay is much more rapid, consistent with the absence of a long duration electron ring at energies below 2 MeV.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Energetic electron precipitation: multi‐event analysis of its spatial extent during EMIC wave activity (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of 10s keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC‐driven precipitation, which occurred near the dusk sector observed by multiple Low‐Earth‐Orbiting (LEO) POES/MetOp satellites. During EMIC wave activity, the proton precipitation occurred from few 10s keV up to 100s keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi‐linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC‐driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L‐shell region (ΔL~0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and MLT sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Rapid flattening of butterfly pitch-angle distributions of radiation belt electrons by whistler-mode chorus (2016)
    Wiley
    Details
    Publication Date: 2016-08-17
    Description: Van Allen radiation belt electrons exhibit complex dynamics during geomagnetically active periods. Investigation of electron pitch-angle distributions (PADs) can provide important information on the dominant physical mechanisms controlling radiation belt behaviors. Here we report a storm-time radiation belt event where energetic electron PADs changed from butterfly distributions to normal or flattop distributions within several hours. Van Allen Probes observations showed that the flattening of butterfly PADs were closely related to the occurrence of whistler-mode chorus waves. Two-dimensional quasi-linear STEERB simulations demonstrate that the observed chorus can resonantly accelerate the near-equatorially trapped electrons and rapidly flatten the corresponding electron butterfly PADs. These results provide a new insight on how chorus waves affect the dynamic evolution of radiation belt electrons.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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