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  • 1
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    Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge (2000)
    In:  Nature, San Francisco, Schweizerbart'sche Verlagsbuchhandlung, vol. 407, no. 6801, pp. 174, pp. L14306, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Details
    Publication Date: 2000
    Keywords: Fluids ; Plate tectonics ; Earthquake ; Stress ; Nabelek
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Contemporary Ocean Warming Dissociates Cascadia Margin Gas Hydrates (2014)
    Wiley
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    Publication Date: 2014-11-05
    Description: Gas hydrates, pervasive in continental margin sediments, are expected to release methane in response to ocean warming, but the geographic range of dissociation and subsequent flux of methane to the ocean are not well constrained. Sediment column thermal models based on observed water column warming trends offshore Washington (USA) show that a substantial volume of gas hydrate along the entire Cascadia upper continental slope is vulnerable to modern climate change. Dissociation along the Washington sector of the Cascadia margin alone has the potential to release 45–80 Tg of methane by 2100. These results highlight the importance of lower latitude warming to global gas hydrate dynamics and suggest that contemporary warming and downslope retreat of the gas hydrate reservoir occurs along a larger fraction of continental margins worldwide than previously recognized.
    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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  • 3
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    Analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope (2015)
    Wiley
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    Publication Date: 2015-10-02
    Description: Cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity. A portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the Vancouver Island and Oregon portions of the Cascadia margin. Multi-channel seismic reflection profiles on the Cascadia margin show the widespread presence of Bottom Simulating Reflectors (BSRs) within the sediment column, indicating the gas hydrate reservoir extends from the deformation front at 3000 meters depth to the upper limit of gas hydrate stability near 500 meters water depth. In this study, we compile an inventory of methane bubble plume sites on the Cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen. High plume density anomalies are associated with both the continental shelf (〈180 meters) and the depth of the upper limit of Methane Hydrate Stability Depth (MHSD) that occurs near 500 meters in the NE Pacific. The observed anomalies on the Cascadia slope may be due to the warming of seawater at intermediate depths, suggesting that modern climate change has begun to destabilize the climate-sensitive hydrate reservoir within the Cascadia margin sediments. Re-analysis of similar plume images on the North American Atlantic slope suggest a lack of correlation between observed plume depths and the MHSD for much of the latitudinal range. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    The thermal environment of Cascadia Basin (2012)
    Wiley
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    Publication Date: 2012-07-10
    Description: Located adjacent to the NE Pacific convergent boundary, Cascadia Basin has a global impact well beyond its small geographic size. Composed of young oceanic crust formed at the Juan de Fuca Ridge, igneous rocks underlying the basin are partially insulated from cooling of their initial heat of formation by a thick layer of pelagic and turbidite sediments derived from the adjacent North American margin. The igneous seafloor is eventually consumed at the Cascadia subduction zone, where interactions between the approaching oceanic crust and the North American continental margin are partially controlled by the thermal environment. Within Cascadia Basin, basement topographic relief varies dramatically, and sediments have a wide range of thickness and physical properties. This variation produces regional differences in heat flow and basement temperatures for seafloor even of similar age. Previous studies proposed a north-south thermal gradient within Cascadia Basin, with high geothermal flux and crustal temperatures measured in the heavily sedimented northern portion near Vancouver Island and lower than average heat flux and basement temperatures predicted for the central and southern portions of the basin. If confirmed, this prediction has implications for processes associated with the Cascadia subduction zone, including the location of the “locked zone” of the megathrust fault. Although existing archival geophysical data in the central and southern basin are sparse, nonuniformly distributed, and derived from a wide range of historical sources, a substantial N-S geothermal gradient appears to be confirmed by our present compilation of combined water column and heat flow measurements.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Quantitative estimate of heat flow from a mid-ocean ridge axial valley, Raven field, Juan de Fuca Ridge: Observations and Inferences (2014)
    Wiley
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    Publication Date: 2014-08-26
    Description: A systematic heat flow survey using thermal blankets within the Endeavour segment of the Juan de Fuca Ridge axial valley provides quantitative estimates of the magnitude and distribution of conductive heat flow at a mid-ocean ridge, with the goal of testing current models of hydrothermal circulation present within newly formed oceanic crust. Thermal blankets were deployed covering an area of 700 by 450 meters in the Raven Hydrothermal vent field area located 400 meters north of the Main Endeavour hydrothermal field. A total of 176 successful blanket deployment sites measured heat flow values that ranged from 0 to 31 W m -2 . Approximately 53% of the sites recorded values lower than 100 mW m -2 , suggesting large areas of seawater recharge and advective extraction of lithospheric heat. High heat flow values were concentrated around relatively small ‘hotspots’. Integration of heat flow values over the Raven survey area gives an estimate of conductive heat output of 0.3 Megawatts, an average of 0.95 Watts m -2 , over the survey area. Fluid circulation cell dimensions and scaling equations allow calculation of a Rayleigh number of approximately 700 in Layer 2A. The close proximity of high and low heat flow areas, coupled with previous estimates of surficial seafloor permeability, argue for the presence of small scale hydrothermal fluid circulation cells within the high porosity uppermost crustal layer of the axial seafloor.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge. (2014)
    Wiley
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    Publication Date: 2014-09-02
    Description: High-resolution, near-bottom vector magnetic data were collected by ROV Jason over the Raven hydrothermal vent field (47° 57.3’N 129° 5.75’W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the northwest on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 x 10 6  m 3 in volume.
    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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    Anomalous concentration of methane emissions at the continental shelf edge of the Northern Cascadia Margin (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract A recent compilation of methane plumes detected offshore Washington State includes 1772 individual bubble streams issuing from 491 discrete vent sites. The majority of these plume sites form a narrow 10 km‐wide band located shallower than 250 m water depth, with most sites located near the 175‐meter‐deep continental shelf break that tracks the head scarps of large submarine canyons. Archive multi‐channel seismic profiles over the Cascadia shelf and uppermost margin that were co‐located within a few hundred meters with active emission sites show methane bubble streams arise from listric/normal faults and triangular‐shaped regions of disturbed seismic reflectors that intersect the seafloor and extend several kilometers into the sub‐surface. Geological processes were evaluated for producing the narrow emission site depths including non‐uniform distribution of methane within the Cascadia accretionary sediment wedge and horizontal transfer of groundwater from on‐shore sub‐aerial sources. A model of enhanced sediment permeability arising from a contrasting response between the inner and outer portions of the accretionary wedge deformation during a megathrust earthquake cycle appears the most likely mechanism. This faulting is generated during extension of the overriding plate during megathrust earthquake cycles, with semi‐continuous permeability enhancement of the fluid pathways from excitation by contemporary incident seismic waves.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Sediment Gravity Flows Triggered by Remotely-generated Earthquake Waves (2017)
    Wiley
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    Publication Date: 2017-05-23
    Description: Recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the Cascadia Subduction Zone of the Pacific Northwest. We analyzed seafloor temperature, pressure, and seismic signals, and of video stills of sediment-enveloped instruments recorded during the 2011- 2015 Cascadia Initiative experiment, and seafloor morphology. Our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the April 11, 2012 M w 8.6 Indian Ocean earthquake, located more than 13,500 km away. These waves triggered a sequence of small slope failures on the Cascadia margin that led to sediment gravity flows culminating in turbidity currents. Previous studies have related the triggering of sediment-laden gravity flows and turbidite deposition to local earthquakes, but this is the first study in which the originating seismic event is extremely distant (〉10,000 km). The possibility of remotely triggered slope failures that generate sediment-laden gravity flows should be considered in inferences of recurrence intervals of past great Cascadia earthquakes from turbidite sequences. Future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Surficial permeability of the axial valley seafloor; endeavour segment, Juan de Fuca Ridge (2013)
    Wiley
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    Publication Date: 2013-06-30
    Description: Hydrothermal systems at mid-ocean spreading centers play a fundamental role in Earth's geothermal budget. One under-examined facet of marine hydrothermal systems is the role that permeability of the uppermost seafloor veneer plays in the distribution of hydrothermal fluid. As both the initial and final vertical gateway for sub-surface fluid circulation, uppermost seafloor permeability may influence the local spatial distribution of hydrothermal flow. A method of deriving a photomosaic from seafloor video was developed and utilized to estimate relative surface permeability in an active hydrothermal area on the Endeavour Segment of the Juan de Fuca Ridge. The mosaic resolves seafloor geology of the axial valley seafloor at sub-meter resolution over an area greater than 1 km 2 . Results indicate that the valley walls and basal talus slope are topographically rugged and unsedimented, providing minimal resistance to fluid transmission. Elsewhere, the axial valley floor is capped by an unbroken blanket of low permeability sediment, resisting fluid exchange with the subsurface reservoir. Active fluid emission sites were restricted to the high-permeability zone at the base of the western wall. A series of inactive fossil hydrothermal structures form a linear trend along the western bounding wall, oriented orthogonal to the spreading axis. High temperature vent locations appear to have migrated over 100 meters along-ridge-strike over the decade between surveys. While initially an expression of subsurface faulting, this spatial pattern suggests that increases in seafloor permeability from sedimentation may be at least a secondary contributing factor in regulating fluid flow across the seafloor interface.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Heat Flow and Fluid Flux in Cascadia's Seismogenic Zone (2013)
    Wiley
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    Publication Date: 2013-11-27
    Description: The Cascadia Subduction Zone in the northeast Pacific has generated a large number of megathrust earthquakes and poses the greatest recognized seismic hazard to the northwestern United States. To learn more about the risks this subduction zone poses, scientists from Washington and Oregon conducted a research cruise in August aboard the R/V Atlantis to collect data that would estimate the thermal structure of the “fully locked zone” of the Cascadia megathrust fault. This locked zone resists the continuous motion of two tectonic plates as they collide, storing compressional energy that produces large megathrust earthquakes when released by the abrupt failure of the locking process.
    Print ISSN: 0096-3941
    Electronic ISSN: 2324-9250
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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